Overheating question

[Nate88]

So I got my first slice of the downs in classic car ownership today.

Dad and I took the car around 80 miles from home, ran beautifully no problems. However, once we reached the parking lot (big event had to follow line of cars to parking) I saw the temperature rise and then it overheated with steam from the coolant bottle cap. Pulled over as soon as I could and shut if off. I had noticed the cooling fans not running right before it blew. We waited a bit for it to cool down And finally was able to get it parked.

So after enjoying the event for 4 hours or so while the car cooled down we went back and did some testing:
- The fans come on with AC so they are working.
- Felt the airflow behind the fans and they are both spinning.
- Jumped the outerstat wires and the fans came on.

So we decide to try and make it home leaving the AC on so the fans stayed on. However, after getting on the interstate the car overheated and steam again. I pulled over quickly and shut it off. We got towed home after that.

I do not have the blue fan fail module, it is the fused leads. I believe all the other relays (besides rpm) are original or look it.

Some questions:

1. How likely has damaged been caused to the engine? And if so what?
2. I believe the thermostsat may be stuck closed because even at highway speeds with fans (because of AC being on) the engine still overheated. Is this a correct assumption?
3. I'm pretty sure the outerstat is bad because the fans weren't running when it overheated and they do with it jumped out. What else could be the problem?
4. Would an auto parts store (Advanced Auto etc.) be able to get these two parts and would they be correct? Or should I get them from Houston?

Any help is much appreciated.

[kings1527]

So I got my first slice of the downs in classic car ownership today.

Dad and I took the car around 80 miles from home, ran beautifully no problems. However, once we reached the parking lot (big event had to follow line of cars to parking) I saw the temperature rise and then it overheated with steam from the coolant bottle cap. Pulled over as soon as I could and shut if off. I had noticed the cooling fans not running right before it blew. We waited a bit for it to cool down And finally was able to get it parked.

So after enjoying the event for 4 hours or so while the car cooled down we went back and did some testing:
- The fans come on with AC so they are working.
- Felt the airflow behind the fans and they are both spinning.
- Jumped the outerstat wires and the fans came on.

So we decide to try and make it home leaving the AC on so the fans stayed on. However, after getting on the interstate the car overheated and steam again. I pulled over quickly and shut it off. We got towed home after that.

I do not have the blue fan fail module, it is the fused leads. I believe all the other relays (besides rpm) are original or look it.

Some questions:

1. How likely has damaged been caused to the engine? And if so what?
2. I believe the thermostsat may be stuck closed because even at highway speeds with fans (because of AC being on) the engine still overheated. Is this a correct assumption?
3. I'm pretty sure the outerstat is bad because the fans weren't running when it overheated and they do with it jumped out. What else could be the problem?
4. Would an auto parts store (Advanced Auto etc.) be able to get these two parts and would they be correct? Or should I get them from Houston?

Any help is much appreciated.

1) Tough to tell. If you can pull your dipstick and the oil looks like oil and not milky, then you're probably fine and the head gaskets are probably intact. You can also look for the plastic screen at the oil fill and see if it's intact, as well. If it is, you're looking pretty good. The PRV is a pretty stout and durable engine that can take significant abuse but it is aluminum and has its limitations.

2) Good possibility given the fact that you had the fans on with the AC but still overheated. Might as well replace, especially if you don't know the service history of the car.

3) I'd definitely swap in a new otterstat. $20 part.

4) I'd just go ahead and order through your favorite vender. You can cross reference a lot of parts on the car but these are low $$$ items and getting them from a DMC vendor ensures that you're getting the correct parts, especially when dealing with the cooling system. The vendors ship things out pretty quickly.

Keep us posted on developments.

[kings1527]

Here's a great website on EVERYTHING someone would need to know about a thermostat and how to test to see which position it's stuck in.

https://axleaddict.com/auto-repair/car-thermostat-troubleshooting

[DMCVegas]

Some questions:

1. How likely has damaged been caused to the engine? And if so what?

Depends upon the temperature as well as time length of time the engine was exposed to those higher temperatures. How high did the needle go?

Overheating doesn't always lead to instant head gasket failure, nor cylinder head warpage. However it can certainly cut the lifespan of the head gasket for sure. First thing to do would be to pull your oil filler cap and inspect the screen inside. How does it compare to this:

http://i1165.photobucket.com/albums/q593/DMCVegas/Oil%20Filler%20Necks_zpshovfl5ll.jpg



2. I believe the thermostsat may be stuck closed because even at highway speeds with fans (because of AC being on) the engine still overheated. Is this a correct assumption?

It is possible, but perhaps not quite guaranteed. Specifically because we don't know if you were low on coolant, had air in the lines, or if it was indeed a bad thermostat.



3. I'm pretty sure the outerstat is bad because the fans weren't running when it overheated and they do with it jumped out. What else could be the problem?

Nope. If you have an obstruction in the line due to any of the causes I just mentioned, there is no way that the hot water would ever have reached the Otterstat to trip the fans.

Then after you overheated, unless you burped the system up front too, you've got air bubbles that are not allowing proper coolant flow. That's also assuming you refilled with a 50/50 mixture of antifreeze to maintain the higher boiling temp, and didn't just add plain water back into the system.


4. Would an auto parts store (Advanced Auto etc.) be able to get these two parts and would they be correct? Or should I get them from Houston?

Stop right there. Do not just go out and buy new parts to throw at the car.

Probably best to go ahead and order OEM parts directly from a vendor. But in this case, you shouldn't even consider buying parts until you first diagnose if the ones you have are even bad.

In order to do that, you'll need to heat up some water in a saucepan on the stove, using a candy thermometer in order to keep tabs on the temperatures. DO NOT BOIL THE WATER! ONLY INCREASE TEMPERATURES TO THE NECESSARY LEVELS AS PER THE WORKSHOP MANUAL! Then expose the parts to the water to see if they function properly. Drop the thermostat in of course to see if it moves, and then partially submerge the Otterstat by it's electrical leads attached to alligator clips, connected to a multimeter to see if the thermal switch trips.

The first thing to do here is to perform a Pressure Test on the cooling system to ensure that you don't have any leaks. Then use the tester on your radiator cap. THEN you would move onto the testing of other parts. THEN you'd start buying new parts after you determined which ones were bad.

My two big concerns here personally are either a bad thermostat, or a leak somewhere such as a bad radiator cap which allowed coolant to escape and lower the fluid levels. But there are first ways to diagnose these parts.

Speaking of which, have you performed any recent work to any part of the cooling system?

Also, does anyone else here still shop at an actual auto parts store for car & truck parts? Between all the DeLorean vendors & Rock Auto, everything for my cars is purchased online at a significant savings.

[Nate88]

Thank you for all the replies. We will be doing these checks today.

Unfortunately the needle went all the way both times however I shut the engine off within 30 seconds if not faster. First time I didn't notice it until it was too late since I was watching traffic and pedestrians.

I will be buying any parts from a DeLorean vendor, just wasn't sure if they could have the same parts available at a local store.

I will update on what we find.

[Nate88]

4610646107

Checked the oil and looks ok. No sign of milkyness.

Tested thermostat with heated water in a bowl. It opened, but the water had to be boiling before it opened. The only thing we can think of is if somehow when driving air got into the system and that's what made it boil over the first time. That or the thermostat didn't open when it was in the car.

We didn't test the pressure because the steam/coolant only leaked out the cap when it boiled over. No visual signs of leak at any other part of the system. Can the system leak without dripping coolant? Also no signs of coolant leak when sitting for several days.

Before we set off on the trip, we checked the coolant bottle without opening it and it was in the middle between max and min.

I do have the original coolant bottle and I think the cap is too. Since we have the cooling system opened should this be swapped out for the stainless version?

[David T]

You are on the right track. Replace the O switch and the thermostat. Bleed the system of all air. Check the dipstick for any sign of moisture, it will appear as a white froth. If you did pop the head gaskets it will continue to overheat and you can confirm by testing the coolant for combustion gasses.

[cdrusn]

I would begin by replacing the cheap parts first. The radiator cap would be number 1, if it isn't holding 15# then your boiling point goes way down. I've seen caps that wouldn't even hold 5# but seemed o.k. when you screwed them in. Thermostat is cheap, replace it with one that opens up early. Make sure water pump is working, check to be sure the engine coolant hoses are getting warm that will tell you the thermostat is opening. Check for water pump leak through the weep hole. As far as air in the system goes, it will eventually bleed itself out after relatively short warm ups and cool downs. The coolant reservoir is at the highest point of the coolant system so air will naturally try to get to the top of the tank and bleed itself. I would be running a compression check just to make sure the head gasket hasn't all ready been blown. :race:

[Nate88]

Ordered a new O switch, thermostat, coolant bottle cap, and the gaskets and o-rings for the w-pipe. Hopefully this and a proper bleeding will fix the issue.

[Bitsyncmaster]

It's good your ran your AC to keep the fans running if the otterstat is bad but unless your AC was cycling a lot, that should have kept your engine cool. I would think your thermostat is bad or you had air trapped somewhere in the system. Did you happen to drive on any steep inclines around the time it overheat the first time?

[Nate88]

It's good your ran your AC to keep the fans running if the otterstat is bad but unless your AC was cycling a lot, that should have kept your engine cool. I would think your thermostat is bad or you had air trapped somewhere in the system. Did you happen to drive on any steep inclines around the time it overheat the first time?

Once we got on the interstate portion (98% of trip was 55 mph 2-lane) there were several overpasses and when getting off at our exit there was an incline but just typical 4-lane highway stuff. It did fine during those, it wasn't until we were going slower in the parking lot traffic that it heated up and fast

Last Sunday I took it on my favorite windy road that has many inclines and declines and curves and it did just fine. The very next day it did more low speed in town driving and some idling, no issues. Yesterday was the first I had driven since that in town stuff on Monday.

[Bitsyncmaster]

Once we got on the interstate portion (98% of trip was 55 mph 2-lane) there were several overpasses and when getting off at our exit there was an incline but just typical 4-lane highway stuff. It did fine during those, it wasn't until we were going slower in the parking lot traffic that it heated up and fast

Last Sunday I took it on my favorite windy road that has many inclines and declines and curves and it did just fine. The very next day it did more low speed in town driving and some idling, no issues. Yesterday was the first I had driven since that in town stuff on Monday.

I would lean to the thermostat failing then. It does not make sense you did all that driving and trapped air would be the cause.

[DMCVegas]

4610646107

Yeah, that's not good. The screen below is missing entirely, which means that the vehicle has probably overheated before. The screen is made out of a soft, translucent plastic that melts very easily when it overheats. It looks nasty, so people rip them out when overheating occurs. Which is also the only reason you'd rip one of those screens out.

Chances are, you've possibly got some internal damage now to the head gaskets. Especially given possible past history, and the temperature your engine reached.



Checked the oil and looks ok. No sign of milkyness.

I was told the same thing that the oil would look like "chocolate milk". Truthfully, I've no idea what kind of nasty chocolate milk other people drink, but it never looked like that to me. Did have gloopy chunks of coagulated oil though once it drained. To me it looked like rancid chicken fat.



Tested thermostat with heated water in a bowl. It opened, but the water had to be boiling before it opened. The only thing we can think of is if somehow when driving air got into the system and that's what made it boil over the first time. That or the thermostat didn't open when it was in the car.

If there was air trapped below the thermostat, it most definitely would NOT have opened because the hot water would never have been able to touch the wax to push it open. In this case, you're better off just buying a new thermostat anyways, and make sure it has a bleeder hole, or "jiggle pin" to let the steam bleed through so the water can hit and open it up.



We didn't test the pressure because the steam/coolant only leaked out the cap when it boiled over. No visual signs of leak at any other part of the system. Can the system leak without dripping coolant? Also no signs of coolant leak when sitting for several days.

Big mistake. You absolutely MUST pressure test the system.

Yes, the cooling system can leak without dripping coolant. Quick lesson: Matter has 3 forms: Solid, Liquid, and Gas. Or in this case, Ice, Water, and Steam. Pure water at atmospheric pressure freezes @ 32°F and boils at 212°F. Mixing the water with various other minerals and compounds can affect it's properties. In this case, antifreeze. Likewise if you can compact and contain a substance under a certain amount of pressure to prevent it from expanding, you can also alter it's physical properties. Such as LPG or Propane when stored in cylinders as a liquid, but when released they rapidly expand into a gaseous form.

So, between the 50/50 mixture of antifreeze and the physical restrictions we impose on the coolant solution, we have severely altered the properties of the water to now instead freeze @ -34°F and boil at 265°F. Once released from the confines of the system, the physical properties rapidly change again to a lower boiling point. So as soon as the coolant gets out, instead of dripping, it steams out and evaporates away. If you have a bad radiator cap this will certainly happen, and unless you use a clear drain hose, you'd never notice it.

If you have a leaking Y-Pipe behind the Water Pump, you could have a puddle of coolant sitting there, and never know it unless you specifically went to look for it.

That however is assuming an external leak. You still have to deal with internal leaks where the coolant may either collect in the engine oil, or enters directly into the combustion chambers. In either case, it boils off and is expelled with the exhaust. With a small enough leak that goes unattended, you won't even see steam in the exhaust. It's not until a catastrophic failure that occurs.


Before we set off on the trip, we checked the coolant bottle without opening it and it was in the middle between max and min.

Doesn't matter. If there was air in the system, it wouldn't have ever reached the thermostat.


I do have the original coolant bottle and I think the cap is too. Since we have the cooling system opened should this be swapped out for the stainless version?

It's always a good idea to upgrade, as well as replace that ancient cap. DeLoreans are great, and they're damn reliable cars. When properly maintained. We're dealing with 35 year-old, used cars now though. Certain parts are absolutely wearable, and NEED to be replaced like the radiator cap

[Nate88]

Thanks everyone for the replies.

We are planning to do a compression test tomorrow to see if head gasket failure. Crossing fingers they are good.

Is the screen something that should be replaced? I'm not sure if it was there before the trip or not. This is the first time it has overheated on me and I drove it around 1000 miles between last year and this before I bought it.

I have a new thermostat, otterstat and radiator cap on order. It sounds like it's a good idea to pressure test the system before we add coolant once we put in the new parts.

[Nate88]

Did a compression test. This was on a cold engine.

First test:
1= 140
2= 140
3= 130
4= 145
5= 140
6= 120

Second test:
1= 145
2= 145
3= 132
4= 150
5= 150
6= 130. Tested 6 a third time got 130.

Seems that 6 is the worst off followed by 3. How bad is it? Need new cylinder head gasket?

[DMCVegas]

Did a compression test. This was on a cold engine.

First test:
1= 140
2= 140
3= 130
4= 145
5= 140
6= 120

Second test:
1= 145
2= 145
3= 132
4= 150
5= 150
6= 130. Tested 6 a third time got 130.

Seems that 6 is the worst off followed by 3. How bad is it? Need new cylinder head gasket?

No, that is a compression test within the cylinders and combustion chambers. Overall those appear to be good :thumbup:, but you need to perform a compression test upon the Cooling System itself. In order to do that, you'll need a device which looks like this;

http://image.cpsimg.com/sites/carparts-mc/assets/classroom/images/pressuretester.jpg

You can either buy one, or just use one of those tool lending programs from an auto parts store.

The head gaskets not only keep the combustion chambers sealed and separated, they also do the same for the internal Lubrication and Cooling Systems as well. You could still have an internal leak between those two. You could also still have an external leak in another part of the system where you cannot see either, such as in the VOD. In order to test for this, fill the system and burp it. Then attach a Pressure Tester, and pump it up to about 14-15 PSI and let it sit for a couple of hours to see if you have a significant drop in pressure. THEN you'll know if your system has a problem.

If you're missing that screen, that means that your engine has probably overheated before. This is just the first time that it has overheated with *you*. It's not required that you replace it, just don't drop anything inside of the engine while filling it with oil. Perform the pressure test on your Cooling system and let us know the results.

[AugustneverEnds]

Most Autozones have a pressure tester with an attachment to fit the DMC's header bottle. You deposit $80 and it's refunded when you return it. Or of course you keep it for future use.

Compression test results are fine, pretty tough those little French pieces of aluminum!!

You are doing the right things and hopefully the cooling system pressure test will rule out any leaks.

[Nate88]

It is encouraging that the compression test results are good.

I understand the cooling system needs pressure tested however, we have it tore apart to test the thermostat and otterstat. Since I have those on order shouldn't I wait to perform the cooling system pressure test after I install the new parts?

[DMCVegas]

I would wait until after the new parts are installed, yes. No sense in doing twice the work when you don't have to.

You're doing great!

[Nate88]

I would wait until after the new parts are installed, yes. No sense in doing twice the work when you don't have to.

You're doing great!

Great! Thanks for the confidence!

One more question...

My coolant currently is green in the car. I could only find yellow or orange so I got 50/50 Prestone which I believe is yellow. Is it ok to mix?

[DMCVegas]

Usually a good rule of thumb is that you don't want to mix colors and/or brands. Especially when it comes to modern cars, and in particular General Motors vehicles. But unless it's DEX COOL, you're usually fine.

Prestone's universal coolant (which may appear as either Gold or Orange) is fine. HOWEVER, make damn sure you do NOT, under ANY circumstances use DEX COOL! Lots of problems with that stuff, especially silicone. That stuff will actually say DEX COOL on the bottle, and the bottle itself is Silver.

Anything else and you'll be fine. Even if you wanted to use another brand. So if you find a bottle of PEAK with the old green antifreeze in it, you'd be perfectly fine using that as well.

Also, when you pour the antifreeze out, make sure you hold the bottle sideways. It prevents the stuff from glugging on the way out and has a nice steady stream of fluid.

[David T]

The compression test is not conclusive, only indicative and the results seem OK. To be sure you didn't pop the head gaskets the only conclusive test is a combustion gas test on the coolant. Doing a pressure test is not conclusive either, you are only testing to 15 psi and usually that test not done hot. Or you can go by symptoms. If you always seem to be adding coolant and you don't see leaks, you don't seem to have enough power, it wants to overheat, you probably popped the gaskets. You would also see evidence on the spark plugs. You might see a milky foam on the dipstick. In a severe case you would get hydro-locking and it won't crank over because one or more cylinders would have coolant in them.

[Nate88]

The compression test is not conclusive, only indicative and the results seem OK. To be sure you didn't pop the head gaskets the only conclusive test is a combustion gas test on the coolant. Doing a pressure test is not conclusive either, you are only testing to 15 psi and usually that test not done hot. Or you can go by symptoms. If you always seem to be adding coolant and you don't see leaks, you don't seem to have enough power, it wants to overheat, you probably popped the gaskets. You would also see evidence on the spark plugs. You might see a milky foam on the dipstick. In a severe case you would get hydro-locking and it won't crank over because one or more cylinders would have coolant in them.

I haven't had to add coolant before and the car was running great before this happened. Spark plugs looked good and so did the dipstick, no sign of milkyness.

We are planning to do a pressure test on the cooling system once the new otterstat, thermostat, and radiator cap arrive and installed. We will see where that takes us. If that turns out ok, you still recommended the gas test?

[Nate88]

Usually a good rule of thumb is that you don't want to mix colors and/or brands. Especially when it comes to modern cars, and in particular General Motors vehicles. But unless it's DEX COOL, you're usually fine.

Prestone's universal coolant (which may appear as either Gold or Orange) is fine. HOWEVER, make damn sure you do NOT, under ANY circumstances use DEX COOL! Lots of problems with that stuff, especially silicone. That stuff will actually say DEX COOL on the bottle, and the bottle itself is Silver.

Anything else and you'll be fine. Even if you wanted to use another brand. So if you find a bottle of PEAK with the old green antifreeze in it, you'd be perfectly fine using that as well.

Also, when you pour the antifreeze out, make sure you hold the bottle sideways. It prevents the stuff from glugging on the way out and has a nice steady stream of fluid.


Did not get DEX COOL. It was labeled very well on the bottles. Good to know to stay far away from it.

[Nate88]

Received parts today, installed new otterstat, thermostat, and coolant bottle cap.

Poured new antifreeze in, bled the system at radiator and bleeder valve. Fans turned on properly and the temperature held just a hair above the first white hash mark on the gauge even with the front of the car facing the inside of the garage. Let it idle like that for 15-20 minutes or so and no issues. Didn't have time to drive or do a pressure test, but I do have the tester and will most likely perform one tomorrow and test drive.

So far so good!

[kings1527]

Received parts today, installed new otterstat, thermostat, and coolant bottle cap.

Poured new antifreeze in, bled the system at radiator and bleeder valve. Fans turned on properly and the temperature held just a hair above the first white hash mark on the gauge even with the front of the car facing the inside of the garage. Let it idle like that for 15-20 minutes or so and no issues. Didn't have time to drive or do a pressure test, but I do have the tester and will most likely perform one tomorrow and test drive.

So far so good!

Nice work! Sounds like you may have solved the mystery. When you do the pressure test, have the car and coolant at operating temperature. It's not uncommon to have leaks happen when the car is cold. When the coolant is at operating temp, it tends to expand and/or swell the hoses a bit and pinch off potential leaks. Nevertheless, you definitely want things buttoned up tight before you start.

[David T]

You must be very careful using a pressure tester on a motor suspected of having a blown head gasket. Keep a close eye on the pressure and NEVER let it get above 15 psi with the motor running. If you do have a blown head gasket, the combustion gases can leak into the cooling system and increase the pressure rapidly. The tester will not release the excess pressure like a radiator cap and you can blow up the radiator or hoses. Take the motor through several heating and cooling cycles. If you don't see bubbles in the header tank, the level in the header tank always returns to the same level when cold and it doesn't overheat, you should be OK. This doesn't mean you didn't do damage. It seems, on cars that got overheated, even if it seems OK, eventually you will need head gaskets. I guess a lot depends on how hot and for how long too. If you really smoked it you should change the oil too.

[Nate88]

So did some testing...

We did a pressure test on a cold engine up to 14psi it didn't hold and we got a leak somewhere in the valley, we are thinking the rear water pump hose or y-pipe. My dad who is a retired mechanic with 30 years experience doesn't understand why the engine should be warm to perform this test. He has always done it on a cold engine (never worked on DeLoreans though). So we warmed up the engine, put the pressure tester on the coolant bottle and only built pressure when revving (cooling fans on) and not very much. The valley leak seemed to have stopped during this test.

Did a ~6 mile test drive with stop signs and speeds up to 55mph and low as 25mph. Everything was great, fans didn't even need to kick on.

To be honest we are both at a loss. Everything seems to be running great and besides the possible self inflicted leak at first, none so far.

Thoughts?

[Bitsyncmaster]

Try your pressure tester on another car. It could be something leaking in the tester.

[kings1527]

The valley leak seemed to have stopped during this test.



Not sure why this car is any different but it's a common occurrence with DeLoreans. I'd just keep an eye on it and the next time you have the manifold off, be sure to tighten everything up on the back of the water pump.

[AugustneverEnds]

Not sure why this car is any different but it's a common occurrence with DeLoreans. I'd just keep an eye on it and the next time you have the manifold off, be sure to tighten everything up on the back of the water pump.

+1

My car was mysteriously losing coolant when the ambient temperature was cool (below 80F) I would top up the header tank and all would be fine. A few days later and it would be low again. I took the intake off tightened everything under there and it was fine. The only thing that makes sense is that when the coolant warmed up it swelled the rubber hoses and sealed off any tiny leaks and stayed that way until the coolant and ambient cooled down. Just keep monitoring the coolant level and you will figure it out.

[Nate88]

Did another test drive this time ~15 miles with the same variation of speeds. Even stopped by home in the middle to let it idle in driveway until fans came on, they did. Stopped for gas as well. No issues car ran great.

We'll have to take the intake manifold off and check everything at some point to be sure.