Sudden high temp on gauge.

[Timebender]

I had the oddest thing happen today while out. I had taken the car to go get some groceries, and the engine heated up to it's normal 220 on the gauge (which in reality is more around 185 according to a laser reading). For those that don't know already, I have a mid-80's 350 Chevy engine from a Vette.
So, like normal, while driving it ran just a tad below that mark, and at any stoplights it runs at or just a bit above it - and of course the fans, well, one big fan comes on - the smaller one had been out a while and I disconnected it so it wouldn't keep tripping the fan breaker. But even on hot days, the big fan always does a decent job of keeping things in check.

So after hitting Target, I run over to a Carl's Jr and after ordering, I'm waiting in line - and the temp looks fine. As I pull up to the window, after being in line about 10 minutes, I notice the gauge has jumped to just below the red. It seemed like it just climbed rapidly.

So I shut off the engine while waiting at the window for my order, about a couple minutes, then fire it up, and now the temp is down around the 200 mark. As I started driving, it went back to 220, and while at a light for a few minutes, it stayed there.

When I got home I let the car idle in the driveway for another 5 minutes and it didn't happen.

Any ideas?

Bad otterstat not turning on the fan and being intermittent? Or? I'm pretty sure i heard the fan on when it started to climb on the gauge as I had my door open when in the line. Maybe just a wonky gauge anomaly?

Maybe it was from being behind another car pretty close in line and the heat from their exhaust was causing an issue?

[DMC5180]

If the gauge sensor wire were to Go intermittent open the needle would point straight up 12:00.

I'm sure your fan is loud enough that you would hear it. If you say you could hear it run. Then I would lean towards a stuck thermostat or an air pocket in the system that found its way to the sender. I don't know where the sender is usually located on a 350.

I assume you've checked your coolant level.

[Timebender]

Possibly an air pocket - but I'm sure I bled it a while ago after putting in a new thermostat, but one can never be too sure. The sensor is on the side of the block above close to the spark plugs.

And I checked the fluid when I got home to make sure. But I'm thinking, and it might be slightly possible (?) that when in line, less than a foot away from the cat in front of me, the fan was pulling in hot air.. ?

As it seemed after that and when I left, all was back to normal. For now.

Meanwhile I'll be keeping an even closer eye on it.

[Bitsyncmaster]

If the gauge sensor wire were to Go intermittent open the needle would point straight up 12:00.

My testing shows an open the gauge would not move off the normal cold engine position. If the sensor or wire shorts to ground the gauge would point almost strait up. The cold sensor is normally about 2.5 Kohm and normal engine temp about 100 ohms.

[Jonathan]

I would run some tests under conditions you choose to figure it out. Or eliminate things anyway. Intermittent problems aren't always easy to find.

First test I would do would be to run the engine and let it get up to temperature. Do this parked in your driveway, somewhere flat and with room around the car for air to flow. Confirm the cooling fans come on as they should and watch to see the temperature come back down and the fans shut off. Let it idle some more, fans kick on, engine cools down, repeat. That would test the cooling system for normal conditions.

Next test I would do would be to try the same thing but this time try and limit the source of fresh air. Maybe do it while you're parked in the garage and the front of the car is up in there without a lot of fresh air circulating. The car should still be able to cool itself down like this.

After that, you might go looking to try the same drive thru test you did inadvertently the first time. Or you could rig something up at home to test it like that while you control the situation and won't fear a big mess (or circus). You could use another vehicle you have to be running right in front of your D and simulate the drive thru overheating or lack of fresh, cool air. See what happens and shut it off whenever you get past a point that makes you nervous.

The nice thing about running the first two tests is that you'll have seen what the cooling system does under normal conditions and will know exactly where on the gauge the needle points when the fans kick on or off. I don't doubt that trying to cool the car down using hot air from the car in front of you caused the problem. The rad is just a heat exchanger in the simplest terms and if the air on the side that is supposed to be cooler isn't, the hot coolant on the car side doesn't have anywhere to give off that heat.

Check the coolant levels of course beforehand, like mentioned. An air pocket is a possibility too and those first tests will help rule that out for you. I know your systems are modified slightly with the engine swap, but testing it without jumpers and as close to being in real conditions is the best way to go IMO. It at least lets you see exactly what happens with your car in the conditions you'll be using it. Jumpers can help in pin pointing the issue to an otterstat for example, but seeing the car perform (or fail) "as is" is the best test to put the issue to rest.

[DMC-81]

If you find that you are not able to repeat the issue, I bet the hot car in front of you overwhelmed the cooling capacity.
I'd replace /fix the smaller fan as perhaps that one helps the system perform during situations like the one you had.

I remember my V8 Fiero had a similar issue in drive thru lanes and long traffic lights. I think I rigged up a switch to turn on the stock Fiero fans manually for those occasions as I was nervous about overheating the car. Of course, a better solution would have been to get a bigger radiator/ fans. But it worked and I never overheated it.

[David T]

Replace the thermostat. I have seen then get stuck. They don't make them like they used to, they seem to fail a lot more often.

[Timebender]

Replace the thermostat. I have seen then get stuck. They don't make them like they used to, they seem to fail a lot more often.
Good idea - I did replace it last Summer when the one in there just gave put one hot summer day when I just happened to be looking for a parking space at the local weekly car show. The overflow hose blew out and spewed fluid EVERYWHERE...

Cheap and easy fix, and I'll also test the other things again in the driveway per the other suggestions here.

And this, btw, is why the DeLorean community is so AWESOME.

[DaraSue]

Replace the thermostat. I have seen then get stuck. They don't make them like they used to, they seem to fail a lot more often.

Seconding this. I got random temp spikes that would go away after sitting for half an hour when I first bought the car (although it only ever did it at freeway speeds, not while idling). It went away with a new thermostat, but I ended up having a host of other issues due to corrosion and sediment in the cooling system (fairly certain that's what gummed up the thermostat it came with). If you see any rust in your coolant, that's something to watch out for.

[David T]

When you replace the thermostat make sure it has a "jiggle pin". It is important. It allows you to bleed air out of the system. If it doesn't have it you can still use the thermostat, just drill a 1/16" hole in it to pass air. Better to get the right one with the pin in the first place though. The gasket is a cut, square "O" ring. It fits AROUND the thermostat, NOT under or over it. Only use the correct parts.

[DMC5180]

When you replace the thermostat make sure it has a "jiggle pin". It is important. It allows you to bleed air out of the system. If it doesn't have it you can still use the thermostat, just drill a 1/16" hole in it to pass air. Better to get the right one with the pin in the first place though. The gasket is a cut, square "O" ring. It fits AROUND the thermostat, NOT under or over it. Only use the correct parts.

He has a Chevy 350 installed. The thermostat may not have the square O-ring like the PRV does.

[David T]

You are right, of course. I mention it for the majority of the owners in this forum because they do. As for this particular conversion, he knows what he has and has to do. He *could* have a bad thermostat, that info is still valid for him.

[Timebender]

So I tried several things - put more coolant in, no luck Replaced the thermostat, and at first it did get liquid to the otterstat, but the fans still wouldn't come on until 220 - and so I let the engine cool off for a while, removed the thermostat housing plug to see if the thermostat was working, and it was, but not a lot of liquid would come up from the engine. So I put it back on, let the engine cool down again, put more coolant and water in the radiator, tried again, released the plug a little to let any air out- it did for a while, engine got really hot, fans didn't come on till 230 now.
So I left the engine off to let out any more air from the plug.
Replaced the otterstat, tried again, and noticed the hose above the thermostat was getting hot, but it was cool in the otterstat pipe. So I took off the hose and checked for blockage - none. Took out the thermostat and then took the plug out to watch, and this time the water just stayed in the engine - never came up and out.

I'm guessing it's a bad pump - it does spin on the outside just fine, but typically a bad water pump would leak before it just stops.. unless the impeller inside just came loose.

Thoughts?

[opethmike]

Shot in the dark - Take the cap off the coolant bottle and watch for if the coolant circulates?

[DMCMW Dave]

Shot in the dark - Take the cap off the coolant bottle and watch for if the coolant circulates?

That's exactly the test. Take the cap off (cold), start the engine, and look inside the bottle where the bleed hose attaches. You should be able to see water spraying out of the hose. With some design metal bottles you can't see it, but you can stick your finger in there and feel it (not to hot when you first start the car, but DO NOT do this if it's been running a while.

[David T]

The impeller could have come loose, the blades could be worn off, the belt could be spinning it backwards, all things you should check. You have to make sure all of the air is out, you may need to drill a 1/16" hole in the stat so air can pass. Check that the suction hose has a spring in it so it can't collapse under vacuum. The otterstat switch should be at a lower temp than the thermostat so once the thermostat opens and the hot coolant hits the switch the fans will go on.

[Timebender]

When you replace the thermostat make sure it has a "jiggle pin". It is important. It allows you to bleed air out of the system. If it doesn't have it you can still use the thermostat, just drill a 1/16" hole in it to pass air. Better to get the right one with the pin in the first place though. The gasket is a cut, square "O" ring. It fits AROUND the thermostat, NOT under or over it. Only use the correct parts.

I ended up getting a 180 thermostat, one of the nicer Standt ones - I'll have to see if it has the jiggle pin, and of not, I'll add a little hole on my press.

[Timebender]

The impeller could have come loose, the blades could be worn off, the belt could be spinning it backwards, all things you should check. You have to make sure all of the air is out, you may need to drill a 1/16" hole in the stat so air can pass. Check that the suction hose has a spring in it so it can't collapse under vacuum. The otterstat switch should be at a lower temp than the thermostat so once the thermostat opens and the hot coolant hits the switch the fans will go on.

I actually took the spring out of the hose that goes from the engine to the otterstat pipe, as it was badly rusted and collapsing inside, plus the tube is pretty old and worn looking. I took it to a local parts store - Carquest, and they couldn't find a match. Any idea where i can get a new one? They had one that was close, but it was much longer, and when I try to go around the engine to get to the metal pipe, it crimps at the curve.

[Timebender]

So I did everything that was recommended - added water into the engine until it bubbled up with the thermostat off, drilled a hole (1/16th) in the thermostat, ran water down the return pipe until the radiator overflowed, then put a hose in the radiator and ran the engine. This time it ran cool for a while, then the fan came on at the 220 mark (that was good), but the temp just kept climbing anyway, the fan having little to no effect.

Tomorrow I'll do an oil change and see if that does it - and yes, replaced the radiator cap too.

I'm baffled at this point. At least I know my water pump is working.

[David T]

So I did everything that was recommended - added water into the engine until it bubbled up with the thermostat off, drilled a hole (1/16th) in the thermostat, ran water down the return pipe until the radiator overflowed, then put a hose in the radiator and ran the engine. This time it ran cool for a while, then the fan came on at the 220 mark (that was good), but the temp just kept climbing anyway, the fan having little to no effect.

Tomorrow I'll do an oil change and see if that does it - and yes, replaced the radiator cap too.

I'm baffled at this point. At least I know my water pump is working.

The oil change should not make any difference. Make sure the suction hose is not kinked or collapsing when it gets hot. Get a spring in it.

[DMC5180]

Please post a photo of your engine installation with good visuals of the hoses to the water pump.

Did you pull the pump to actually look at the impeller?

Also when the otterstat had the fan running did you physically feel the return line for noticeable temperature difference? I ask because I was surprised how much lower the return side is when the fans are running and the engine is idling. Low rpm water flow really allows the radiator/ fans to pull the heat out if the coolant.

In my case the otterstat side was to hot to touch while the return side felt like ambient temp.

[Timebender]

Last night, I ran the car again and it was still getting too hot - after running water through it with the hose on and in the radiator, putting water and some coolant in the engine before putting on the thermostat - which I drilled. So I shut it off for a bit to cool it down, and wondered if the plastic overflow was too full. So I removed it, and noticed the hose from the metal tank never was actually doing anything, as I had connected it directly to one of the nipples, assuming there was a hose inside connected as well.

NOPE.

So I got the hose inside the plastic tank out (which it came with and I never noticed), drilled a hole just a little smaller than the hose to fit tight, and then put the tank back in and connected the new clear hose to the metal tank, and followed that with filling it about 1/3rd.

Ran the car again, fan came on at around the 235 mark (which is actually about 220 -maybe less as it's a 180 degree otterstat) - and still got too hot.
So let it cool down again then put it back in the garage. But, I did notice a little green coming into the clear hose, with lots of air bubbles.

This morning I thought I'd run it again so more air would come out, and noticed the plastic tank was almost empty. So I filled it up about half way, fired up the D, and waited. It took longer than before to warm up (good), and then the fan came on just below the 220 mark, which is about 195, and stayed on for about 20 minutes as I watched the temp drop to 180 on the gauge - and the fan shut off. Took about 10 minutes to climb back up and just below 220 on the gauge, the fan came on. But this time it seemed to stay - never climbed, and I think I waited about 10 minutes but it didn't drop again either - which I think is somewhat normal.

After shutting off the car and going in the house, I did go back out and heard a blooping sound, to find that there was more air going into the plastic tank.

So overall it's a success.

But I would like to get the cap off the metal tank at some point and see if it needs to be filled more as well - however no matter how I try, it just doesn't want to come loose - either by twisting or pressing and twisting.

Any ideas would be appreciated, and I want to thank everyone who chipped in with advice and help!

http://dmctalk.org/attachment.php?attachmentid=53550&d=1505932856http://dmctalk.org/attachment.php?attachmentid=53551&d=1505932857http://dmctalk.org/attachment.php?attachmentid=53552&d=1505932858

[DMC5180]

Sounds like you just needed to work air out of the system. Do you know if there is a high point air bleeder on your radiator? I assume you have a custom radiator. On the OE radiator their is a bleed hose on the Passenger side which doesn't alway work like it should. You end up pulling the little hose loose just enough the let the air escape. One of the aftermarket suppliers actually incorporates a bleed screw on the top of the RH radiator end tank.

[opethmike]

Having owned a few mid and rear-engine cars, I can with good experience say that it is worth the money to get an Air Lift vacuum:

http://www.tooltopia.com/uview-550000.aspx?utm_source=google&utm_medium=cpc&utm_campaign=paid_search_google_pla&adpos=1o2&scid=scplpUV+550000&sc_intid=UV+550000&gclid=EAIaIQobChMIk5-nxsG01gIVxoeyCh0KfwnjEAQYAiABEgJnnPD_BwE

[Bitsyncmaster]

It's normal when the thermostat opens the coolant is flowing through the cold radiator and then the thermostat closes because of that cold return coolant. It keeps doing that with shorter cycles until the radiator heats up to normal temp.

The otterstat has about 8 deg. C of hysteresis which is about 15 deg. F

[Timebender]

It's normal when the thermostat opens the coolant is flowing through the cold radiator and then the thermostat closes because of that cold return coolant. It keeps doing that with shorter cycles until the radiator heats up to normal temp.

The otterstat has about 8 deg. C of hysteresis which is about 15 deg. F

Oh that's interesting and good to know!

[Timebender]

Sounds like you just needed to work air out of the system. Do you know if there is a high point air bleeder on your radiator? I assume you have a custom radiator. On the OE radiator their is a bleed hose on the Passenger side which doesn't alway work like it should. You end up pulling the little hose loose just enough the let the air escape. One of the aftermarket suppliers actually incorporates a bleed screw on the top of the RH radiator end tank.


Yep - amazing how much trouble that can cause. As far as the radiator, maybe? Or it's stock out of something bigger - the cap is on the passenger side at an angle between the top and side, so it makes it difficult to fill it "all the way" to the top, and fluid likes to spill out most anytime I take it off unless it's low.

And as far as the metal tank - I haven't found any bleed screw on it - seems to be sealed tight and still trying to figure out how to get the lid off.

[Timebender]

Having owned a few mid and rear-engine cars, I can with good experience say that it is worth the money to get an Air Lift vacuum:

http://www.tooltopia.com/uview-550000.aspx?utm_source=google&utm_medium=cpc&utm_campaign=paid_search_google_pla&adpos=1o2&scid=scplpUV+550000&sc_intid=UV+550000&gclid=EAIaIQobChMIk5-nxsG01gIVxoeyCh0KfwnjEAQYAiABEgJnnPD_BwE
Oh that's swanky.

[David T]

Oh that's swanky.

To use it you must have a large air compressor so you can pull a hard enough vacuum. It will only work on a system that is completely empty. You get one shot at it so you need to fill a bucket with 2 gallons of anti-freeze and 2 gallons of water and do it all in one shot. You should still pressurize the system afterwards and bleed any residual air out but it does work well. A very nice tool to have but not essential. You can do a proper job with just the pressure tester but it will take more time.

[Ron]

+1 on thermostat


The sensor is on the side of the block above close to the spark plugs.

It's probably not the problem, but the fan switch should be in the head, not on the side of the block. The correct port is between cylinders 6 & 8, a little higher than the spark plugs. (If the heads have been swapped, it's between 1 & 3 and OK.)
Check that a heavy duty connector (like OEM, usually has dark brown holder) is being used in any case, especially if it has headers!