Overheating (only) under load

[TripleZeroFilms]

Hey guys,

I've been dealing with a tricky issue as of late and figured it might be worth throwing it out to the think-tank.

THE PROBLEM:

I've just recently repaired my A/C system after fighting it for the last year. Yay! But I now have a new problem: overheating. I live in GA and it is pretty warm here during the summer. If I start driving my car, completely cold, MAX A/C, my engine temp will begin hitting 220 within ~20min (and will rise forever unless action is taken). If I bump it down to NORMAL A/C the temp will drop to ~195 and slowly climb back up to 220+. If I again drop it to A/C OFF (i.e. hot box in the summer), the dial will yet again fall only to rise back up. Turing on the heat at full blast will result to the temp dropping to normal levels and remaining there so long as it is engaged. As soon the heater is turned off, up goes the temp. All this occurs only while driving.

ADDITIONAL INFO:
New water pump and hoses throughout.
New thermostat.
Both of my (original) fans are working properly.
Radiator is NOT plastic.
There is NO coolant leaking/being expelled from the car at any point, no matter the temp.
Coolant level is full.
The system is fully bled.
While at idle, A/C OFF, NORMAL A/C, or MAX A/C, the temperature is perfect.
There are NO bubbles in my coolant tank.

My current thoughts:
Faulty (new) thermostat?
Engine timing/vacuum advance issue?
Radiator plugged?

I am open to all thoughts and suggestions on the topic!

[DMCMW Dave]

My current thoughts:
Faulty (new) thermostat?
Engine timing/vacuum advance issue?
Radiator plugged?

I am open to all thoughts and suggestions on the topic!

Usually really weird overheat issues are head gaskets on the way out. But don't go there first. That problem is typically accompanied by expelling coolant from the cap.

If it seems to get hot way to fast (per the gauge), I've often found that means that there is air in the engine and the sender is fooled by steam. If this is the problem the engine won't seem to be all that hot. But if you have had it on the road at speed that should be long gone. Burp the thermostat bleeder again anyway.

When it is overheating like this, how hot is the line coming from the radiator at the right front lower?

I'd bleed the radiator (again, but trust me on this). Open the small hose at the upper right end of the radiator and let the air out. Coolant header bottle cap should be off (open). Coolant can be cold.

The only difference between regular A/C and MAX A/C is that hot water is circulating in the heater core, so when you switch from MAX to normal you've introduced a second radiator of sorts Aka the heater core, and it was full of relatively cool water.

If this doesn't do it, I'd check for a plugged radiator but that's actually pretty hard to test for. What radiator is it? You said "not plastic", is it one of the aftermarket brass ones? How old?

Air in the radiator will act exactly like a plugged radiator. I've honestly never seen a plugged radiator in person, although I've heard of a few.

One more check - do this cold if you have the metal header tank. With the cap off the tank run the engine. Stick your finger in the tank and see if you feel water coming into the tank from the small hose that goes to the back of the engine. If you don't, the tee at the back of the engine is blocked and you are getting air trapped in the engine. That hose bleeds the engine block.

[Bitsyncmaster]

I would check the current draw on your fans. If you have fused jumpers, bypass the fan circuit breaker. I have seen one set of OEM fans draw 10 amps and others (my old fans) draw more than 15 amps each. Maybe your fan circuit breaker is popping open since running the AC keeps the fans running.

If the fans are not the problem, I would suggest you try one of the cooling system flush kits.

[TripleZeroFilms]

Usually really weird overheat issues are head gaskets on the way out. But don't go there first. That problem is typically accompanied by expelling coolant from the cap.

If it seems to get hot way to fast (per the gauge), I've often found that means that there is air in the engine and the sender is fooled by steam. If this is the problem the engine won't seem to be all that hot. But if you have had it on the road at speed that should be long gone. Burp the thermostat bleeder again anyway.

When it is overheating like this, how hot is the line coming from the radiator at the right front lower?

I'd bleed the radiator (again, but trust me on this). Open the small hose at the upper right end of the radiator and let the air out. Coolant header bottle cap should be off (open). Coolant can be cold.

The only difference between regular A/C and MAX A/C is that hot water is circulating in the heater core, so when you switch from MAX to normal you've introduced a second radiator of sorts Aka the heater core, and it was full of relatively cool water.

If this doesn't do it, I'd check for a plugged radiator but that's actually pretty hard to test for. What radiator is it? You said "not plastic", is it one of the aftermarket brass ones? How old?

Air in the radiator will act exactly like a plugged radiator. I've honestly never seen a plugged radiator in person, although I've heard of a few.

One more check - do this cold if you have the metal header tank. With the cap off the tank run the engine. Stick your finger in the tank and see if you feel water coming into the tank from the small hose that goes to the back of the engine. If you don't, the tee at the back of the engine is blocked and you are getting air trapped in the engine. That hose bleeds the engine block.

I will attempt to bleed again from both ends. That being said, I have done so many times in the past few days. I should also mention that I have an auto-bleeder on the rear of the car (which can be closed manually). Also, as I haven't been burping with the coolant cap off, I will try that. What is the advantage of removing it before bleeding?

As for the temperature, it doesn't get hot particularly fast, but it creeps up over time (20 minutes or so at speed). This makes me wonder if it could be steam related, as doesn't that typically result in the temp increasing quickly?

Regarding the radiator, it was installed by PJ Grady in 1996 (via the previous owner). The invoice only lists it as "Brass Radiator" with a part number of 100486G. Next time I get the engine up to temp I will check the hose leaving the radiator, but I will have to do so by hand as I don't have a temp gun on hand for specific readings.

[David T]

I will attempt to bleed again from both ends. That being said, I have done so many times in the past few days. I should also mention that I have an auto-bleeder on the rear of the car (which can be closed manually). Also, as I haven't been burping with the coolant cap off, I will try that. What is the advantage of removing it before bleeding?

As for the temperature, it doesn't get hot particularly fast, but it creeps up over time (20 minutes or so at speed). This makes me wonder if it could be steam related, as doesn't that typically result in the temp increasing quickly?

Regarding the radiator, it was installed by PJ Grady in 1996 (via the previous owner). The invoice only lists it as "Brass Radiator" with a part number of 100486G. Next time I get the engine up to temp I will check the hose leaving the radiator, but I will have to do so by hand as I don't have a temp gun on hand for specific readings.

From your description of the symptoms it would seem using the heater core to help cool the motor off is just enough "extra" to cool the motor. This tells me the radiator is not transferring enough heat. That can be because of a couple of things. If there is any air in it, it will reduce it's transfer capacity. Loosen the small hose on the top, right corner and let out any air. Next, if there is ANYTHING interfering or blocking the inlet duct you will not get enough air. Is there a license plate or anything mounted near the inlet to the rad duct? Next, you did say both fans are working but check if the fans are firmly attached to the motor shafts. If they are loose they may be connected but not spinning at full speed and drawing enough air through. Also check that both fans are blowing in the correct direction, from front to back. Finally, it is possible the air side is plugged up with debris either the condenser core, the rad or between them so enough air isn't getting through. I would also check the timing and mechanical and vacuum advance to be sure they are all set correctly and working.

[Flash66]

DaveDMCMW is spot on. If running the heater at max cools the temp at speed, it's air in the system. No doubt. First and foremost, change your thermostat! Second check for flow into the bottle from the rear of the engine for blocked T. Now to bleed a pesky air pocket out of your car, this method works every time and uses a little science. Get a long 10" thin funnel (Walmart auto) and put it in the tank with a rag or two around the neck to keep it in place and somewhat sealed in. Then (in a DeLorean) jack up the "rear" of the car as high as you can and start it. This will help the air in the system to rise to the highest point. Keep adding coolant through the funnel with your bleeder open until it's burped as much as possible. The funnel helps push the coolant through with gravity. Next, jack up the front of the car and repeat the process with the upper RH hose at the top of the radiator. I promise this is your fix.

[David T]

DaveDMCMW is spot on. If running the heater at max cools the temp at speed, it's air in the system. No doubt. First and foremost, change your thermostat! Second check for flow into the bottle from the rear of the engine for blocked T. Now to bleed a pesky air pocket out of your car, this method works every time and uses a little science. Get a long 10" thin funnel (Walmart auto) and put it in the tank with a rag or two around the neck to keep it in place and somewhat sealed in. Then (in a DeLorean) jack up the "rear" of the car as high as you can and start it. This will help the air in the system to rise to the highest point. Keep adding coolant through the funnel with your bleeder open until it's burped as much as possible. The funnel helps push the coolant through with gravity. Next, jack up the front of the car and repeat the process with the upper RH hose at the top of the radiator. I promise this is your fix.


Actually the easier way is to use a coolant system pressure tester and loosen the small hose on the top right side of the rad to get the air out of it and the bleeder on the thermostat housing to get the air out of the motor. Any left after that will work it's way out. If you keep getting air you have leaks and/or a blown head gasket.

[Flash66]

Any left after that will work it's way out.

By that time he will have blown his head gaskets. The point here is that air is trapped and it's already overheating under load. The engine isn't going to keep taking the abuse before his heads warp or worse. At this point it's best to get all of the air out NOW and not wait for it to work itself out. Using a pressure tester just introduces more air and creates pockets between the engine rear and the heater core ( hence running the heat at full to cool the engine)

Using the science of elevation, combined with gravity, heat and natural pressure (and adding water, not AIR) is the most effective solution to expelling the air from an engines cooling system. Research, Infiniti and Mercedes, I guess I'm the first to introduce this method to the DeLorean community and you'll thank me for it.

How I learned of this: My Infiniti QX4 was suffering from the same exact issue. The dealer told me I'd need to spend 4-5k to repair my engine because they've tried everything and the symptom would keep returning it did keep returning under load especially in hot weather. Running the heat at full blast would start bringing the gauge down from H almost instantly and they swore my head gaskets were the problem. They've bled and bled to no avail. Using this method not only cured the problem, but also confirmed for me to always be your own advocate when it comes to your engine. Thanks to Ferrari and Mercedes forums, I was able to save myself a boat load of money and tell the dealer to kiss my ass.

Be persistent. When you feel all of the air is out, do it again anyway.

[David T]

By that time he will have blown his head gaskets. The point here is that air is trapped and it's already overheating under load. The engine isn't going to keep taking the abuse before his heads warp or worse. At this point it's best to get all of the air out NOW and not wait for it to work itself out. Using a pressure tester just introduces more air and creates pockets between the engine rear and the heater core ( hence running the heat at full to cool the engine)

Using the science of elevation, combined with gravity, heat and natural pressure (and adding water, not AIR) is the most effective solution to expelling the air from an engines cooling system. Research, Infiniti and Mercedes, I guess I'm the first to introduce this method to the DeLorean community and you'll thank me for it.

How I learned of this: My Infiniti QX4 was suffering from the same exact issue. The dealer told me I'd need to spend 4-5k to repair my engine because they've tried everything and the symptom would keep returning it did keep returning under load especially in hot weather. Running the heat at full blast would start bringing the gauge down from H almost instantly and they swore my head gaskets were the problem. They've bled and bled to no avail. Using this method not only cured the problem, but also confirmed for me to always be your own advocate when it comes to your engine. Thanks to Ferrari and Mercedes forums, I was able to save myself a boat load of money and tell the dealer to kiss my ass.

Be persistent. When you feel all of the air is out, do it again anyway.

Even using your method you can't get ALL of the air out. It takes several heating/cooling cycles and the system can handle it. What it CAN"T handle is the large initial amount of air from filling the system. My method (and it is used by all of the venders too) is quicker and more through. The problem is if you keep finding yourself having to get air out. That means more is getting in and no amount of bleeding is going to get it all out and keep it out. I consider the auto-bleeder a Band-Aid and if you need it to keep your motor from overheating the problem should be found and fixed.

[Flash66]

Actually using this method will get all of the "trapped" air out and doesn't take several cycles. Your old method will. You are right about finding a problem if there's a leak, but that would be obvious. The air is trapped and all I'm suggesting is regardless of how it's been done in the past, there's always a better way and this is it. The dealer I spoke of used a pressure tester also and guess what? His air bubble location is unique to this situation and requires tackling it from another perspective. He already bled it several times and it's not working. I'm not saying you're wrong David but a little science can make all of the difference.

[David T]

Actually using this method will get all of the "trapped" air out and doesn't take several cycles. Your old method will. You are right about finding a problem if there's a leak, but that would be obvious. The air is trapped and all I'm suggesting is regardless of how it's been done in the past, there's always a better way and this is it. The dealer I spoke of used a pressure tester also and guess what? His air bubble location is unique to this situation and requires tackling it from another perspective. He already bled it several times and it's not working. I'm not saying you're wrong David but a little science can make all of the difference.

Having bled more than a few cars, Deloreans included, you never get ALL the air out. Some of it is dissolved in the cold coolant and it takes several cycles to get it out. Using the pressure tester to force the air out under pressure gets most of it. You are not "adding air" so much as increasing the pressure of the air above the coolant and getting the air out faster. I also use an "evacuator" which first puts the entire cooling system under a vacuum and then draws coolant into all of the "trapped" areas. It speeds up the process but is not essential. What I do consider essential is the pressure tester. Not only does it force out air it also helps to locate any leaks. Leaks are the main source of air. As the system cools it can pull air in besides the fact that as coolant escapes air comes in to replace it. Pressure testers are not expensive and if you can't afford one you can rent them.

[Flash66]

Ok David. My last bit of info is to make sure it's bled with the heat valve open.

[PJ Grady Inc.]

It's nice to see someone else besides me having a "quid pro quo" with David! Atta boy "Flash66" atta boy ;)


Ok David. My last bit of info is to make sure it's bled with the heat valve open.

[David T]

It's nice to see someone else besides me having a "quid pro quo" with David! Atta boy "Flash66" atta boy ;)

Take a number, there is a LINE of people! I think Claude made #1!

[PJ Grady Inc.]

I was refering to rational people David if you get my drift!


Take a number, there is a LINE of people! I think Claude made #1!

[Flash66]

It's nice to see someone else besides me having a "quid pro quo" with David! Atta boy "Flash66" atta boy ;)

Ha! It's more like "quo pro quid" in this case. I give, and he fights to maintain the "status quo" of only tit for tat in return. I know of a great place he can stick that pressure tester and pump away! 😤

[DMC5180]

Now Now, Play nice.

Good Info regardless of which method is used.

[Flash66]

Now Now, Play nice.

Good Info regardless of which method is used.

Ah, it's all in good spirit. I sincerely only meant it to be humorous. David's great.

[David T]

Ah, it's all in good spirit. I sincerely only meant it to be humorous. David's great.

I am an equal opportunity offender, I will post with rational AND irrational posters. I may have strong views but they are based on experience. The reader is left to decide what is good for themselves. I ask, does Rob lift the car in the air to bleed the coolant system? I ask knowing the answer but better to hear it from him.

[Jonathan]

Not sure where the OP is with bleeding air out of the system, but one thing that came to mind even when it was only his first post so far in this thread, was to reconfirm the assumptions made.

Like if it just doesn't add up, double check what you already listed as being fine. Mostly whether the cooling fans are indeed working as they should, as Dave McK mentioned. You might need a helper to confirm if the circuit breaker or something else is causing them to cut out.

Our cars take a lot of heat (groan!) for being poorly designed, but my opinion is that the cooling system works fairly well if it is all working as intended. Assuming the test day isn't one with crazy hot temps outside, our cars can maintain a reasonably cool engine temp just with the air flow under the car and past the rad without the fans actually coming on while you are at highway speeds.

If that doesn't even happen on your car, maybe the water pump isn't pumping as well as you think it is? You mentioned it was replaced, maybe something is blocking the flow or limiting it in someway? Maybe some of the shipping plugs or packaging is still on it? Just something else to consider if your attempts to bleed the air isn't getting you anywhere.

[Flash66]

You're probably right. Rob most likely does not lift rear of the car in the air to bleed. BUT you're views are solely based on experience of knowing only one way to do it. Ferrari, Mercedes, Infiniti procedures all state to raise either the front or rear of the car (depending on engine/radiator location) to allow air to reach the highest point in the system to be expelled. Why? Because the engines are expensive and this method helps to evacuate as much air as possible from the system at the time of the procedure to prevent any damage from residual pockets causing overheating. My strong position in this thread is also based on experience and worked to where all other conventional methods failed. I would bet my last dollar that if Rob had this particular car in his shop and the issue remained post conventional bleeding, after reading about my experience he'd have the rear of the car at a 45 degree angle because he's OPEN minded.

Also FWIW, water pumps either pump or they don't. There's no in between. AND if running a heater wide open cools the system almost immediately, it's 99.9% certain there's air trapped in the rear of the engine which is bypassed by opening the hot water valve.

[PJ Grady Inc.]

"If there is any air in it, it will reduce it's transfer capacity. Loosen the small hose on the top, right corner and let out any air." Spot on David.
That is a often overlooked item that will cause the system to run hot. Even a couple ounces of air here is enough to cause a drastic increase in temperature and is the first item I'd check given the available information. We did a lot of work to this car in 1996 and the whole cooling system was replaced at that time and the relays updated. Obviously after 19 years the whole system needs going through again as is being done here. Sure sounds like trapped air somewhere and the radiator is a prime suspect here.
Rob


From your description of the symptoms it would seem using the heater core to help cool the motor off is just enough "extra" to cool the motor. This tells me the radiator is not transferring enough heat. That can be because of a couple of things. If there is any air in it, it will reduce it's transfer capacity. Loosen the small hose on the top, right corner and let out any air. Next, if there is ANYTHING interfering or blocking the inlet duct you will not get enough air. Is there a license plate or anything mounted near the inlet to the rad duct? Next, you did say both fans are working but check if the fans are firmly attached to the motor shafts. If they are loose they may be connected but not spinning at full speed and drawing enough air through. Also check that both fans are blowing in the correct direction, from front to back. Finally, it is possible the air side is plugged up with debris either the condenser core, the rad or between them so enough air isn't getting through. I would also check the timing and mechanical and vacuum advance to be sure they are all set correctly and working.

[PJ Grady Inc.]

While I don't routinely lift the back end for bleeding I am well aware of the benefits of doing so as air always seeks the highest point in a cooling system. I have done this with problematic cars in the past. Thanks for the "open minded" compliment as I believe you should listen to all viewpoints if you want to arrive at the best solution to a problem. David probably feels that way too but you always have to allow him the last word;) I learned that a long time ago. Right David?


You're probably right. Rob most likely does not lift rear of the car in the air to bleed. BUT you're views are solely based on experience of knowing only one way to do it. Ferrari, Mercedes, Infiniti procedures all state to raise either the front or rear of the car (depending on engine/radiator location) to allow air to reach the highest point in the system to be expelled. Why? Because the engines are expensive and this method helps to evacuate as much air as possible from the system at the time of the procedure to prevent any damage from residual pockets causing overheating. My strong position in this thread is also based on experience and worked to where all other conventional methods failed. I would bet my last dollar that if Rob had this particular car in his shop and the issue remained post conventional bleeding, after reading about my experience he'd have the rear of the car at a 45 degree angle because he's OPEN minded.

Also FWIW, water pumps either pump or they don't. There's no in between. AND if running a heater wide open cools the system almost immediately, it's 99.9% certain there's air trapped in the rear of the engine which is bypassed by opening the hot water valve.

[David T]

You're probably right. Rob most likely does not lift rear of the car in the air to bleed. BUT you're views are solely based on experience of knowing only one way to do it. Ferrari, Mercedes, Infiniti procedures all state to raise either the front or rear of the car (depending on engine/radiator location) to allow air to reach the highest point in the system to be expelled. Why? Because the engines are expensive and this method helps to evacuate as much air as possible from the system at the time of the procedure to prevent any damage from residual pockets causing overheating. My strong position in this thread is also based on experience and worked to where all other conventional methods failed. I would bet my last dollar that if Rob had this particular car in his shop and the issue remained post conventional bleeding, after reading about my experience he'd have the rear of the car at a 45 degree angle because he's OPEN minded.

Also FWIW, water pumps either pump or they don't. There's no in between. AND if running a heater wide open cools the system almost immediately, it's 99.9% certain there's air trapped in the rear of the engine which is bypassed by opening the hot water valve.

I disagree with this. If using the heater is enough to help cool the motor I say it means air is trapped in the radiator reducing it's ability to transfer heat. The small added transfer the heater is doing is just enough to do the job. On the Delorean trapped air in the heater core seems to be a non-issue, it gets out. I understand different cars have varying methods of bleeding air and what works for one does not necessarily mean it works for others or is even necessary. We will agree to disagree but using a pressure tester is a "tried and true" method and works just fine (at least on Deloreans when done correctly). BTW raising the rear of the car won't help if the trapped air is above the lowest obstacle meaning if you don't raise the car enough air can still stay trapped in the radiator.

[Flash66]

I disagree with this.

Of course you do.




We will agree to disagree.

Fair enough.

[Jonathan]

Also FWIW, water pumps either pump or they don't. There's no in between.

I don't agree, but I won't waste my time trying to help you understand.

[Flash66]

I don't agree, but I won't waste my time trying to help you understand.

Maybe I should have worded it differently. They either pump or piss. My bad.

[Rokkinlen]

Hey guys,

I've been dealing with a tricky issue as of late and figured it might be worth throwing it out to the think-tank.

THE PROBLEM:

I've just recently repaired my A/C system after fighting it for the last year. Yay! But I now have a new problem: overheating. I live in GA and it is pretty warm here during the summer. If I start driving my car, completely cold, MAX A/C, my engine temp will begin hitting 220 within ~20min (and will rise forever unless action is taken). If I bump it down to NORMAL A/C the temp will drop to ~195 and slowly climb back up to 220+. If I again drop it to A/C OFF (i.e. hot box in the summer), the dial will yet again fall only to rise back up. Turing on the heat at full blast will result to the temp dropping to normal levels and remaining there so long as it is engaged. As soon the heater is turned off, up goes the temp. All this occurs only while driving.

ADDITIONAL INFO:
New water pump and hoses throughout.
New thermostat.
Both of my (original) fans are working properly.
Radiator is NOT plastic.
There is NO coolant leaking/being expelled from the car at any point, no matter the temp.
Coolant level is full.
The system is fully bled.
While at idle, A/C OFF, NORMAL A/C, or MAX A/C, the temperature is perfect.
There are NO bubbles in my coolant tank.

My current thoughts:
Faulty (new) thermostat?
Engine timing/vacuum advance issue?
Radiator plugged?

I am open to all thoughts and suggestions on the topic!

I have the same symptoms. Do you remember what your problem ended up being and what the solution was?