Overheating (only) under load

[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?