Engine overheating after thermostat change

[eseethal]

I need some help here please: I diagnosed a stuck open thermostat (it was really stuck open). No problems, the car only was heating up very slowly, temperatures were always in the normal range. I changed it to a new one from SpecialAuto. I had raised the rear end of the DeLorean up and bled/burped the system as recommended. So far, so good. Thermostat is closed, engine warms up quickly, thermostat opens, the lines to the cooler get warm, the cooler gets warm bottom to top. But when driving the temperature gauge quickly rises to the first orange mark and a little above that. I tried burping/bleeding several times, but I still see a quick rise in temperature under load. The fans kick in later, telling me that way that the temperature sensor gets a higher reading than the temperature switch for the fans. So is there still some air in the system trapped? Or the thermostat is not opening up completely. I put the thermostat in like the old one was (looks right when I check it in the parts manual).

Any ideas what I could try? The next step would be to try a new thermostat.

Many thanks..........Eugen

[DMC-81]

Hi Eugen,

You may still have some air trapped, especially under the thermostat. Does your thermostat have a check valve?

If not you can drill a 1/8" hole in the frame to aid bleeding. Like so:

45199

Then, raise the car again and repeat the bleeding process. Sometimes it takes more than one to remove the air.

[eseethal]

Dana, thanks, the old thermostat hat the little valve, but the new one did not. I will open up and drill this little hole.
Maybe this will fix my issues here. thanks........Eugen

[DMC5180]

Dana, thanks, the old thermostat hat the little valve, but the new one did not. I will open up and drill this little hole.
Maybe this will fix my issues here. thanks........Eugen

Also be sure to release air from the top bleed hose on the right side of the radiator.

[eseethal]

Thanks, yes, I bleed the right side of the radiator too (twice, really messy!). I even changed back the old thermostat but the engine still runs much hotter than before. It's like the waterpump is not working full. With an infrared thermometer I can measure temperatures: the lines to the radiator and the radiator itself are much cooler than the DeLorean temperature gauge says. I am an experienced mechanic and have bleed alot of rear/mideengine cars, but that really I cannot explain. Is it possible the water pump has gone bad?

Eugen

[DMCMW Dave]

Thanks, yes, I bleed the right side of the radiator too (twice, really messy!). I even changed back the old thermostat but the engine still runs much hotter than before. It's like the waterpump is not working full. With an infrared thermometer I can measure temperatures: the lines to the radiator and the radiator itself are much cooler than the DeLorean temperature gauge says. I am an experienced mechanic and have bleed alot of rear/mideengine cars, but that really I cannot explain. Is it possible the water pump has gone bad?

Eugen

Not likely. More likely you have air trapped in the radiator (you bled that) or the engine. That's really all it can be if it came on suddenly.

What is your thermometer reading on the 4 hoses right at the water pump?

Is the engine really as hot as you think it is? The gauge sender is at the back of the engine. Once in a while it will trap air (steam) and read much hotter than it really is. If that's the case, you run it enough at higher speed to clear it. But keep your thermometer on the hose going into the water pump to make sure it's really not overheating.

[eseethal]

Thanks, Dave! The thermometer reading is something in the range from 160-170 degrees. It's just the surface temperature, depending on the material these readings are not very precice. But I can feel these hoses are not really hot. That's why the fans are kicking in much later - I have to idle the engine for a while. I replaced the engine coolant sensor a couple of months before. The readings on the gauge were perfect then - 220 maximum. The radiator gets warm from bottom to top, so no air there, I am pretty sure. I'll try bleeding a couple of times again. It can't be much air in the system. When I pressure up the expansion tank manually with a pump, the level of the coolant does not change (as it would when air is in the system). And when I open the cap on the expansion tank, when the engine is really overheated, boiling cooling water would be the result. But there is not much pressure inside, just a little escape of air.

Eugen

[eseethal]

I have now been driving about 200 mls with this issue. I even once more change the thermostat to a new one, but still I get the high readings of my gauge.
- independend of outside temperatures, when I put a little load on the engine (accelerating, highway driving), the needle quickly sits a the first red mark
- I rule out trapped air, I have the auto bleeder system installed, the radiator gets warm evenly.
- when I come to a stop, the fans do not kick in - only when I let the car idle for a couple of minutes (telling me, that the temperature of the radiator and the hoses and the otterstat are not as high as the gauge wants me to believe)
- when I open the coolant bootle, not boiling water sprays into my face (which would be the case when the engine is really way above 220F)
- the needle of the gauge rests at the 100F mark (ignition on, engine cold, ext. temperature 70F). This is probably not correct, right?

So IMHO it is either the gauge or the newly installed temperature sensor. I will check the ground at the gauge (the ground pulls the needle down, the sensor voltage pulls it up, so a bad ground could lead to a higher reading, when I understand the principle right.)

Or it is a bad new sensor, that I had recently installed. The thermostat was stuck open so the engine probably ran too cool and the gauge readings where in the right range - now with the functioning thermostat the engine gets hotter and the readings are to high. Resistance values for the sensor would be great (ohms/fahrenheit) - then I could take ohm readings and compare it to the displayed temperaturr.
Any opinions on this highly appreciated.....

[David T]

If you got rid of all of the air in the system and it still gets hot and you still have air you may have blown your head gaskets. That would cause overheating and would push air into the cooling system. Confirm with a combustion gas test of the coolant. As for temps you can check with a non-contact infra red temperature gauge or stick a thermometer into the header bottle.

[eseethal]

Thanks, but I politely have to disagree: The cooling system does not pressure up, no signs of a blown head gasket, everything is fine so far, no air in the system. I also checked with an infrared temperature meter - the hoses are much cooler than the gauge wants me to believe. I am pretty sure it is either the sensor or the gauge. Even if the waterpump was not working or the thermostat was stuck (that would give me these symptoms of a hot engine and an not so hot radiator/hoses and fans not running), when I open the coolant bottle the coolant must be boiling. Coolant above 220F has to be boling if not under pressure.

Eugen

[DMCMW Dave]

I've seen bad gauges. Get one of those laser thermometers and measure the water temp coming out of the engine. Then calibrate your brain to the gauge or start changing parts


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[eseethal]

Thanks! There is no way to calibrate the gauge itself, I assume. Adding a resistor would not help as the gauge measures not linear, if I understood the principle correctly.

Eugen

[bfloyd]

Next time you do a flush and fill on your cooling system - invest in one of these "Air lift Radiator Coolant Vacuum Refill" tools. https://www.amazon.com/FJC-43610-Radiator-Coolant-Vacuum/dp/B00804HWOU/ref=sr_1_2?ie=UTF8&qid=1491330592&sr=8-2&keywords=air+lift+coolant+refill+tool

I bought one to use on my car. Makes the bleeding process a thing of the past. When your system is drained and ready to refill, all you do is insert the rubber cone adapter into the neck of the coolant bottle and hook up your air compressor. The way the fitting is made, the air passing through the fitting creates a venturi effect on the cooling system and sucks all of the air out of the system and puts it under vacuum. Once the hoses collapse (scary to watch) you close off the valve and watch the gauge for any system leaks. Once you verify that it holds a vacuum without any leak-down, you change out the venturi fitting for the refill fitting. Drop the hose of the refill fitting into a clean jug of antifreeze and open the valve. It literally sucks the coolant out of the jug and refills the system. NO air pockets at all. Because our cars have the radiator in the front and the engine in the back, it takes a little while to place the whole system under vacuum, but it works perfectly. You really need a decent sized air compressor to make it work right.

[David T]

While I also would recommend that, it is expensive and not everyone can afford it AND an air compressor. You can do a good job with a coolant system pressure tester. If you are certain the motor is not overheating and the head gaskets are OK, it would seem you just have an instrumentation error. If all of the connections are clean and tight then it will be either or both the sending unit and gauge. If the motor was ever overheated the sensor could have been "cooked". It is possible to recalibrate the temp gauge but you have to take the binnacle apart and bend things inside the gauge. Then test it with the motor running before putting everything back together. Verify your temps and make sure you got all of the air bubbles out. Bleed the rad by pressurizing the system and then loosening the small hose on the top, right corner. When cold the header bottle should not get less than 1/2 full.

[eseethal]

Thanks for your tips! The vaccum refill kit is an interesting concept! I have a pressure tester which makes bleeding easy. And when I build up pressure I can also see if there is air in the already bleeded system. When the coolant level sinks rapidly while pressuring up the coolant system there's got to be air somewhere. In my case, no air :-)
I'll try "recalibrating" the gauge and see how this works out.

Eugen

[DMCVegas]

I'm a bit fuzzy here on the concept of applying a vacuum to the cooling system in order to purge air out of it. Can someone give me an explanation on how that's supposed to work?

Also, if the sensor is bad, don't fool around with trying to "re-calibrate" the gauge to adapt to the bad sensor. If it's failing now, it may continue to get worse, and will one day go bad. So aside from constantly fiddling with the gauge to adapt to a bad sensor, when you do replace the sensor, you'll have to undo all of the modifications you did anyway.

It's frustrating enough to troubleshoot something when you're not running stock, and have to compensate for it in ways never intended. It's worse when you become the PO, and the new owner has to sort the vehicle out and is left scratching their head trying to figure out what you were doing as they remove mods and repair damage like this done to the car.

[SamHill]

Would the vacuum method stress hose clamps?

[eseethal]

Robert, thanks, I'll change the temperature sensor once again. The last time I did it I had the K-jetronic removed, to that was easy. It does look like a PITA to change the sensor with everything else (except the air filter) in place.

Eugen

[bfloyd]

Would the vacuum method stress hose clamps?

The only hoses I worried about were the two short ones on either side of the water pump, and the one on the back of the pump that connects to the Y-Pipe. Mine came out unscathed, and I don't have a leak anywhere.

[Josh]

A little late to chime in here but I have found over my ownership that the gauges are not to be trusted. The coolant temp gauge is the worst of them.

[opethmike]

A little late to chime in here but I have found over my ownership that the gauges are not to be trusted. The coolant temp gauge is the worst of them.

You must assume no maintenance has been done, unless you have receipts otherwise. Change the oil, make sure the proper DOT fluid is in the brakes, and make sure you remember that the factory design can not be improved upon.

[sdg3205]

A little late to chime in here but I have found over my ownership that the gauges are not to be trusted. The coolant temp gauge is the worst of them.

DeLorean gauges are the pinnacle of accuracy.

[Josh]

Awe man, who let you guys out.LOL