I have a 98' XJR with the factory engine oil cooler. In theory, can I pull the guts of the thermostat out and just reinstall the plate to maintain pressure? I'm not trying to reinvent the wheel, but I do live in Florida and it gets quite hot in the summer. I also don't know how often the thermostat opens up either and is the oil that's in the cooler just staying stagnant for long periods of time.... I don't know, but I would like to keep the fluids circulating at all times if my initial question is feasible. I'm in the middle of doing head gaskets at this time and it was just something to think about while the car is currently down.

 

The thermostat helps to keep the oil at a suitable minimum operating temperature and to hasten warm up from cold.

Both are very desirable features.

There would be no gain from defeating the thermostat.

 

The ecu depends on the engine being at the right temperature for fuel mapping. I suspect that removing the oil thermostat could be bad just like removing the water thermostat. And besides, the lubrication design depends on the oil being at the expected temperature.

 

. . . and the AJx engines are so sensitive to overheating that modifying the coolant system is probably not a good idea.

A better idea is to modify the temperature idiot gauge with the the RealGauge product.

About XK8 / XKR / XJ RealGauge - TheJagWrangler

 

I knew that the ECU saw the engine oil temp not only because of the temp sensors in front of the lower oil pan, but because our Autologic displays it in volts like the coolant. I just wasn't aware of the actual mapping adjustments as a result of engine oil temps. I suppose It makes sence though, the water temps clearly changes maps, so does trans oil temps, so why not engine oil temps. Not that it makes a difference to me, but does anyone know when the engine oil thermostat opens up?

 

see the engine repair course #168 pdf kindly posted
up by MotorcarMan. it's in there.

btw, the colder thermostat that i run keeps the needle
1.5 marks below the middle when cruising at 80mph.

still good enough to get into closed loop and achieves
maximum heat when required.

the temperature gauge actually means something now
because if it creeps up from 1.5 marks below the middle,
then something is up ... like crawling in traffic.

 

Sorry for the delay in response. Just a little clarification about my post in question is about a factory installed engine oil cooler. There's a engine oil thermostat installed in the upper oil pan (or bed plate) that deflects oil to the oil cooler in front of the A/C condenser. I was just wanting to know while the heads were off if it was ok to gut/modify the oil thermostat because I wasn't sure how long the oil sits stagnant inside that cooler without flow and also what temperature the oil thermostat opened at. I did look for the engine repair course and wasn't successful on my phone. I'll get on a real computer and checkout some more specs.

 

It's still a bad idea.

Why do you want to over cool the oil?

 

For the same reason they over cool the engine. Lack of knowledge of thermodynamics.

We all know an overheated engine or overheated oil is BAD; So, the cooler we can get it the better, right?

 

Fed by the myth that lower coolant temps equals more horsepower.

 

I doubt anyone really believes that. I assume it is the assumption that it is somehow better for the long term reliability of the engine.

 

My goal wasn't a search for more hp. The car has 234K miles on it with the original engine and I don't think it would stand up to anything other than what it was given since day one unless it was rebuilt entirely. I am unaware just how often the oil cooler thermostat opens up to let 'fresh' oil flow thru the cooler. However, I have done enough digging and I have answered my own question. The oil diverter valve begins to open between 217* - 225* F
(103* - 107* C) and is fully open at 246* F (119* C)
It was just a food for thought question while the top end and front end of the engine is apart. I suppose for me to know the real response to my question would either entail me to have an oil temperature gauge setup or use a scantool and learn how to translate the factory oil temperature sending unit that reads volts and turn it into Fahrenheit.

 

I wonder what the temperature of the oil on a NA Xj8 is under highway load on a hot day? I suspect it is about that temperature.

 

The next piece of documentation is JTIS. The resistance to temperature
relationship of the sensor is documented there.

 

I run a colder thermostat because I would rather not bake
hoses, wiring and plastics any more than required. Cooler
temperatures also prevent precipitating compounds out
of the coolant. Or at least that is what Toyota engineers
and others have found. There is a sweet spot and it is
below 205*F.

180*F at cruise is not unreasonable.

It enters closed loop as fast as any other thermostat since
the closed loop threshold is below opening temperature of
any thermostat.

 

Yeah, I was thinking about checking JTIS concerning the volts to temp translation. I'll get around to that soon.

I'd also agree about running the colder coolant thermostat...that is until you get the check engine light about 'Regulating thermostat below threshold'. There's just too much heat and too much plastic under the hood. The aftermarket replacement radiators are crap, the fuel injector shrouding covers bake and already the sensor connectors are breaking like a cheap Chinese watch. At least we don't have it as bad as the 04'+ XJ's. Those years of plastic components are even thinner than ours.

 

Well, first of all, the plastic parts and hoses and so on that are NOT in the "inner loop" of the cooling system will be running HOTTER with a lower temperature thermostat. Why? If the inner or engine loop of the cooling system is running at lower temperature, then more heat is being extracted. The outer loop through the radiator has a constant removal of heat. Therefore , the radiator loop will be running at a higher temperature while removing more heat from the engine.

I suspect, but have no data to support, that a lower temperature engine thermostat will reduce the effectiveness of the intercoolers, which is marginal as it is. Again, if you are removing heat from the engine, the heat load on the radiator is greater and the radiator water will be running hotter.

This is just another area where intuition instead of science will get you in trouble.

 

Very well put.

Thanks.