I know this has been talked about over and over and I know the correct design engine temperature is to be 210* with a 195* thermostat installed. I cannot convince our grandson that this is correct. He thinks that 210* +/- temperature that his jeep is running at is too high and wants to remove the 195* thermostat and replace it with 165* or no thermostat at all to make it run cooler. I know by putting a lower temperature thermostat 165* or no thermostat at all will not make it run cooler after it does reach temperature. How do I convince him that the 210* temperature is correct and anything lower than that will not be smart?
06 Wrangler TJ 4.0 engine temperatures
- Thread starter MRChiefE7
- Start date
The thermostat only controls the low temperature side of a cooling system, the high side is controlled by the entire systems ability to cool water. Water needs time to cool in the radiator. When the thermostat is closed the fan pulls outside air across the radiator and cools the water. If you lower the thermostat's temperature it remains open longer and the radiator doesn't get time to cool the water. With the thermostat being open longer the water’s temperature continues to rise as do engine temps with no “cool” water to bring it down.
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What makes him think this?
These engines are designed to run at a specific temperature for emissions, power and fuel efficientcy purposes. Trying to make the engine run cooler may trick the computer into staying in an open loop state meaning that it may be dumping more fuel into the engine than necessary. It's kind of the equivalent of running with the choke engaged if he's coming from a carburetor perspective.
Is there a problem he's trying to solve? Aside from the perception of it running too hot?
You've told him, sometimes people have to make mistakes for themselves. I'm sure people try to convince you of things from time to time that you don't buy and you don't listen, it's the same deal.
Tell him if the Jeep does not get up the the specified temperatures it can kill his mileage on short trips because the temps guide the air fuel mix set by the computer and it will be running rich a lot longer then it should. The rich mixture can also kill the cat if there are constant short trips. Computers have set points for a reason.
My other son's F-150 was having a temp signal issue and the dam thing sooted up the O2 sensors and set off codes.
Three equal Jeeps parked in the Mojave Desert one with 195 deg, the other two with 165 and no stat will be all operating at the same temp within 15 minutes.
My other son's F-150 was having a temp signal issue and the dam thing sooted up the O2 sensors and set off codes.
Three equal Jeeps parked in the Mojave Desert one with 195 deg, the other two with 165 and no stat will be all operating at the same temp within 15 minutes.
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Rubicon John
TJ Enthusiast
Tell him it’s not water, the coolant mixture will not boil until it’s quite a bit warmer. Nothing to worry about. The engine is supposed to run at 210deg F
The boiling point of 50/50 coolant at 18 PSI is approximately 270F. Lose all of that pressure through a leaking radiator or whatever and it will boil at around 226F.
Edit: At 10k feet altitude with that same 18 PSI cap, the boiling point of coolant (either 50/50 or water) is about 9 to 10 degrees lower than at sea level.
Edit: At 10k feet altitude with that same 18 PSI cap, the boiling point of coolant (either 50/50 or water) is about 9 to 10 degrees lower than at sea level.
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Give it a go. Pick measuring variables, record baseline and the difference, make a conclusion.
I never understood this American mentality to bla bla bla each other back and fourth till veins start to protrude on forehead, instead of getting straight to the point and figuring it out.
I never understood this American mentality to bla bla bla each other back and fourth till veins start to protrude on forehead, instead of getting straight to the point and figuring it out.
As OP stated:
"wants to remove the 195* thermostat and replace it with 165* or no thermostat at all to make it run cooler"
"210* temperature is correct and anything lower than that will not be smart"
What are you not tracking?
Tell your grandson to register here and we'll set him straight on how things work on a TJ. He is not being stupid, he is just ignorant of how such things work and why the TJ was designed to run at 210 degrees. Older cars ran fine at lower temperatures, newer cars and our Wranglers run far more efficiently and better at higher temperatures like 210.
Brianj5600
TJ Expert
TJRick
TJ Enthusiast
Small block Fords were using a 195 degree thermostat since the 1960s.
There is nothing special about the TJ. By design, all modern engines run hotter than they used to. Believe it or not, it is actually better for an engine to run as hot as possible - without overheating of course.
Can't give a precise answer but there's no benefit to it running that much cooler so you might as well install the correct 195 degree thermostat to get it up where the engineers designed it to run at. Not to mention the PCM is programmed around the correct temperature, not 190.
Brianj5600
TJ Expert
At 210 degrees, the ECM is already pulling timing under all conditions. Any efficiency gained by higher temperatures are not only negated, but efficiency is reduced. Add the air charge temperature and the ECM is pulling more timing from an already overly conservative timing table.
My ECM is not stock. Cooler combustion chambers allow more cylinder pressure with out knock. That is why aluminum heads can run higher a compression ratio on the same octane fuel.
I hated my 4.0 when I bought my Jeep. It was a total dog. It would not keep up with traffic on hills. Just working on the tune has made a big difference. It pulls the Tennessee hills on the interstate without losing speed now. Cooler water temps is part of the fix.
My ECM is not stock. Cooler combustion chambers allow more cylinder pressure with out knock. That is why aluminum heads can run higher a compression ratio on the same octane fuel.
I hated my 4.0 when I bought my Jeep. It was a total dog. It would not keep up with traffic on hills. Just working on the tune has made a big difference. It pulls the Tennessee hills on the interstate without losing speed now. Cooler water temps is part of the fix.
TJRick
TJ Enthusiast
I don't know if you are right about that or not, but I do know that the older carbureted engines did the exact opposite.
A ported vacuum switch was screwed into a coolant jacket that monitored coolant temperature. If it sensed coolant temperatures were reaching 220, it would switch the distributor timing source from ported to manifold vacuum. This would add timing, which would make the water pump and fan turn faster to help cool the engine.