What temp thermostat??

[Jason94sport]

I'm doing a tune up on my 94 this weekend. When I had my B2 a way to free up HP was to change the stock thermostat out to a 180degree one. On the 4.0 does that still hold true. Which lower thermostat should I get, or should I just stay with the stock one.
Thanks

 

[Ray Lobato]

Jason,
Your Explorer was designed to run at a certain temperature, which is 195degrees. You computer is programmed for that parameter. Optimally you should put in the standard 195 degree thermpstat.

 

[Jason94sport]

So I cannot inprove performance by using a lower temp thermostat? I was able to do it on My Bronco II why will it not work with the X? Is it because it is MAS air? & the B2 was speed density?

 

[mdrut]

The computer uses several sensors to adjust the fuel/air ratio, one of these is a temperature sensor, by lowering the temp of the coolant, the computer is tricked into thinking it is still cold.The computer adjust for this and adds more fuel, there for... you are always running rich..more fuel than air...The design of the 4.0 doesn't allow for a rich gas mixture, it will bog the engine and decrease the fuel milage.....UNLESS, you get an aftermarket chip and a thermostat that is designed to run with that chip..This is the setup I'm running, fuel milage is OK and power increases in the mid and higher RPM ranges..hope it helps..

 

[MrShorty]

found this in a search of the site. thought I'd post as a reply instead of starting a new thread.

Originally posted by mdrut
The computer uses several sensors to adjust the fuel/air ratio, one of these is a temperature sensor, by lowering the temp of the coolant, the computer is tricked into thinking it is still cold.The computer adjust for this and adds more fuel, there for... you are always running rich..more fuel than air...
So... if the engine is running cold (or the computer thinks the engine is running cold) it richens the mixture. Is the converse true? If the engine is hot (or the computer thinks the engine is hot), does it lean out the mixture? Or, said another way, does the mixture vary inversely with engine temperature? Or does the computer ignore the temperature input (as far as adjusting the mixture) past a certain temperature?

 

[Texan01]

In short. Yes and to a point

This also holds somewhat true even on carbureted cars as well. the vacuum valves that operate the EGR and EFE valves open based on coolant temp.

The computer calculates the A/F ratio using the coolant sensor when it's in open loop (ie just started) when the O2 sensor gets warm enough then it'll calculate off that and the MAF/MAP sensor. but the computer also still looks at the coolant sensor just to confirm how much gas it should give.

 

[KEbert]

I heard that going to a 180 would effect emissions. So I just put another 195 in. If it is really hot where you are for a long period of time, like 4 or 5 months, then it might be worth it to put in a 180. But if not, then just keep the 195.