thermostat/exhaust gas temp ?

[krakhedd]

Hi guys,

'01 4.0 AW4, Borla cat-back, DIY K&N, IAT relocate, TBS, bored cat, 180*F thermostat.

With the decrease in back pressure in my exhaust, I wonder how much more performance I could eke out by using the stock 195*F thermostat? Hotter exhaust is easier to move, but how much hotter would it be with the higher thermostat?

Thanks!

 

[LazarusMJ]

Hi guys,

'01 4.0 AW4, Borla cat-back, DIY K&N, IAT relocate, TBS, bored cat, 180*F thermostat.

With the decrease in back pressure in my exhaust, I wonder how much more performance I could eke out by using the stock 195*F thermostat? Hotter exhaust is easier to move, but how much hotter would it be with the higher thermostat?

Thanks!

Yes, hotter EG moves quicker but cooler combustion chambers produce more power by keeping the incoming air cooler. Seems to me that you have a good setup.

 

[PapaPump]

i was under the impression that hotter chamber temps would be more efficient...cooler intake air has a denser charge which means more oxygen in the cylinder head...but more compression and thus heat makes for better power output. and there is a lot of info on here saying that an iron head will produce more power because the aluminum extracts heat from the combustion chambers too well.

 

[old_man]

Hotter combustion temps cause a significant rise in NO emissions. That is why the EGR valve was invented. By feeding back a small amount of exhaust into the intake the combustion temps are lowered. It also helps prevent PING. While hotter combustion temps may help power a bit, they come with a cost.

 

[krakhedd]

Well, I went ahead and installed a 195* today anyway. It seems to have better throttle response, more power partial-throttle, even maybe a little more WOT. I can't tell about mileage, cuz well, I have been dipping WAY far into the throttle all day today :d

Even though everything you've said is correct, OldMan (I'm not trying to avoid a dispute, I just know that what you said is sound science, besides your reputation here being that you know your shit), but I wonder if maybe my stock ECU just plain runs better with the hotter temps?

The other thing I thought of is that, since I have my hood vents, the engine compartment never really gets hot, keeping the intake charge nice and cool. Even if the whole engine block is roughly 15* hotter. That, plus my custom K&N, basically.

 

[old_man]

My comments were based solely on combustion temp issues, not related to thermostat values. You should be running a 195 degree thermostat. IIRC, that is the factory spec.

 

[DeftwillP]

Even if the whole engine block is roughly 15* hotter.

The thermostat doesn't actually function to keep the engine at the specified temp. It serves to keep the coolant from flowing until it meets that temp.

 

[PapaPump]

i have been running a 160 thermostat since may because kragen didnt have anything else. i live in a temperate zone so the temperature is always between 50-70 or so and this thermostat shouldnt even be stocked here. anyhow, i think i run a little rich because of it but i havent had any sensor problems. what i have heard is that the whole system is set up to run at 180+, so i should swap that thing out. anyhow, i feel that my part-throttle feels weak, especially at low RPMs and that my gas mileage isnt very good (14-19 with 235/75r15s and 3.07s). i am going to swap back now because the temperature will be getting slightly lower and kragen probably has the right one by now, so i will keep you posted on the seat-of-the-pants thing.

 

[Dr. Dyno]

Hi guys,

'01 4.0 AW4, Borla cat-back, DIY K&N, IAT relocate, TBS, bored cat, 180*F thermostat.

With the decrease in back pressure in my exhaust, I wonder how much more performance I could eke out by using the stock 195*F thermostat? Hotter exhaust is easier to move, but how much hotter would it be with the higher thermostat?

Thanks!

The only advantage you'll get by switching back to a 195* t'stat is better heater function in the winter months. Otherwise your set up is good as it is.

 

[krakhedd]

Glad to know - I did, after all, refer extensively to your web site for lots of my info :d Especially the IAT relocate...