Colder Thermostat for 4.2

[JHogg419]

I have been searching for a colder thermostat for the 4.2L. I am not finding anything on the forum or the internet. Just to make sure, no one makes one at this point correct?

[djthumper]

You don't want a colder one. Your mileage will plunge.

[chevycrew]

These newer engines are designed to run at a certain temperature for complete fuel combustion. Lower engine temps will hurt the combustion resulting in reduced fuel mileage. If you have cooling issues, then there are other areas that can be improved.

[v7guy]

The 4.2 doesn't benefit from a colder stat like the good ole SBC. The failure mode for our thermostat is to fail open, so you can get the effect by just putting in a shit thermostat, as it happens though, the result is abysmal gas mileage and no added power gain.


If you're looking for more power the intake and heads on the newer motors make a good bit more and there has been some good ole turbo setups. This isn't really the forum for that though. Our engines make plenty of power for our purposes. That's not to say 4-500hp isn't a hoot

[JHogg419]

I've been reading some about gas mileage. I see people say change their plugs, clean their TB and change the thermostat. I thought that is where they were going with that. Thanks guys. I have 3.42 gears in now and I am looking into what to do to do to replace them. I can't seem to figure out why I need the computer reflashed. I have replaced gears on older trucks with no issues. Still researching though. Thanks everyone.

[DustinC1989]

Speedometer correction, flashing the computer isn't required beyond that

[Trail X]

I've been reading some about gas mileage. I see people say change their plugs, clean their TB and change the thermostat. I thought that is where they were going with that. Thanks guys. I have 3.42 gears in now and I am looking into what to do to do to replace them. I can't seem to figure out why I need the computer reflashed. I have replaced gears on older trucks with no issues. Still researching though. Thanks everyone.

2005- TBs have three vehicle speed sensors. One is before the diff, on the drive shaft, two are on the front wheel hubs. They spin at different velocities, therefore the computer must know the diff ratio in order to understand that your front wheels aren't spinning at a different speed than the rear wheels.

[navigator]

I've been reading some about gas mileage. I see people say .... change the thermostat.......

Jason and Steve explained it, the reason folks change their Tstat is because they start failing open causing the engine to run cooler than it should. If your needle isn't straight up at 210 then you likely have a weak Tstat. The gauge is a dummy gauge and isn't an exact representation of temperature so the temp will be running a good bit cooler than it shows.

Changing the Tstat isn't as straightforward on our platform as most. Most folks change the sender at the same time because they are hard to get to.

[bgwolfpack]

Think...Goldilocks Zone

[JHogg419]

I've been reading some about gas mileage. I see people say .... change the thermostat.......

Jason and Steve explained it, the reason folks change their Tstat is because they start failing open causing the engine to run cooler than it should. If your needle isn't straight up at 210 then you likely have a weak Tstat. The gauge is a dummy gauge and isn't an exact representation of temperature so the temp will be running a good bit cooler than it shows.

Changing the Tstat isn't as straightforward on our platform as most. Most folks change the sender at the same time because they are hard to get to.

Yeah Mine is running straight up. Just trying to squeeze a little more out of it. I should just be happy I am getting average 15mpg. It is just bone stock 4.2L 3.42 4WD. I thought I should be getting better. As I read the Mileage Thread, it seems they are all over the place.

Jarrod

[navigator]

the thing that helps me most with my gas mileage is my scangauge II. Having it show my immediate MPG and AVG helps me modify my driving habits.

[onebigburb]

Bring old post back. You guys say there is no power to gain from lower t-stat and motors are designed to run what I consider hot. Now heres my questions in all of this. The t-stat was built in one unit so you couldn't change it affecting emissions stuff, however the old rule to thumb the more COLD air you can ram down an engines throat the more power you make. So if you have colder t-stat colder intake manifold = more power? So then there must be code somewhere in vcm for these trucks to want 200*ish on temp. shouldn't something like hp tuner be able to adjust that? Personally I could care less about emissions ( I live in no emission zone for a reason). My theory is if you machine the t-stat houseing out and install another t-stat that fits thats 180*ish. Do a vcm flash for it then there should be no negative reasults only positive colder engine & more power.