I thought I would collect this information and put it in such a form that an admin or mod could move it over to the FAQ if they see fit..

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Why would you want to use a lower temperature rated thermostat?

Engines get hot.. Duh.. A hotter engine is more likely to allow detonation of your air+fuel mix BEFORE spark is applied than a cooler one.. The cooler the engine, the less likely you will get pre-detonation. This is the reason to use a cooler thermostat, but there are two major reasons why folks would consider such..

1. Eliminate or reduce pre-detonation, a.k.a. 'pinging'..
2. Advance ignition timing in a safer (cooler) environment..

When would you want to use a lower rated temperature thermostat?

Only when you have adjusted ('tuned') the PCM to curve fuel would you be reaping any benefit from using a 180* 'stat.. Until you 'tune' the engine, you are wasting fuel, and layering crap on your o2 sensors and cats, which will shorten their lives.. The engine may give the impression of running better, but that's just what rich engines do- they feel smoother.. Don't be fooled, you're robbing yourself of power..

The PCM is looking for an operating temperature of 195*, and when it's having a hard time achieving that, it adds fuel.. Why? Cooler air+fuel charges are harder to ignite, so, it adds more catalyst (fuel) to make the explosion more possible..

Expectations in power while using a lower temperature rated thermostat:

gotta look at this from two vantages....

With a TUNE, curving fuel and advancing spark-

economy: look for similar fuel economy as you had with the OE 195* thermostat, or, just a little less economy..

performance: look for gains in power production and improved throttle response.. you may pick up as much as 5~10 ponies using a 180* 'stat, and it's all because of advancing timing on a denser air+fuel load... Think of it something like this- the piston moves north, squeezing the a+f into a volatile little ball, and hits it with spark to make it explode.. On an engine that is warm(er), it is only safe to do so just after the piston reached top dead center, and starts heading south- otherwise, you could have pre-detonation, which is the explosive force pushing against the mechanical revolution of an engine.. Bad stuff, yo.. But, if you can hit the a+f load with spark either RIGHT at top dead center of the pistons travel, or SLIGHTLY before the piston hits TDC, (to give the piston time to complete it's travel and reach north just as the BOOM REALLY starts to expand), you've effectively INCREASED compression of the engine in comparison to an engine that hits spark AFTER the piston starts heading south.. The smaller, tighter, denser that little ball of a+f is, the more powerful it's explosion, the more power you put to the ground, and again, it can be somewhere between 5~10 ponies worth across eight cylinders...

WITHOUT a tune:

Economy: look for a drastic fall off in economy while using a cooler 'stat without a tune to support it. The engine will squirt excess fuel in effort to make the BOOM more likely to happen (avoid misfires)..

performance: look for richer conditions which will make your engine run smoother, but less powerfully.. contrary to popular opinion, a rich engine DOES NOT produce more power.. It produces less than the 'perfect' a/f mix of 14.7:1... venturing to either side of that 14.7 will result in loss of power..


Why do our trucks come with a 195* thermostat?

emissions standards. The warmer the engine, the more 'burn off' of excess gases..

Why not use a 160* thermostat instead of a 180* thermostat, if the 180* is better than a 195*?

there is a point somewhere between 160* and 180* that your PCM will start tossing codes your way.. You will get a P1281 "engine too cool for too long".. Even without a 'tune', your engine likely won't kick this code with a 180*, but it certainly will with a 160*..

there is also a temperature point where your engine is most efficient at burning all that fuel, and it can only advance timing so far too.. The point of maxing the advance is achieved with the 180*. Any reduction in operating temperature beyond that point, is going to have adverse reaction in emissions.. which, in that extreme, will have adverse reaction in performance too.


Will using a 180* thermostat really make the engine run cooler?

Yes.. and, No..

Your engines operating temperature is going to be dictated by the overall health and configuration of your entire cooling system. The volume of coolant, the velocity and volume of coolant movement, and the surface area of your heat exchange have more impact on your operating temperature than the 'stat does.. However.. Your 'stat opening sooner allows your engine to start cooling quicker. If you're not under load, chances are the 'stat will open and close, regulating temperature to a degree you never exceed 190*.. If you ARE under load, such as climbing a steep and sustained grade, towing, or hauling, your 'stat (no matter which one) will be wide open and the rest of your cooling system will be responsible for your operating temperature..

A 'tuned' engine running a 180* 'stat will allow the advancing of timing ONLY when the operating temperature hovers in the sweet spot of 175*~190* or so.. If you're pushing/pulling/hauling, or running the purple crap out of your truck, the PCM is going to sniff the operating temperature via temperature probe, the a/f via o2 sensor, and the air intake temperature via IAT, and adjust timing and a+f ratio accordingly.. In other words, toss the tune and the benefit of a 180* out the window..


Adverse reactions to using a 180* thermostat:

without rehashing the above, look for cooler heat from your vents... 'round about 15* cooler, if you can kinnit. The coolant that charges your heater core is cooler, and therefor you get less heat out of it... Us southern fellers don't mind that a lick, but you yanks may not appreciate that too much..


Is it worth it?

with a tune? yes...
without a tune? no...


long term effects:

hard parts and pieces in your engine are designed to live in a certain temperature range. There is some debate that the cooler 'stat never allows those parts to operate in the environment for which they were designed.. The (insert fancy metallurgical word here) coating on hard parts will fail over time.. but, we're talking a LOT of time..

Inspections and emissions:

with a tune: no worries.
without a tune: you is gonna fail, yo.. too rich.. ruh-roh..





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I think that is all.... Please add as you see fit, and we'll solicit HeyYou to clean it up, take ownership, and add it to the FAQ..

Thanks.

 

kudos and well written. +1 on putting it into the vault

 

I say ban him, useful info is not welcome.

 

D00d! Da fuel no splode! It jes burny-burny. When it splodes it makes knocky-knocky sound, is bad wrong.

 

Nice write up man!

 

I kinnit... Butz, me and an instructor in demolitions course argued this once.. my figuring is 'ifn it burnin fast nuff, it is jus splodin slower'... That's all tnt does, is burns really fast, displacing air 'round it and such.... Composition burns faster and hotter, but doesn't displace as much volume, so we use it for cuttin instead of pushin..

But, you is right.. it burns, it doesn't splode...

 

HAHAHA, DF is great, you guys rule. I think you need to "splain that a little more Ricky"

 

I was kinda sorta mostly just yankin' yer chain, but also gently dispelling the commonly accepted myth that the fuel/air mixture is exploding rather than just burning. And on second thought, the dividing line between burning rapidly and exploding is really dependent upon who's drawing it. Most folks go for the exothermic/supersonic rate of expansion definition, others contend that that's too rigid and doesn't account for enough of those cases that look all splodey but don't fit that definition.

So I'm'a STFU now.

 

Great write up! And another +1 for making a sticky!

 

if the pcm is in closeloop isnt it trying to get a lean 14.7 air ratio?if it is how can it be running rich if it is trying to get a lean 14.7?how fast will pcm go in to closedloop?2 5 10 minutes on a cold start up?obd2 far as i know pcm will try to get a lean not rich 14.7 ratio no matter the temp when in closedloop?only con i could see is the heater may not keep you warm.pros is less chance of ping,cool intake air charge,less chance of oil sludge,transmission stays cooler,less chance of the heads cracking,cooler engine bay.heat kills.180 in mine last sniffer inspection test past with no problem and was not run rich.