Effect of t-stat on OCI/OLM

[NMBurb02]

Would switching to a lower temperature coolant thermostat (say from a 192F stock unit to a 180F "alternate temperature" unit) have enough of an impact on motor oil temperatures under normal use to affect the optimal OCI, as identified through UOAs or following an intelligent OLM?

The OM for my GP says that the OLM calculations are "based on engine revolutions and engine temperature", but I do not know if that temperature is coolant or oil. So if the engine stays cooler with a lower temp t-stat, would that keep the oil from reaching its optimal temp and therefore necessitate a reduced OCI? I wouldn't expect a 12F cooler t-stat to have much of an effect in a warmer climate like mine, but what about during the winter in colder climates (where people sometimes block portions of their radiators) or if dropping 32F from a 192F unit to 160F?

I am thinking of going with a 180F unit in the GP as it runs a bit warm for my liking and would never go with 160F unless I was tracking the car (which I will probably never do), and plan on following the OLM, so this is more out of curiosity than a need for adjusting my OCI.

 

[71Chevyguy]

Not sure how much it would affect the OCI because that also depends on your driving style. You can easily warm up the oil more by running it hard to get temps up. I will say that you may get a CEL because things are just not up to the expected operating temperature as well as having tranny lockup problems because temps are just not up to par. Not sure if 180 would do it in a warm climate like yours but a 160 would more than likely give you a CEL pretty quick. That is why most low temp thermostats are usually put in with a tune to make adjustments for "expected" temps in the ECU programming.

 

[Drew99GT]

I played around with thermostats on various GMs and I found that during winter conditions, 180 isn't optimal as engine parameters are set for 195, and during summer months, a 180 is useless unless you're at sustained highway speeds, because the radiator fans are set to turn on around 215 degrees.

If you're concerned about the engine running in the 215 to 230 range like many GMs will run in stop and go, you can either get the PCM reprogrammed to turn the fans on earlier or get a manual fan switch. If you go with the 180 thermostat, the engine temperature will still get up into the 200+ range until the fans turn on when in normal stop and go driving.

 

[SteveSRT8]

GM's OLM looks at coolant temp. Full warm up is essential for long engine life.

Without reprogramming a tstat does little as Drew noted.

Ford published a whole rack of data in HP books way back in the 60's that showed cylinder wear went DOWN when temps went UP.

But who knows if that is even applicable to today's engines...

 

[2oldtommy]

Running a lower temp thermostat can cause the emmisions to increase. As you are in CA, it could cause a fail emissions test.FWIW

Oldtommy

 

[loyd]

Lower temperature thermostats can have far-reaching consequences on several things. Cylinder wall washdown, poorer mileage, higher emissions. I'm sure there are other I've missed but I think you can see it's probably not a good idea.

 

[SteveSRT8]

Originally Posted By: loyd
Lower temperature thermostats can have far-reaching consequences on several things. Cylinder wall washdown, poorer mileage, higher emissions. I'm sure there are other I've missed but I think you can see it's probably not a good idea.


"Can" have but not "have to" is a very important distinction. Due to incredible variation among platforms there are some cars that respond well to minor tweaks and others that simply cannot (or should not) be modified...