Oil cooler thermostat

With the stock cooling system my 350 Vortec would get extremely heat soaked in traffic especially pulling a trailer at low speeds. Trans would get 250+ and engine oil temps closer to 300. A 34" radiator with the GM oil heat exhanger, an external trans cooler after the in-radiator heat exhanger and a duramax fan blade on a Trailblazer SS fan clutch stopped of that.

L31MaxExpress said:

With the stock cooling system my 350 Vortec would get extremely heat soaked in traffic especially pulling a trailer at low speeds. Trans would get 250+ and engine oil temps closer to 300. A 34" radiator with the GM oil heat exhanger, an external trans cooler after the in-radiator heat exhanger and a duramax fan blade on a Trailblazer SS fan clutch stopped of that.

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What were your coolant temps? My trans has never been to 250 degrees in my 1500. As soon as I do a cool down lap in the Camaro with no oil cooler, my oil drops 30-40 degrees by the time I get back to the pits (~2 min). I have no explanation for your oil temps as they defy logic. Oil tracks right in line with coolant until you zing the thing up, then it builds real heat which, in my experience, is quickly absorbed as soon as you let the RPMs back down.

alpinecrick said:

I'm listening, and it's interesting what you're saying. So you're experience the auxiliary cooler is sufficient to keep the oil at operating temps when driving slow or towing with the 5.7's. An engine oil and trans temp gauge pod is something I have been considering.

Also, a thermal bypass can keep the temps up in operating range in cold weather.

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To be clear, I never put an oil temp gauge in my trucks because, based on how it acts in the Camaro and Corvette, I deemed it unnecessary. Yes, a thermal bypass will keep oil warmer in the winter, but all the ones I've seen are 160 and 180. I wouldn't be surprised if the oil runs even cooler than that in the winter with that kind of setup.

Supercharged111 said:

To be clear, I never put an oil temp gauge in my trucks because, based on how it acts in the Camaro and Corvette, I deemed it unnecessary. Yes, a thermal bypass will keep oil warmer in the winter, but all the ones I've seen are 160 and 180. I wouldn't be surprised if the oil runs even cooler than that in the winter with that kind of setup.

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So engine oil temps in the 200-250 degree range are what you consider optimum?

200-220 is what manufacturers consider optimum. 212 degrees is what the big number on your oil weight is rated at. For a 5W30, it's a 5W at 32* and a 30W at 212*. 250* is not enough to get me to increase cooling capacity. My Camaro has lived over 300 degrees since I got it in 2013, and it's been a race car since 2009. If the small cooler that I'm adding gets me down in the 250-270 range that'll make me more than happy. What you're forgetting is that hotter oil flows faster which helps it cool better. Obviously 300+ is not ideal, but it's far from an immediate death sentence. I'd get the gauges in then go from there. My 1500 does have a trans temp gauge and here in CO in the winter it barely gets over 100 with stock radiator and aux coolers. In the summer, it's 160-180 when towing. The key to keeping the trans cool is keeping the converter locked. If you're an off road guy, your best be may be an aux cooler that's not exposed to direct airflow but does have an aux fan with thermostatic switch.

What still has me curious is why the factory installs external oil coolers on trucks with tow packages if you believe those coolers would keep the oil below optimum range.

As you are probably aware, a thermal bypass gradually opens up and can act as a thermostat by allowing some fluid to circulate to the cooler(s), and some fluid to bypass back to the motor. I can see if in really cold weather theoretically a 180 degree bypass may not allow the oil to reach 200+ degrees. But I don't think that would usually be the case. I need to do some research and see if there are any 200 degree thermal bypass units out there.

I do a lot of work on the Front Range and make 10-15 trips a year across the mountain in my K1500's, and have numerous passes with sustained climbs with 2k to 4k ft altitude gain--the TQ is rarely locked up when climbing like that and is often down in third and sometimes 2nd gear. But most GMT400's pickups sold here in Colorado came with an excellent factory stacked plate trans cooler so I don't worry too much--but a trans temp gauge would definitely be more informative.

I have a 96 and 02 G1500 cargo vans and the 96 does NOT have the external cooler. It's everyday payload is maxed out plus I have a stack of ladders on top 2-3 ft high that act like a big sail--the TQ doesn't get the chance to lock up very often. The rebuilt 4L60E from a trusted builder is pushing 100k, but I keep the fluid BRIGHT red in all 5 of my 4L60E's (three hav been rebuilt) and have come to the conclusion that is the "trick" to long-lived 4L60's. All my trans pans now have drain plugs in them and I drain the oil out of the pan several times a year.

Back to engine oil coolers, I am indeed curious what a sustained climb with a load--trailer or full bed of gear/tools would do to engine oil temps. I don't know how accurate my factory water temp gauges are but my 96 K1500 has an after market radiator with the core 7/8" thicker than the factory radiator that came on it and according to the gauges seems to run a bit cooler than my 97 K1500 with the factory radiator--and the 97 has a 100k less miles than the 96.

If you're climbing a hill in 3rd, try pulling the shifter back to 3rd and the converter may lock depending on throttle position. I've been down I70 west through to UT and am familiar with the climbs. A tune would keep the TCC locked and the trans happy. I can say that earlier C4 Corvettes came with oil coolers and the switch to Mobil 1 synthetic factory fills marked the end of that. I'm pretty sure the engine oil coolers were TBI and diesel-isms. Having never put an oil temp gauge on either one, I couldn't tell you. I can say that increasing torque and altering the tune allows my truck to run 1 gear higher when loaded and for that my temps have been rock solid. Before I would consider adding an oil cooler, I would first validate the need with a gauge instead of relying on GMs aux oil cooler logic to dictate your decision.

I take your point about installing gauges first, they are on my short list anyway.

All the 2500/3500 GMT 400's I've looked at in Colorado had engine oil coolers on them, including the 5.7's.

So, I'll probably start a new thread, but what gauges and pillars do you like? Like the looks of the Autometer factory style gauges, but it appears the idjits don't make an oil temp gauge in that style.

Were they engine oil coolers or trans coolers? I just don't see that many at all when I'm in the junkyard. I like my Autometer trans temp gauge and do aspire some day to add oil/trans temp to the dually. I got some plastic dual gauge pod off of Summit made of plastic for my 1500, it goes on top of the stock piece and fit well. I used SEM grey interior paint from Napa and it matched halfway decent.

Supercharged111 said:

What were your coolant temps? My trans has never been to 250 degrees in my 1500. As soon as I do a cool down lap in the Camaro with no oil cooler, my oil drops 30-40 degrees by the time I get back to the pits (~2 min). I have no explanation for your oil temps as they defy logic. Oil tracks right in line with coolant until you zing the thing up, then it builds real heat which, in my experience, is quickly absorbed as soon as you let the RPMs back down.

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240-260 with the factory radiator and 5 blade fan. No cooling system problems either other than a massive condenser dumping heat from a dual evaporator setup in front of the radiator. Takes a powerful fan to expel the heat out of an Express van engine compartment. I got it down around 210-220 with the plastic vortec 9 blade job and a HD clutch. The Police Tahoe electric fans with the more powerful motors and more blades did not work for it. Overheated faster with the Tahoe fans on a 454/8.1 radiator than the factory clutch fan and radiator. That is when I backed up and punted the electrics. Trimmed the OEM shroud and installed the duramax blade. Its never run over 210F with the Duramax fan and that was at sustained WOT for 50+ miles. I am sure the 30-40 mph headwind while running 70 mph helped keep it cool though