Thicker oil make engine run hotter?

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May 25, 2005
This is a noob question, but does thicker oil actually make the engine run hotter? I have an 87 civic with the 1.5 w/220K miles (which calls for 10w-30)and have ran 10w-30, 10w-40, and 15w-40, and the temp gauge needle always sat at about the half mark. The day I changed the oil out to 2 qrts of Trop Artic 10w-30 synth blend, half a qrt of Mobil 1 10w-30 that I had laying around, and 1 qrt of SuperTech 20w-50 to help with some oil burning issues, I noticed the temp gauge needle sat at the 3/4s mark and thats where its been for the past 800 miles. Could it be because of the qrt of 20w-50?

thanks in advance
Just a shot in the dark but maybe the extra thicker oil adds more resistance which in turns causes alittle more heat. I could be wrong.
Although I don't think so, even if it did force more btu's to be sent out the rad ..I wouldn't expect to see it on the gauge. The oil temp may or may not vary a tad.

I'd look for issues in your cooling system.
Thicker oil will increase bearing and oil temperatures. I agree with Gary, it shouldn't have enough effect to change your coolant temp much . . . as long as your cooling system is working OK to begin with.

Looking at your current oil mix, I doubt it is any thicker than a -40 weight, which you have run without an issue. Check for a thermostat or radiator problem.
i agree that is way too much of a difference from the norm for it to be the oil. check out the cooling system.
I believe thicker oil is less efficient at transfering heat.
It heats up slower and cools slower than a thinner oil.

As oil is responsible for 40% of the engine cooling in a
water cooled engine, ( 60% in an air cooled engine)
so the answer is yes, a thicker oil will make for a
slightly hotter engine in the spots where water cooling
cannot get to.
I have demonstrated that oil viscocity can influence the oil temperatures on race track operating conditions. Any of 3 high quality synthetic 5W-40 oils operated a full 15dF lower than any of 3 high quality synthetic 15W-50 oil. In addition, the 5W-30 oil operated about 5dF higher thant he 5W-40 oils at the race track.

I suspect that the 20W-50 has a lot of VI improvers. These, when mixed with the relatively un VI improved xW-30 oils, ended up with a thicker oil both at startup and during normal operation. This thicker oil cause more energy to be absorbed by the oil-pumping process. At normal operating condition, however, I would expect only the smallest of change in the oil temperature. Since the guage indicates more than a little change, I suspect the 20W-50 has changed the brew in an unsueful maner.
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