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Motor oil question

Will synthetic motor oil make my engine run cooler then regular 10/40 motor oil? I own a 1964 Pontiac GTO that runs around 200 degrees. I have heard that by using synthetic oil, the oil stays cooler and that also brings down the water temp.


It will run at the same temperature as with conventional oil.

What synthetic does do very well is to resist viscosity breakdown at high temperatures better than conventional oil. However, this is not because it causes your engine to run cooler. Instead, it is the difference in its chemical composition that allows it to resist viscosity breakdown at high temps and to flow more freely at very low temps.

Your “heat” problem, whatever it is, has very little relation to what oil is in the crankcase, unless it is extremely heavy oil which would heat up the bearings excessively.

If you are using 10W40 now, you should probably shift to 10W30 in the summer and 5W30 in the winter. The 10W40 grade is good for tropical countries where you always have hot weather.

Your cooling system is designed with a good safety margin; the THERMOSTAT, if it’s working properly, will regulate how warm the engine runs. If the engine generates more heat, it will just stay open longer.

Synthetic oil of the same viscosity performs the same as regular oil. It may start the car more easily at extremely low temperatures, and may stand up better when you are towing a trailer aross the Mojave desert in July.

Check your owner’s manual; 200 degrees may be the exact operating temperature your cooling system is designed for. Cars run more efficiently at that temperature than at 180 degrees.

Your GTO is a “hot” car, so operate it according to the owner’s manual. Synthetic oil is good oil, but it is also very slippery, and with the loose tolerances (clearances)of a 1964 car, you may end up “using oil” if you switch to synthetic.

P.S. My 1966 Chevelle Malibu with a 283 V8 had a 180 degree thermostat. I don’t know what your model GTO takes, but it’s worth checking. At 200F the engine runs more efficiently but the cooling system has to be carefully monitored. Modern cars all run much hotter than 180F.

CHECK your owner’s manual.

Synthetic oil will not make the engine run cooler.

What’s wrong with 200 degrees? If it stays there I’d say everything is fine.

The advantages of synthetic are best realized under high stress situation, like extended oil change intervals, low temp operating conditions etc. Under normal use and oil change intervals of 5K, there is little need to consider the added expense IMO, unless the manufacturer recommends it.

Acturally synthetic oil will run cooler, but the difference will be so small that you will not be able to measure it.

200 degrees is perfect.

Synthetic will withstand high temperature such as those produced by turbos better, but it will not dissipate heat better. And, you want the engine operating a full normal operating temp. You do not want it operating cooler. The engine’s designers have included a thermostat specifically for the purpose of allowing the engine to reach and maintain proper operating temp.

Cooler means more wear, reduced gas mileage, and (if cool enough) excess gas that could wash down the cylinders.

In short, you have a really cool car that’s running perfectly, ast least as far as the cooling system. Don’t fix it. It ain’t broke.

The operating temperature of your motor is regulated by the thermostat. If 200 degrees is too hot, put in a 190 or 180 thermostat. Higher temp usually means a bit better combustion and less pollutants so new cars run hotter than older “classic muscle cars” like your GTO.

Synthetic motor oil may have advantages over conventional oil. If synthetic oil means less friction that would be good. However, you won’t see a lower operating temperature due to the thermostat.

I recall several commercials for oils and additives that claim to cool the engine but see no possible way for that to be true. If an oil reduced friction, which reduced the temperature of the pistons, cylinders, etc., the thermostat would just pass less water to keep the temperature up. Some of the lies in infomercials should be outlawed. I have seen them drive half an hour with the bottom radiator hose cut off and them pull the drain plug out and continue to drive another half hour claiming that the special additive was protecting the engine. That’s as phony as Championship Wraslin. But it seems enough people buy into both of the lies.

Well, I mostly agree. One of the functions of motor oil is to wash a bit of heat from the cylinder walls. However, the heat comes from the cumbustion process rather than the friction. Perhaps friction contributes a tiny bit, but it isn’t that significant a contributor.

Having said that, I agree that it’s the T-stat and a decent cooling system that regulates the engine temperatures and not the oil.

Your comments about commercials are spot-on. I’l’ add CarFax to the phony scams bucket too. I really wish some agency would investigate the accuracy of their data. IMHO it’s fraudulant.

Championship Wraslin is fake?