Thermostats in Racing

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May 27, 2002
I took my laser pyrometer to the track this morning where I had sponsored a car. This is a dirt track about 6 km long, lots of 5 kph curves, and a couple of straight-a-ways, 10 laps per race. As each car came in I checked temperatures of various components on the cars (mostly 1600 to 2000 cc Toyotas, a Subaru, a couple of Nissans. The question is: Everyone was running without a thermostat, looking for the most possible cooling, yet none had actual temperature gauges…. Just the range gauge. Most water temperatures coming out of the block were running in the 77 to 80 C range at the end of the victory lap, while oil temperatures at the filter were running between 107 and 110. (Exception being one where the water was 110 and the oil 155 C, but the radiator was blocked with mud). The questions are: 1. Wouldn’t it be better to run with the thermostat and keep the water temperature closer to the 90 C range? 2. With a 30 C difference between water and oil temperatures, isn’t there a risk of cracking or other internal damage? 3. One car had an oil cooler installed with an adapter plate that I assume filters the oil before sending it to the cooler, then receives the cooled oil to mix back with the rest of the oil. From the size of the tubing it couldn’t have been cooling more than about 10%. Oil at the filter was 110 C like the others, but 75 C coming out of the cooler. Are all coolers only partial flow, or who can offer a better setup.
Full flow oil coolers are available. Oil coolers can also be install with oil thermostats to bypass the cooler during engine warm up. Use your favorite internet search engine and search for: spin-on adapters, oil cooler kit, thermostat, mocal, permacool...... I vote for keeping the thermostat or a flow restrictor(gutted thermostat). 'Rumour' is that fast coolant flow doesn't give coolant enough time to absorb engine heat. Flipside is that water pump manufacturers make higher flow water pumps that improve cooling even though normal thermostats can be used. This kinda conflicts with the above rumour. So, its up to you to experiment with your application if the thermostat, restrictor, or nothing works best.
There's no truth to water moving too fast to pick up heat--it just moves too fast to show much temperature rise. If the fast movement creates turbulence that results in air pockets, that's a different problem. No problem with the difference between water and oil temperatures--there are few places where they're both in contact with the engine metal, and you'd need to know the temperatures at those places. Check one of your truck or industrial diesel engines operating under a good load on a hot day...the oil will be hotter than the coolant, and the oil is probably cooled by the cool coolant coming from the radiator. Agreed, holding the water temperature constant would be a good idea, although 80°C might be good. There are sandwich type adapters that divert the full flow of oil to a cooler which mount on the filter assembly, if the cooler and hoses are adequate size. These adapters contain a bypass valve to ensure oil flow in case of restriction in the cooler, and at least one brand, Hayden, includes a 70°C thermostatic bypass valve in the adapter. I'd like to see the oil lower than 110°C. Ken
Undummy you hit the nail on the head. We used to use a plate of stainless steel with a 3/8 inch hole drilled trough it. This allowed the water or alchol mixture to flow at the proper rate. If the water moves to fast very little heat transfer takes place. I am sure a guted thermostat would work fine as well.
Hi, My sons Nissan 180sx runs a digital readout on the water temp via a Apexi FC, this shows usually 77-80c. He does use a thermostat. He also has a full flow oil cooler with thermostat and remote mount full flow filter (oversize filter). The oil thermostat bypassed the cooler until the oil is up to normal temp and directs the oil through the filter. The water thermostat modulates the water flow so that the motor runs at a faily consistant temperature. Unless of course it is running hot in which case it will just stay open. It is also possible to get differrnt temperature rated thermostats. Without either thermostat, oil & water temps will take a long time to come up to normal temp. Ok in a racing situation, but not very good for street. BTW the oil pipe coming out of the front mounted cooler feels cool to touch. The cooler is not that large but certainly fairly efficient.
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