oil temperatures

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May 30, 2002
Has anybody ever checked the oil temperatures in the same engine using different weights of oils? Such as a 5w-30 vs. straight 30? Or 15w-40 vs. 40? Or 30w vs. 40w? I have read that a "lighter" oil cools the oil better. Is this true.
I myself have not seen any proof to this concerning viscosity and temp differences, but i have seen this with boundary lubricants and how they make a difference in heat. Now there is a lot of theory to this and when it comes to reality, that is a different story when it comes to engines and different viscosity variations with heat, as there is too many other variables that actually come into effect other than just viscosity changes.
If the oil is too heavy it may cause an increase in drag on the system (kinda like pulling a load) which will in turn, result in more work for the cooling system....
So even in hot weather, you should use the lightest oil possible to have the best cooling, providing you have proper oil pressures?
BobIs, I think was is being asked is whether the Bulk oil temperature will change with viscosity. I say yes, that with high viscosities (50W or 60W), your are putting more HP into pumping thick oil (viscosity friction) and you can actually see higher temps on instrumented engines. So, yes, the lowest viscosity fluid you can use the better, assuming it has sufficient hydrodynamic and boundary lubricant properties. Bob, Do you have proof that the bulk oil temp is lowered with Moly or ZDDP? I say the only way you could really tell is to instrument the engine with thermocouples on the actual parts you suspect as having boundary friction regimes.
The last sentence should have read: I say the only way you could really tell if boundary friction additives lower temps is to instrument the engine with thermocouples on the actual parts you suspect as having boundary friction regimes. Otherwise, the bulk oil temperatures should vary slightly with viscosity.
Would i notice a difference in a change from 30w to 40w? Or even better, change from 30w to 20w-50?
Probably a better question to ask is whether the thicker oils have a higher or lower heat capacity than the thinner oils do. The higher the heat capacity the fluid has, the more heat it can absorb (and consequently release after carrying the heat out of the engine). (You need a good oil cooler to then transfer that heat out as well, otherwise it is mainly just moving it away from the hotspots and around the rest of the engine). If an oil had a low heat capacity it would flow right over a hot surface and not pick up much heat (and not increase much in temp either), leaving the bulk of the job to the cooling system. Antifreeze systems require a 50/50 mix of water because the water has the higher heat capacity of the two fluids, the water is doing the bulk of the heat transfer there. The higher viscosity oil will have the higher viscosity at the engine operating temp regardless,which is the point of using a higher viscosity oil in the first place...if your priority is on metal protection. There is more fluid friction internal to a higher viscosity oil than there is to a lower viscosity oil, but this should not be confused with the surface friction that is the focus of the METAL PROTECTION question. [ June 25, 2002, 07:03 AM: Message edited by: ZR2RANDO ]
Howdy MOLEKULE, any relation to the Electron brothers? he he, just had to do it! I read that too. Higher viscosity dictates higher film strengths, part of the definition. If you find info on heat capacity let us hear it, but remember it doesn't help much unless you give it a way to be dissipated, like a good oil cooler. Mainly the oil is just moving heat away from hotspots and taking it to cooler places so the water jacket can then take that heat out to the radiator,,but every bit helps and any extra heat capacity would be a good thing...and would raise the oil temp depending on where it was measured. see ya Ever met the ION sisters? he he
ION sisters [Confused] No, but while in St. Louis, I met this sweet polar-molecule (a German Girl from Iowa- a nurse) and ionic affinity resulted in two elemental species (kids) and a tertiary compound (grandchild). [Happy] Whew, Bob needs an instant Graemlin with a little shovel!!! [Cheers!]
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