[COLVERT]

Originally Posted by SD1too

There are a couple of things puzzling me about this subject.

My SD1 had an oil pressure gauge. Whenever the coolant temperature climbed above 'normal' for any length of time, the oil pressure would visibly decrease. I always put this down to lower viscosity as rrobson has said. Wouldn't this suggest that there is a correlation between water and oil temperatures as Ian asked?

My SD1 didn't have an engine oil cooler but my 75 has. If the 75's coolant temperature rises wouldn't that mean that the heat exchange in the oil cooler would only take place at this higher temperature?

If my reasoning is correct then wouldn't the answer to Ian's question be 'yes'?

Simon

Well, there has to be a correlation as it's all happening in the same block of metal.--Unavoidable.

When these multi-grade oils first came out they had the name--Visco-Static--However that wasn't exactly true. The oil did thin when hot but to a much lesser amount to standard oils.

I don't really agree with the post above yours.


The bulk of the heat in the oil of an engine when it's running comes from absorbtion of heat from the block. Bearings generate a little heat but nothing like the amount coming from the cooling system. It would not take much to melt the white metal of the big ends and main bearings for instance.

As engine temperatures are limited to around the point of boiling water then that is the main governing facture of the oil temperature.

A good quality oil will have no difficulty doing its job at that heat. Synthetic oils are even better

Unless an engine boils dry there will be no breakdown of the oils molecular bonding.---

The point where the oil picks up the greatest amount of heat is from the jet of oil which cools the underside of the pistons and which lubricates the bores.