water tempreture and oil tempreture
 

when working an engine hard such as climbing a hill towing a caravan,
is there any correlation to oil temperature if I look at the water temperature gauge? I know it does not measure the oil but am I right in thinking that there is a relevance?

if my water is at the correct level and the gauge is showing hot (past 9 o'clock) then will my oil also be heading towards being "hot"?

macafee2

Depends which part of the engine the oil is in, quality of oil before it begins to break down etc.

For instance oil at the main bearings is likely to be much hotter than in the block next to a coolant jacket and under higher pressure too.

From experience the coolant will always boil and cause an alert before the oil degrades even with its raised boiling point due to being pressurised and containing antifreeze.

If the cooling system isn't doing the job it's supposed to be doing and exchanging heat away from the engine then yes, your oil will be heading towards hot, this is why oil coolers are fitted to most engines.

You'll boil the water off before you boil the oil.

Normally the oil will be running at a slightly lower temperature than the water.

thank you. I ask as there was a question posted on an other forum about oil temperature and I thought keep an eye on the coolant temperature but did not want to reply and look silly.

macafee2

No, there isn’t. The oil temperature can happily spiral out of control while the engine and water temp remains low. Without an oil temp sensor you’ll not know either. The rad and fan will do a good job of keeping the water something like therefore keeping the engine cool. But without a substantial oil cooler it can be difficult to control oil temp once it begins climbing. All that will happen is you’ll lose oil viscosity and wave goodbye to your bearings. Oil pressure is as good an indication as temperature but again without a gauge you can’t monitor it.

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.