Oil Cooler Thermostats re

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davedpc

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Is anyone knowledgeable with these items on T.D engines. My understanding is they allow the oil temp. to reach a higher than normal temp. to prevent the bores from glazing especially on boats not regularly used under load. These high temps. result in very viscous oil which is prone to little leaks. One of my local dealers recomended quote 'put a hole in the diaphram' as my boat is normally used under heavy load. Dave.

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Thats a new one for me!, The reason for having a thermostat on the oil cooler is to maintain the oil at a viscosity suitable to support and provide lubrication for the bottom/main bearings of the crankshaft (and any other bearings in the engine), and to provide a certain degree of cooling/cleaning at the same time especially on the underside of the piston. if the oil is too hot, the viscosity drops thus reducing the thickness of the oil vedge formed under the bearing allowing possible contact under fireing forces. The piston rings will also struggle to glide up/down the bores if the vedge of oil formed under them becomes too thin leading to possible contact. Too cold and the oil becomes too thick to be passed through the fine clearances between the bearing/shell leading to overheating/scorring.
Glazzing of the bores is usually down to 3 types of wear, 1) abrasive carbonaceous particles from combustion process drag up and down the bore with the piston scorring the liner 2) corrosion of the bore from high sulfur fuels and moisture in the inlet air (not too common on engines using diesel) and 3) scuffing wear resulting from metal to metal contact usually caused by worn piston rings, blow-by, lack of lubrication, overloading of the engine.
In other words, it is very important to keep the oil between a certain temperature range (which is governed by your oil thermostat). This temperature range will vary with the type of oil that your using and the type of application.
My advise...... dont put a hole in the diaphragm and alloy the oil to increase in temperature as you will set yourself up for some potentially serious problems.
Its even possible if the engine is large enough to suffer a crankcase explosion.
hope this made sense.


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Err sounds like a complete load of rubbish to me too!

Any oil cooler thermostat CANNOT allow the oil to get hotter than the same cooler without a thermostat (apart from v minimal possible restriction in the flow). Surely the whole point of a thermostat is to allow the oil to warm up quickly by preventing permanent cooling - no ?

Again <<high temps. result in very viscous oil>> err no the hotter an oil is the thinner

Again <<which is prone to little leaks>> err no IF it WAS very viscous then it wouldn't leak

If the meaning was that the thermostat allowed the oil to warm up quicker thus being less viscous and lubricating better then this will reduce bore glazing on a newish engine. I've bored everyone on the board with my opinion on how glazing happens - light load running from cold, especially with a turbo'd engine, gives low compression pressures which doesn't press the rings against the bores and any initial unburnt diesel (which is a v good lubricant (it is the only lubricant in an inline injector block)) allows polishing/varnishing effect on the bore and then rings never settle in to a good gas-tight seal.

Not at all convinced <<a hole in the diaphram>> will do much good either way. What is much more important is to be sure that the thermostat does fully open. Most recently designed diesels and ?? all turbo +/- intercooled ones, use the oil to spray underneath the piston head and provide approx 30% of the total heat removal to prevent the engine siezing up - that's why diesel's oil gets so hot in comparison to a petrol motor and many/most diesels have an oil cooler whereas only better/tweaked petrols do. If not enough is getting through an open thermostat a little hole won't be much help but then again it won't make much difference to the warm up time of the oil from cold.

I think somebody has been spinning you a yarn or understands v little!

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Thank you the for the answers above . They make sence. The advice I was given was from a main Merc. dealer. Sorry about the stammer (3 posts) but the bloody machine just would not accept my post but just kept instucting me to continue. Why is this . Going by other posts it looks as though I am not alone.

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Tee hee hee NM

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Perhaops not so much rubbish - depending upon the design of the system and the operation of the engine.

Our hire fleet had endless problems with Perkins 4-10x engines turning their oil to "grease". At the time Perkins insisted the engines be fitted with an oil cooler.

The only thing different between the Perkins and our Volvo, Lister,,and BMC engines was that none of them oil coolers. Disconnecting the oil coolers imidiately stopped the problem.

In my view, the low power river use with constant stops for locks prevented the oil reacing 100C, so they never boiled the condensation out of the oil.

IF the oil cooler in question was a bypass type (i.e. it cooled the oil vented by the PRV) OR the thermostat in question allowed the oil to bypass the cooler the stat would then alow the oil to reach the engines designed oil operating temperature and prevent the problem above. This onlyn applies to engines operating at low power.

In my view it would have a minimal effect on bore glazing because my research indicates its related to cylinder wall (and possibly piston wall) temperature in the combustion area.

Tony Brooks

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Re: Oil @ 100 degrees

Hello Tony
The problem with the oil turning to grease was more than likely due to a leaking oil cooler allowing water ingress into the oil. This will cause a nice emulsion in the sump which tends to look a bit like grease.
I've not yet seen or worked on an engine yet where the oil temperature is kept above 100 degree's (its usually around 70/80 degrees).
It starts to be difficult to design an oil with a correct viscosity for the engine at above 90 degrees, then keep within that specified viscosity range when the engine is starting up from cold.....this is called the 'viscosity index' of the oil and relates to what viscosity an oil will be at a certain temperature.
Simon

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Re: Agree 100%

Tony

You are exactly right, perhaps I misread what was meant by

<<allow the oil temp. to reach a higher than normal temp....... especially on boats not regularly used under load>>

if the "normal" temp on a lightly loaded engine is being kept below the normal normal usual temp of a loaded engine. But then he did say

<<These high temps. result .....>>

Your example of ? over-cooled engines was not what I thought he meant

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