Oil Coking in Tropical Climates

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JBT

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Should I be worried about oil coking in turbochargers in tropical areas like here in the Philippines?

From what I understand, coking in turbos happens when a hot engine is suddenly shut down (after a hard run) and the oil might coke because it quickly cools down. Temperatures here don't go below 25C during the day so the oil most probably will not suddenly cool down.
 
The oil coking is partly because the turbo is still very hot if shut down too soon after a hard run. The oil stops circulating at shutdown, and gets cooked in the hot turbo. A minute or so at idle after a hard run will avoid that. Synthetics with a good heat tolerance help as well.
 
Also kinda depends on whether the turbo is solely oil-cooled or if it's both oil and water cooled.

If it's oil cooled only, let it idle for minute before shutting it down.

If it's oil and water cooled, meh. Just don't do a quarter mile run and shut it down afterwards.
 
Thanks for clarifying my wrong understanding of coking. I'm currently using dino oil (Mobil Delvac 15W40) so I guess I'd better be more conscious of cool downs after hard runs.
 
Ideally, you would have a pyrometer installed (preturbo, i.e. in the exhaust manifold just before the turbo itself) and you would shut down after the temp is at 250F or below and the turbo has spun down.
 
If the turbo temp is 900*f no syn oil will stand up to that heat. It has to do with the turbo temps not the climates temps.
 
Originally Posted By: Jim Allen
Ideally, you would have a pyrometer installed (preturbo, i.e. in the exhaust manifold just before the turbo itself) and you would shut down after the temp is at 250F or below and the turbo has spun down.


The temp will never be at 250F in the exhaust stream. Turbo's spin down instantly (matter of a few secs). The exhaust is going to be well over 1000F when under load. You should let it idle and cool a bit but it will never reach 250F.

While pyrometer is a good idea it isn't needed, you just have to use common sense. Never shut down immediately after a high load like climbing a hill or freeway speeds. Let it idle for a minute and then shut down.
 
Hi,
Steve_S - You said this:
"It has to do with the turbo temps not the climates temps."

This is correct - the oil temperature leaving a turbocharger can be very high and well in excess of 120C (250F)

HDEOs and some modern PCMOs including synthetic lubricants handle this type of application very well

Most coking was/is caused by using an incorrect specced lubricant - use a recommended lubricant and especially in the correct viscosity for your application

A brief idle down period to stabilise the oil out flow temperature is well founded - a pyrometer is a great tool in this regard but is not needed - common sense is!
 
Originally Posted By: Thermo1223

The temp will never be at 250F in the exhaust stream. Turbo's spin down instantly (matter of a few secs). The exhaust is going to be well over 1000F when under load. You should let it idle and cool a bit but it will never reach 250F.

While pyrometer is a good idea it isn't needed, you just have to use common sense. Never shut down immediately after a high load like climbing a hill or freeway speeds. Let it idle for a minute and then shut down.


I beg to differ. They absolutely will cool to 250... or less. I've owned three diesel trucks and all of them were nearly the same in that regard, as were some I didn't own. If I start my truck and let it idle from cold, seldom will the exhaust temp even reach 150F, let alone 250F. This is the case for a truck I've owned for a quarter century, almost. The hotter they are, the longer it takes to cool down. I found that, while towing, a good coast-down run down an off ramp was enough to bring it down to 350 or so (from 6-700F) and a short idle brought it down to around 250F and I would then shut down. Even my gas truck will cool to that temp (yes, I have a pyro on it for tuning purposes).

As to spinning down, I don't really know how long it takes the average turbo to spin down, but I checked mine and it took between 30 seconds and a minute to stop spinning when shut down. Before writing this, I did a quick web search and note many people report largely the same thing, with 20 seconds being the lowest one I found (on a Bimmer gas turbo car). I know that in diesels, they can spin from 120,000 to 140,000 rpm at max boost and imagine it takes a while to spin down from that! I have several Garrett and RotoMaster turbo manuals that lead one to believe they spin at a fairly high rate of speed, even at idle and they caution that if you shut the engine off turbo off when, a) the turbo is spinning at high speed, it loses all its cooling and lubrication and at a high speed, with no lube, that's a lot of wear happening, and b) when it's too hot, it loses it's cooling and lubrication but that when the constant flow of oil stops, the heat carried in the turbo housing will instantly reach a very high temp. According tot eh Garret book, the oil temp in the center (bearing) section of the turbo runs at 180-250F... pretty close to oil temp. If you shut down when the turbine housing it at 350, for example, you can get an almost instant 100 plus degree rise and that's one way the coke is formed... massively, instantly oxidized oil.
 
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Apon further reading myself, you are correct.

I have never witnessed personally myself the turbo cooling below 300F but I guess if you want to sit there and let it idle excessively it would.

Then again it was gas engines, with turbo's not diesel and since diesel does run cooler at idle I can see how it would.

As far as spinning down, I meant more so from full load. IE don't fly into a parking spot building boost and shut off right away. If the turbo returns to idle speed and is shut off there should be no wear from that. It is a no load/free wheel spin down. Now there are turbo's with ball bearing shafts that take a very long time to spin down at shut off but again it is a no load condition. The ball bearings provide the support necessary to spin down without an issue.
 
Well, your comment got me to reading some interesting stuff as I made my "case" so thanks for the opportunity.

RE exhaust temp; it's been interesting comparing my gas truck's EGT vs the diesel. The gasser regularly runs at EGT that my diesel can only achieve on a long run at max boost.... one degree short of meltdown.
 
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