Re: Turbo cool down

Posted by Billy NY on March 22, 2006 at 06:04:07 from (64.12.116.74):

In Reply to: Turbo cool down posted by NC Wayne on March 21, 2006 at 21:31:01:

With a slight understanding of the basic principles of a turbo, like I think I have,LOL ( I don't know the fine details), but know the bearings have an oil line to them and are lubed, as well as the temperatures in there, like on large truck engines. I used to drive for a living and as the air cleaner gets restricted the temperatures will rise, and I forget the max. shown on the pyrometer, 1600 ? but 1200 deg is hot, you are supposed to keep tabs on the temp., if it gets into a certain range you should be cleaning the air filter or changing it from what I recall and or downshifting, letting off the fuel. When you are lugging up a hill and at a lower r.p.m. but have the pedal down feeding it a lot of fuel, it seems when they get real hot, you can control this, by letting off the fuel or down shifting, r.p.m.s increase and the temperature goes down. Obviously that turbo is there to help when the motor starts to lug, at least that is my understanding of it, could be wrong !

I have an example to use, my place is atop a hill and I've got a small car with a turno on it, with a vacuum gauge, no pyrometer, if I really hit the fuel on the way up in a higher gear I can really get the needle to advance on the vacuum gauge, assuming if it had a pyrometer, it would show the dramatic increase in temperature while climbing the hill and the pedal to the floor, in a higher gear with plenty of r.p.m.s left before shifting, (even in this little mercury capri that turbo can be noticed, snappy little car actually) As soon as I get to the top and pull into the driveway, just a few seconds before, it was hot and working hard to do its job, I never just shut it off, on this one MFR. says to let it idle for at least 30 sec. I give it at least a minute, but the reasoning is for oil to keep circulating until it cools and stops spinning, for reasons mentioned above, if you shut it down you could seize a bearing, due to the heat and lack of lubrication, assuming that to be caused by the oil coking up as mentioned.

So in theory it's best not to shut an engine down after a hard acceleration or right after it's been under a heavy load, if I understand what I've learned from others on this and what I've read on different manufacturers warning stickers. This little car has 124,000 miles, orginal turbo still, knock on wood.

I remember how powerful some of the tractors I used to drive were with no trailer, many times I'd get locked out of the yard when coming in late and just drive the tractor home, really feel that turbo with no load to pull, they are amazing for what they do, sets you back right in the seat if you get on it.

Same was true for extreme cold starts, on the Mack's I remember we had a fuel shut off in the cab, used to crank the engine for a bit to get oil up to the turbo before giving it fuel in low winter temperatures, that was to allow the turbo to get some oil into the bearings, assuming the oil would flow, really not sure if this was helping it any, but a co-worker back then who used to run a few trucks coast to coast said he did it for this reason. Made some sense.

I have heard of turbos failing in some large Cat dozers while in a heavy push after the operators stalled them out and could not get them immediately started again, that makes sense, I have ran plenty of D8K's and when you are working hard they get real hot, used to heat my lunch on the exhaust manifold, it did not take long for a hot lunch to be ready. It's a good thing to learn and know about if you are running any engine with a turbo, lot easier to let it cool than replace.

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