Re: Turbo cool down

Posted by NC Wayne on March 22, 2006 at 22:45:41 from (64.12.116.74):

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

Ok guys, wether you agree with me or not thanks for the replys. Now let me ask you this. Have any of you ever replaced a turbo due to a "heat related" failure on a stock engine? In other words have you ever melted a turbo down on a pure stock engine? Personally I've never seen or heard of it and I've been in the business for nearly 20 years and thinking bakc on my childhood to when dad was working on equiupment for the dealerships in the late 60's and early 70's I never remember hearing him tell of one either. True high heat and poor quality oil is a bad combination for the turbo's bearings/bushings, but if you use a quality oil that's not gonna be an issue either.--- One post begins by saying that he has the fuel turned up something like 17% and then says I'm wrong. Did I not say that turning the fuel up would cause excessive heat?--- Another post says turbos commonly run far in excess of the 25,000 RPM example I used. Did I not say I knew speeds were higher but was using 10,000 and 25,000 simply as round figures?---Several posts say that you need to let the turbo slow down or they'd sieze or get excessive wear. Did I not say that too? Was it not the main gist of my post?---One post says that a turbo only takes 10 seconds to spool down. Take the intake off and watch for yourself. See how long it takes for it to stop when you shut the engine down. I guarantee you it'll be more than 10 seconds. I've got a $50 for you if it slows down and stops in 10 seconds or less unless it's dragging or siezes---Another says that a turbo builds no boost until it's needed. Well, a turbo spins all the time and is always building boost, unless you have one of the new fangled ones with variable pitch vanes, etc which can control the boost almost infinately. One way I've seen and read about is by varying the angle the exhaust hits the impeller wheel. Sorta like blowing straight on a pinwheel or off to the side. In a normal turbo though what happens is as engine speed increases, turbo speed increases and therefore boost increases. If you don't have a waste gate that boost will continue to increase as engine speed does til it's doing all it can do at that particular RPM. If it has a waste gate it senses the pressure in the intake and either closes the wastegate to send exhaust through the impeller and increase boost pressure or opens it to bypass exhaust around the impeller and decrease boost pressure. All this to give a max boost pressure based on the factory preset of the spring pressure in the gate actuator.---As for oil to the turbo after shutdown, many mfgs have tried over the years to keep oil supplied with varying degrees of success using everything from stand pipes, check valves, acumulators, etc. I haven't seen any engines in recent years that have anything even remotely resembling a turbo post lube device. If you know of anything please let me know as I have searched the inernet, called mfgs, etc and haven't had any luck finding anything or anyone that knows anything about one. The only thing I found was called the "Turbo Saviour" which I've was told had wasted more turbos because of the design than it's saved. The best rememdy for oil related wear problems is a good quality oil and plenty of spool down time. ---Many posts also say that the exhaust temps climb higher when pulling hard and use their farm tractor, big trucks, etc for examples. Maybe I wasn't being clear, I was talking about your typical pickup, tractor, etc being pulled into the drive or barn at the end of the day. Not your tractor out in the field with an implement buried in the ground being pulled for half a mile at wide open throttle or your truck with a max combined load of 40,000 lbs pulling up a mountain. Then again many equipment engines are typically "turned up" higher at the factory for or by the owner than a normal vehicle engine anyway so they are gonna run with higher exhaust temps.---As far as my temps, I've taken them on a good cross section of construction equipment on the old two stroke Detroits (blown not turboed, but it's still a pressure boosting device), CATs, Cummins', Komatsu's, etc, All factory spec engines pulling whatever. The highest temps I've ever seen have been in the 700 to 800 degree range and that's typically on a 90+ degee summer day, with a load. Too these units were are typically in enclosures on a slow moving or stationary machine, both factors which limit the air flow around the exhaust. I had a turbo on one customers machine which was putting so much radiant heat into the air around it that it was causing false readings in the water temp shutdown switch 6 inches away and shutting the engine down. Even then temsp on it weren't much over 700 degrees. That's the main reason I started doing temps checks on different turbos so see what the normal temps were. That's also when I started looking into insulating covers for the turbo hot housings.---- I don't dispute the higher temps on up into the 1000+ degree range. I've heard about them many times over the years, he'' I've seen the stacks on pulling tractors glowing so I know their at least that hot. Still when I have heard of or seen temps that high it's always on an engine that has been turned up way beyond the factory specs or has been under an extreem load for a long period of time.....Bascally what I'm saying is I don't dispute any of ya'lls replys. There are all kinds of equipment out there and the minute you think you've seen everything something new comes around. Still I know what I've seen and done for over 20 years on my own equipment as well as customers equipment and I've never heard of needing to let the turbo "cool down" before shutting the engine down on a "normal" application with a factory tuned engine. My customer with the compressor engines that shut down from 1250 hasn't had to replace a turbo in nearly 2 years, (knock on wood), since I got him started using a really good quality engine oil. These units get started and stopped numerous times during the day and in operation have two speeds, 1250 and 2600 and there's nowhere in between. Depending on how many holes they drill, how many times they turn the air on and off as to how many times it goes from 'idle' to wide open in a day. Now your talking about an extreem environment... These turbos never get "cool down" time, just about 2 minutes of spool down time before shutdown for what good it really does since they still ru nearly 5 minutes after the engine stops. Even so I've never replaced one due to a melted impeller, cracked/melted hot housing, etc. In other words even under the extreem conditions they run under they have never suffered a "heat related" failure. Failure was always because of bearing/bushing wear due to the idle/shutdown speed and the resulting dry running time due to lack of engine oil pressure. Like I said a good oil has doubled the life of these turbos already, and the last time I checked the impeller play still felt good so they're well on their way to a third year, to me that says it all.......

Replies:

• Re: Turbo cool down Can't even use my name 14:11:11 03/24/06 (0)
• Re: Turbo cool down RodInNS 15:04:37 03/23/06 (2)
  • Re: Turbo cool down NC Wayne 19:20:38 03/23/06 (1)
    • Re: Turbo cool down RodInNS 20:04:54 03/23/06 (0)
• Re: Turbo cool down Burnie 02:30:32 03/23/06 (0)

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