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Thread Title:

Detroit Overheating


Created On Monday August 19, 2002 15:29 Diesel Talk
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firetech
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Joined: Aug 2002

Note Monday August 19, 2002 15:29 View thread in raw text format
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I have two 8V92TA that overheat, two identical trucks, these units are are fire trucks. I've evrything I can think of and have come to the conclusion that I have an air flow problem. The problem has been going on, off & on, since the trucks were new. Local detroit dealer can't find any problem and the manufacturer of the truck can't seem to find solution. So I'm kinda on my own. I've hads the rad. and heat exchanger checked, ok. The units do fine while idling, but while starting from a standing start and as long as the power is being applied the temp rises. When a cruising speed is obtained temp settles. At a speed of 45 or 50 the temp is ok, if speed increses temp increses. At about 55 or 60 the temp will climb to approx. 210 - 230 degree.

Thanks for your help.

Mike Henricks, Lubbock Fire Dept.
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thunderroaddrayage
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Posts: 14
Joined: Sep 2002

Note Monday September 02, 2002 10:54 View thread in raw text format
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Fire truck rated engines usually have fuel curves that are almost identicle to marine engines.The problem is that fire trucks must rely on a conventional truck type cooling system versus a marine engines extra cooling.The thinking is that these engines need maximum power for short periods of time and that they wont see high overall hours betwwen rebuilds.All diesel engine manufactures,not just detroit,sacrifice some lifespan to increase availible power.To put it simply,these engines are factory hot rods.I've seen people try to build truck engines up to these specs,with mixed results.Power is excellent,But because of injecter size and timing specs the overall lifespan of the engine is short by truck standards.Usualy 200 to 250 thousand miles before oil consumption becomes excesive due to piston ring breakage.While this is almost half the normal life span of a highway truck engine and is unacceptable with todays economics in the trucking industrey,200,000 miles is a very long service span for a fire truck.Since you didnt mention any R.P.M.'s at the M.P.H.'s you indicated,I'll have to go on assumption,which I hate to do.You say youve checked youre foundation cooling(radiator,water pump,ect.)and everything checks fine.I,d have to agree with this since you say temps are fine at an idle and more importantly at cruising speed.I assume cruise is at part throttle.I'll also assume that temp is fine at high idle P.T.O. speeds (pumping water,ect.).I'll assume that at 55-60 M.P.H. youre at full throttle,same as when youre accelerating.This would mean youre heat problem is only during high demand(full throttle) situations.When you take youre foot off the throttle,the heat drops.If I am correct in all my assumptions,then the reason youre detroit dealer cant find a problem is because you dont have a problem.What youre seeing as a problem is perfectly normal for this type of engine.Youre looking at airflow as the last possible cause.Although you might be able to cool things down some with electric fans like the hot rodders use on their cars,triggered by a sending unit or manually by toggle switch,you are looking in the wrong place.Youre intermittant heat is directly linked to youre right foot.If you were to run youre build codes,or just closely inspect the valve cover decal,you would find youre injectors are much larger than anything used in a highway engine,and youre timing is quite advanced compared to a highway engine.Heavy fuel loads and advanced timing can both cause excessive heat under high throttle,but combined, they always will.With a marine cooling system it is absorbed and goes unnoticed,but with a fire trucks conventional cooling system,the heat rise at full throttle is dramatic.Detroit two strokes are very high demand when it comes to intake air.You cant have too big of an air filter on a two stroke.Air inlet restriction can cause tempurature problems on two strokes,but it is usualy all across the R.P.M. range and will show a loss of power and fuel mileage proportional to the temp. increase.I would say youre problem comes down to "you cant eat youre cake and have it too".High horsepower makes high heat.If the cooling system is over powered,youre going to see it on the gauge.Since youre only seeing this at full throttle,I would ask the manufactures(truck and engine)if it was going to affect the warranty.If they say they will stand behind it,then run it and dont let it worry you.Its doing just what its supposed to.The fact that this is happening in two identicle trucks with two identicle engines would seem to reinforce the things Ive tried to explain.I hope some or all of this helps you and others.
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badges65
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Joined: Jul 2002

Note Wednesday September 04, 2002 00:33 View thread in raw text format
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HI,
just a 2 cents worth,
you could try installing a decent sized fuel cooler in behind the radiator take fuel from after the pump and return inbetween the primary and secondary filters.
don

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http://invertedvboats.741.com/
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Ron
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Joined: Jan 2003

Note Friday January 24, 2003 02:34 View thread in raw text format
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Just a thought....you have checked the engine coolant temperature with another gauge ? It is possible for the dash gauge to be giving a reading that is several degrees off.
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