I thought I could fix this problem, but now-----. I don't know. Yanmar YM2500, used, not reconditioned, 1070 hrs. starts and runs good, til it warms up. then, at idle speed, will experience intermittent bursts of speed for 4-7 seconds, up to 12-1500 rpm, then slow back down. this burst of speed is accompanied by rather distinct fuel knock, til it idles back down. runs fine at operating rpm, minor smoke, like a diesel should. also, burst of speed is also accompanied by white smoke!! Now, if that is not enough, I am losing small amount of coolant. could it be going into combustion chamber? would the coolant loss cause erratic pump operation,(bursts of speed)? I have drained all fuel, replaced filter, replaced rubber fuel lines, bled system, etc. all the easy things. God, I hate to have to tear into engine. I have owned tractor only a few weeks, and the guy before me was less than honest about known problems with tractor. any help would be appreciated. thx to all.
fuel knock at idle
- Thread starter tmar04
- Start date
SailorBob
Gold Member
tmar04 said:
Coolant leakage and white smoke sounds like a head gasket..(had that problem with my Yanmar).
DieselPower
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I would suggest getting a oil analysis done to check if you have a internal coolant leak. Even if you do I highly doubt it would cause the problem you describe unless it's dumping large quantities into the oil and causing the oil to turn into a milk shake. Odd idle characteristics can usually be traced to the fuel injection governor.
ctjstr
Silver Member
I'd be inclined to look at doing a compression test or even better, a leakdown test. The leakdown you can do with a standard tester, once you get the right size adaptor. The Compression test requires a tester specific to diesels. I just bought one for about 50 bucks. Not great quality, but will get the job done.
The smoke sure sounds like a head gasket, but I'd expect the problem to be more noticable at initial start up, rather then the other way around.
I've seen head gaskets cause eratic idle, but yours seems to be a lot.
Head gasket shouldn't be all that bad of a job.
I'd agree on doing an oil analysis though.
Have fun..you're about to become one with your tractor, grasshopper
The smoke sure sounds like a head gasket, but I'd expect the problem to be more noticable at initial start up, rather then the other way around.
I've seen head gaskets cause eratic idle, but yours seems to be a lot.
Head gasket shouldn't be all that bad of a job.
I'd agree on doing an oil analysis though.
Have fun..you're about to become one with your tractor, grasshopper
GinNB
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Inspect the block VERY carefully up as close as you can stick your nose. Use a magnifier if you can, and a flashlight if your light isn't as good as daylight. Try and see if the top of your block is warped. A known flat piece of glass will help if you can lay it flat on the block and look between it and the block for tiny gaps. An exhaust gas analysis on your coolant will tell you even if you've got a very small leak. Call your local rad shop and ask them if they can do it on coolant outside the engine (never seen it done but it might be worthwhile). Take them a sample if you have any left).
I don't remember much in the way of white smoke but I've had air in my injector lines after having to bleed the fuel system cause speedups until they got worked out. Didn't last too long though. Almost complete fuel blockages between the tank and injector pump can cause random speedups under low-load/low-rpm conditions as well, but fuel starvation will be evident when you try to run the tractor faster.
I don't remember much in the way of white smoke but I've had air in my injector lines after having to bleed the fuel system cause speedups until they got worked out. Didn't last too long though. Almost complete fuel blockages between the tank and injector pump can cause random speedups under low-load/low-rpm conditions as well, but fuel starvation will be evident when you try to run the tractor faster.