[slaptj]

I have a John Deere 318, M00318X368388, with an Onan B43G engine. 600+ hours on the meter. I bought it used and have used it for the last couple years mostly to cut grass. It has always seemed to run hot - you can feel heat coming off the engine while sitting on the seat. It uses a pint of oil around every 6-8 hours. Recently it seems like it is losing some power on some days but then runs fine other days. The exhaust also seems to be popping louder. It will also backfire after turning it off sometimes.

I keep the cooling fins and the belly screen clear.

I don't know if all the symptoms go together, but thought I'd list them just in case.

Thoughts on what the issue(s) might be?

 

[turboaudi80]

Check for intake leaks. The manifold is two pieces stuck together with RTV. They are notorious for leaking. Remove, split, clean, reseal and reinstall. Clean the carb and check the little freeze plug on the side to be sure that isn’t leaking either.

My manifold was cracked when I got the tractor so I had to replace it.

Last, there is a rubber “grommet” that goes around the oil filter to keep the air flowing through the tin and the fins. If you don’t have it get one.

If you need parts call Boomer. He is super knowledgeable and has all the Onan parts.

Sent from my iPhone using Tapatalk

 

[slaptj]

Some follow up... one day I was working on this issue and had a backfire out of the carburetor. That gave me something else to search on and a multiple places suggested a bad condenser. I was not aware I had the points and condenser until now, so that took some learning. I tried a different condenser with no improvement. This week I looked at the points and it looked like there was little to no gap between them. Went and got a feeler gauge and adjusted them to .016 or .017 and today it ran smooth with good power, and it didn’t seem to run hot (hood wasn’t hot to the touch like it has been). Sample size of one, but improvement over last week. Still will probably reseal the intake manifold once I get time to take it apart some more.

 

[RussKish]

I would also recommend pulling the engine and removing the oil pan. My 420 (Onan P220) had a thick build up of sludge after 25 years of use. Also a fuzz ball (dog/cotton, dandy lion) had built up on the oil pickup and it would restrict the oil from pickup. So not knowing what has been serviced I would put that on the list as well.:tango_face_glasses:

 

[antiqueetc]

Onans do require some maintenance that your's may never have had. Decarbon and valve adjustment every 500 hours. Boomer, mentioned earlier will have the needed gaskets and is an invaluable source of Onan info.

 

[mrbeef]

Boomer is a great knowledge base (felt like I should reinforce that's little more )

I agree with doing some preventative maintenance.... However, I would run it a few more times before I went full potato on taking the engine out etc. Not that I don't recommend doing the cleaning, decarbon etc, but if the engine now runs fine you have some time to plan maintenance and observe the engine to see if anything else might be needed. Same with restraint the intake manifold, if it's not broken no reason to split it and reseal. Done properly with new gaskets the reseal will take about 5 hrs and cost $30... Don't spend time and money doing that if you are going to decarbon in the near future.

 

[rwmeyer]

Run engine to warm up, then spray carb cleaner or starting fluid around intake manifold at head and along seam where 2 pieces come together. Any increase in engine rpm indicates you're sucking the cleaner or fluid into the manifold and you have a leak!

As far as possible overheating: Harbor Freight and others have infrared type temp tools...point at engine, read temp. About $25 and not dead accurate, but gives you an idea. I'd guesstimate 285ºF to 300ºF (max) would be about right. Bob