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Discussion Starter · #1 ·
OK, so I'm an ATV Mechanic trying to repair a sled, that's the first problem.
While looking for an overheating problem I found combustion gasses entering the cooling system, causing air pocket, resulting in a high engine temp reading on acceleration (at idle the temp is fine). Thermostat tested OK, opening at 135 degrees.
After replacing the head gasket o-rings (yes, one o-ring was broken), I still seem to have the same symptoms.
I have torqued the head to 21 ft. lb's, and bled the cooling system.
Any suggestions would be helpful.

Thank's, Bob.
 

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Temp sensor/sending unit failing? As soon as you stop it says it's cool? Did you get all of the air out of the exchangers?
 

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Discussion Starter · #5 ·
I'm pretty sure I have all of the air out. I'll be back at it tomorrow. The temp sender appears to be correct, as it does cool off rather quickly after it returns to idle.
I ran out of time on Thursday to perform another combustion gas test, but I'm pretty sure that's what I'll find, head gasket leakage.

I guess that's why I'm inquiring if there's supposed to be a thin coat of high temp case sealer applied to the cylinder in the area of the head gasket/o-ring.


(Just in case anyone tried to click on my website and couldn't make it work, I fixed the address in my profile).
 

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You don't need any kind of sealer on the gaskets. Last thing to check, it's a b*tch...The water pump has a plastic impeller that wears down with age. Go to your year and model and click on engine, rotary valve and water pump. Part number 7 there.

Microfiche

That would be why it overheats at speed, the pump won't push it quick enough. Good luck.
 

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Discussion Starter · #7 ·
Nice try, but after removing the starter and water pump housing, the impeller looks brand new.

During the problem, I find that the upper hose is hot and the lower is cold, leading me to believe there is lack of coolant flow.

-Thermostat tested OK at 135 degrees

-Water pump impeller OK

Unless I still have combustion gasses causing an air pocket at the thermostat, causing it not to open.

All that is left is an obstruction in the cooling tubes or the radiators. I guess that's where I'm off to now.
 

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The impeller is turning OK? Did youpull it over with the cover off to be sure it's not stripped, etc? If there's air trapped in the exchangers it'll overheat also. I'm stumped...:confused:
 

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Discussion Starter · #9 ·
Yes, the impeller is turning with the engine, and does not appear to have stripped splines.
I flushed the radiators/heat exchangers and they seem to allow adequate coolant flow.

I just got back from driving it, and still no difference.

The heat exchangers are getting warm, as does the upper and lower hoses, so coolant is flowing through the system. But, there is a cooling system hose that runs verticle between the pressure cap housing and the lower hose "tee". Makes me wonder if the coolant is bypassing the heat exchangers through this hose. And, by having a small restriction in this hose, would divert more coolant though the exchangers.

It's jetted at 210 main (single carb) at 6000 feet. Although the plugs are a good color, maybe I should try a 230. You wouldn't think that it should make that much difference. Stock main jet is 280, but that would be sea level.
 

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Discussion Starter · #10 ·
wyorider said:
And, by having a small restriction in this hose, would divert more coolant though the exchangers.
Just found the restriction. It's in the other hose, close to the pressure cap housing. I found it by squeezing all of the hoses.

Now, I wonder if it's not supposed to be there?. It's not on a parts fiche, but it may be put in a hose from the factory.
Can anyone verify having one of these in there upper hose.

Thank's, Bob
 

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Discussion Starter · #11 ·
And, just re-tested for combustion gasses, all OK (liquid indicator color stays blue). That still doesn't mean that it's not happening when accelerating, while it runs hot. But I have to rely on the test instrument.

Went up to a 230 main jet, and it lowered temp by about 20 degrees celcius. That puts it on the edge of the hot zone.

Too bad it loads up now at low RPM's. I'll try to adjust it out and still keep the 230 main.
 

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Discussion Starter · #13 ·
Went from a 35 to a 30 pilot, needle at 2nd (from the top), and one turn out on the screw.
Temp stays at about 80 celcius, and runs strong.

Looks like this thing is finally leaving my shop.

Thank's for the help smallengineguy. Hopefully someone else will get some benefit from this thread.

Bob
 
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