Cooling system help needed

[butcher bergs]

What would cause a condition where coolant would overfill the resevoir during times where increased engine heat is being produced?
The machine is completely fine under light to moderate operation however when plowing or being ridden spiritedly the coolant res spits out of its fill cap.

Recent radiator cap
Rebuilt water pump
All other mechanicals appear to be in good working order

Is there a chance the t-stat could cause this?

[jasnmar]

Compression leak?

In my experience with Thermostat failures they generally start by sticking at "random" times. Is it doing this consistently?

[stoinkythepig]

Sounds like a head gasket to me.

[Paul_E_D]

Classic head gasket symptoms. It will get gradually worse.

[butcher bergs]

Jason- Consistent results and as described above.

Exhaust smells fine, no steam and there's no contamination in the coolant.

Not sure how far fetched this is but my thought (hope) was the t-stat was stuck halfway and under load the system cannot circulate everything away from the block...then again I'm not sure how much I have convinced myself of this while hoping it's not a head gasket.

[jasnmar]

Sounds a lot like a Dodge charger I once had.

Started much like you are stating.
No noticeable exhaust problems.
Eventually started "overheating" because of blowing enough coolant out.
Next step was "steam" in the exhaust. Head gasket wasn't "cracked" but had gapped underneath between the combustion chamber and and a coolant port.
If I were betting I'd say head gasket.

Compression check should give you some information.

[Paul_E_D]

Everyone want there to be contamination, but that only when the thing is well and truly burnt through. What you are describing is how they first show up. Most people ignore it til the warp the head, contaminate the oil, etc. Just dig in and nip it in the bud. 25 bucks and a day's work

[Stoneman]

Any chance you simply overfilled the system and it's just trying to escape?

[butcher bergs]

^^
Possibly.


The machine's only got about 125hrs on it and while it's older (2003), I'd hate to think a headgasket would fail with such limited run time, which is why I want to be certain of everything else prior to conceding to a head gasket issue.

[csmutty]

Sorry I don't know how wera does it.

[butcher bergs]

Well, I have accepted that the issue is a head gasket.

Thank you guys for the help and suggestions.

[CBR929RE]

Well, I have accepted that the issue is a head gasket.

Thank you guys for the help and suggestions.

only 11 more steps to go

[stoinkythepig]

A leakdown test would be very telling. Alternatively, if you know someone with and exhaust gas analyzer, you can remove the radiator cap and have them probe the radiator opening. The EGA will detect combustion by-products if the gasket is leaking into the coolant passage.

When/if you "pull the motor", remember to support the engine from below and lift the bike off of it. I like to have the bike tires sitting on 2x6 scraps and then build a stand for the motor out of wood scraps. When you lower the bike onto the motor, use some 18" long tapered wedges (made from 4x4s cut diagonally lengthwise) under the tires to get the bike nicely aligned height-wise with the engine.

[butcher bergs]

A leakdown test would be very telling. Alternatively, if you know someone with and exhaust gas analyzer, you can remove the radiator cap and have them probe the radiator opening. The EGA will detect combustion by-products if the gasket is leaking into the coolant passage.

When/if you "pull the motor", remember to support the engine from below and lift the bike off of it. I like to have the bike tires sitting on 2x6 scraps and then build a stand for the motor out of wood scraps. When you lower the bike onto the motor, use some 18" long tapered wedges (made from 4x4s cut diagonally lengthwise) under the tires to get the bike nicely aligned height-wise with the engine.

In addition to the overflow tank issue described above, the cooling system is being over pressurised to the point where the radiator cap is not able to contain coolant. Didn't notice that detail until yesterday.

No need to remove the engine since this is an ATV. Pull fenders, gas tank and intake...plenty of room.

[Jim]

Thank you guys for the help and suggestions.

Glad I could help.

[DaveZX6r]

Your problem is your engine is getting stressed out driving 2 more wheels than it should. Get back on a bike you knob :p