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Yamaha viper thermostat

alpineviper

alpineviper

Pro
Joined
Aug 24, 2014
Messages
154
Age
40
Country
Canada
Snowmobile
Alpine Turbo Viper
anyone ever have problems with their thermostat on a viper? My viper runs fine while cruising down the trail but when heavy in the throttle it starts over heating (90deg Celsius) it recently just started doing this. The bulkhead cooler is suffice when cruising but when time for rad to kick in it doesn't. My engine has low compression pistons and forged rods. Alpine turbo kit at 12 psi. 50/50 c12 with premium. The rad won't hardly melt snow when engine temp is 90deg Celsius. A friend has the identical build and his rad is full of steam from melting snow. Any ideas besides the thermostat?
 

Assuming the basics (water pump is working and circulating properly and system properly bled) this sounds like classic head gasket failure. Yamadog just went through similar situation although his was a high comp engine. Combustion gasses pass to cooling system and create an air lock as well as excess pressure. Heavy throttle=high boost/high cylinder pressure.

Did you use studs or bolts for the cylinder head?

I guess it would be worth trying a new thermostat, but we just don't see people having issues with the thermostats. Also from what I understand they are non existent in the supply chain. Whether that is due to hidden high demand or lack of demand remains to be seen.
 
Last edited:
TD Max said:
Assuming the basics (water pump is working and circulating properly and system properly bled) this sounds like classic head gasket failure. Yamadog just went through similar situation although his was a high comp engine. Combustion gasses pass to cooling system and create an air lock as well as excess pressure. Heavy throttle=high boost/high cylinder pressure.

Did you use studs or bolts for the cylinder head?

I guess it would be worth trying a new thermostat, but we just don't see people having issues with the thermostats. Also from what I understand they are non existent in the supply chain. Whether that is due to hidden high demand or lack of demand remains to be seen.
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It has head studs with lowered compression. Yamadog had stock compression (higher). Seems odd that I can ride all day and it won't get hot until I pin it.
 
If you are not circulating water to the rad it can really only be one of 3 things:

1) water pump not functioning I'm not sure if the water pump can slip or strip
2) thermostat
3) air lock in the system This can make the other two look bad.

When you pin it you make peak cylinder pressures. Head gaskets can leak in one direction and only above a certain psi combustion pressure. The other wild card is the workmanship of the install.
 
I agree with you. I think it's airlocked. If head gasket it would push coolant into the overflow and push the rubber plug out. The rubber plug is easy to remove and would easy get pushed if building pressure.
 
alpineviper said:
I agree with you. I think it's airlocked. If head gasket it would push coolant into the overflow and push the rubber plug out. The rubber plug is easy to remove and would easy get pushed if building pressure.
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That's what one might think but au contraire Pierre!!! I just wasted what little season we had screwing with rad caps and thermostats and it was a head gasket. Mine would only push about 1 cup of fluid into the overflow after a good WOT burst and was not noticeable with the body work on and by the time I would get it off the engine cooled and sucked the cup back into the system so it looked full at the cap but the air lock created would not allow it to cool .
 
Yamadog said:
That's what one might think but au contraire Pierre!!! I just wasted what little season we had screwing with rad caps and thermostats and it was a head gasket. Mine would only push about 1 cup of fluid into the overflow after a good WOT burst and was not noticeable with the body work on and by the time I would get it off the engine cooled and sucked the cup back into the system so it looked full at the cap but the air lock created would not allow it to cool .
Click to expand...
Could you drive it all day without it getting hot? I can go all day at 6-7000rpm.
 
Here is a video of last ride last season. I rode 60 some miles behind 2 lowly Pro S 800's and never get into it throttle wise. Just after the video ends I turn onto rail grade punch it and go 1 mile. It pushes just a bit out into the overflow and overheats at WOT and shuts down no warning. after an hour it fired back up and rode it another 20 some miles with no problems. Did not know what was going on and made no sense. 1st ride this season was week after New Years. rode 20 to 30 miles on the Thursday night at -14 F no problems. Got up the next morning went 30 miles and it overheated and shut down. Ending the trip and sending me home. Everyone including Allen Ulmer said no way head gasket! it was the head gasket. A breach the size of a mechanical pencil lead from cylinder wall to 1 water jacket in the block and it only opened up probably on over boost when letting off he throttle after WOT burn.


Head Gasket2.jpg
 
Interesting. Just replace the gasket and good to go? Stock compression?
 
I never let mine get above 90deg Celsius (194deg f ).
 
Yamadog said:
. Everyone including Allen Ulmer said no way head gasket! it was the head gasket. A breach the size of a mechanical pencil lead from cylinder wall to 1 water jacket in the block and it only opened up probably on over boost when letting off he throttle after WOT burn.
Click to expand...

Almost everyone ;)

I get this a lot on the diesel side of things. Lots of denial yet in the end...
 
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