Alright guys little story behind this... I left the mountain from snowmobiling today and about 20min into the drive I started the long trek up the 7% grade 5 miles long at 11,000ft elevation. By the time I got to the bottom of the grade my thermostat had obviously opened (Saw temps rise to 195 then backed down to 190). So, doing 70 with the EGTs at 1,100 degrees constant I look down and see the water temp rising... usually this is normal and it creeps to 195-197 then settles right in that area. This time it kept rising and topped out at 209. It then held that for about a mile, then dropped down to 195 and didn't rise again the rest of the way up the mountain. I don't think this is normal... Is my thermostat failing??

Just take note of it. Might be just a fluke. I won't jump at changing  thermostat right away.

Radiator clean? Outside air temp higher than normal for that load?

Radiator is spotless, and it was 43deg. 1100 on the EGT should be nothing for that big radiator to handle!

I wouldn't worry too much about it for now, it could just be from holding that angle and not flowing much coolant to the rear of the head where the temp sender is. The rear of the head is already sees the least flow plus add in the grade of the hill and EGTs. There's a reason high performance guys run bypasses to the rear of the head.

Edited March 23, 201510 yr by bjytech

207° is where the 190° thermostat goes full open, and since a lot of heat comes from the head the 1100° will have an effect on it. I have noticed that the opening spikes are higher closer to the first opening with a load, as the entire block hasn't stabilized yet. 

 

In short, you may have had the first opening but I doubt the temps had stabilized and the inrush of heat/load from the grade means that it took a little longer to reopen. 

 

If you start to see it more frequently it is a sign of the thermostat starting to wear out. With the large size of our cooling systems the thermostats don't go full open on a regular basis so they develop wear spots and going full open becomes more difficult over time. 

Thanks for the replies guys! I'll keep an eye on it and report if it acts funny again. I think when the motor comes out she's going to get a 200 T stat though.

Thanks for the replies guys! I'll keep an eye on it and report if it acts funny again. I think when the motor comes out she's going to get a 200 T stat though.

 

I would only go that route if you don't tow, otherwise any benefit from the added temp will be lost by additional fan operation. 

I would only go that route if you don't tow, otherwise any benefit from the added temp will be lost by additional fan operation. 

Good point... it's not a tow pig. I haul around my antique tractor to shows and pulls during the summer, some hay hauling now and then, and snowmobiling during the winter. My clutch never engaged when it was at 209?? I wonder if a fan clutch from a 3rd gen would fit it?

The fan clutch on a 3rd gen is electronically controlled by the ECM. 

 

If the clutch on 2nd gens is still a true mechanical clutch then it wouldn't have engaged, as the temperature coming off the radiator wasn't high enough to engage it. 

Well I think the thermostat is shot... Went and picked up the sleds today and it keeps running up to 198-200 on the small hills.

I think when the motor comes out she's going to get a 200 T stat though.

Why you pulling the engine?

The bed and topper are getting painted, and my paint guy takes his time. So while he has those parts I'm going to pull the engine and figure out what the heck the knocking sound is. Then I'll clean up the bay with paint, paint the engine, reseal the engine, wrap the wires in all new plastic, and stuff it back in the hole. If money permits it might be getting a new cam as well