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Discussion Starter · #1 · (Edited)
I bought this sled this past summer, and had someone look at it recently. It had a known issue going into reverse; it would only do it some of the time. Most of the time, it would just stall when you pushed the button. So, the contacts on the switch block on the handlebars was cleaned, and relubed with dielectric grease. Since then, I have not been able to get it into reverse once. The sled stalls, and will restart and run no problem.

Also, it's turning on the overtemp light. And suggestions on where to start with that? I looked in the coolant reservoir, but can't see much. Fill hole's too small, and the tank is obscured on all sides.
 

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Very often when RER fails to engage the engine has low compression or the spark plugs are poor.
 

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Discussion Starter · #3 ·
Very often when RER fails to engage the engine has low compression or the spark plugs are poor.
Hmmm. Plugs are an easy fix, what would be considered "low compression"? And what is "good compression"?

I recently sold a newer sled (also with a MXZ 600 liquid) that the dealer said had low compression. It measured (their number) 135 and 133 PSI. That sled would go into reverse with no issue at all.
 

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Hmmm. Plugs are an easy fix, what would be considered "low compression"? And what is "good compression"?

I recently sold a newer sled (also with a MXZ 600 liquid) that the dealer said had low compression. It measured (their number) 135 and 133 PSI. That sled would go into reverse with no issue at all.
Anything under 100psi a hole generally has that stall
Check belt tensioner,plugs,compression
 

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Discussion Starter · #5 ·
Just spoke with the guy who looked at it. 130 & 132 psi. He's replaced the plugs.

What belt tensioner am I looking for? Any further suggestions?

He's recommending replace the switch on the handlebars next. I know those type of things aren't cheap.

And an update: I just got it out. Started right up and went into reverse before I'd even call it warmed up. Made it almost 2 laps around the yard before the over temp light came on. It went into and back out of reverse another 2 times. Shut it off and put my hand under the tunnel on the radiator, not even sort of warm. If it was truly overheating, it would be, right? And it looks like it has 2 radiators from the parts diagram....
 

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If the over temp light came on that quickly, it's possible that the thermostat has failed. Normally, once the engine is warm enough, the tstat opens and the coolant will circulate and you'll feel it in the exchangers in the tunnel. The other possibility is a failed water pump. Of course, there's a 3rd thing that comes to mind - a temp sensor that is out of order....
 

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Discussion Starter · #7 ·
If the over temp light came on that quickly, it's possible that the thermostat has failed. Normally, once the engine is warm enough, the tstat opens and the coolant will circulate and you'll feel it in the exchangers in the tunnel. The other possibility is a failed water pump. Of course, there's a 3rd thing that comes to mind - a temp sensor that is out of order....
Hmm, I considered the thermostat. Aren't they designed to fail in the open position, though? I had not thought of the water pump. That sounds like a super expensive fix. Any idea on how to go about diagnosing that? The guy I have looking at it seems to think temp sensor. Based on what, I'm not sure.
 

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With the thermostat, it's possible to fail in the stuck closed position I've heard. If that's the case, your engine would be very hot in only a few minutes. Same with a bad water pump. If there wasn't circulation, then the hoses would be cool while the engine block got overheated. It would be possible to run the engine without a tstat for awhile to see if that's to blame.
 

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Discussion Starter · #9 · (Edited)
With the thermostat, it's possible to fail in the stuck closed position I've heard. If that's the case, your engine would be very hot in only a few minutes. Same with a bad water pump. If there wasn't circulation, then the hoses would be cool while the engine block got overheated. It would be possible to run the engine without a tstat for awhile to see if that's to blame.
Yeah, grabbing the hose to see if it's hot or not would be an easy test. If not, take out the thermostat, and that would let you narrow it down to thermostat, if the hoses then got hot. If not, it's the pump.

If the hoses DO get hot, that would indicate a temp sensor.

Do I have that all right?

EDIT: I started it up and when the light came on, the hoses weren't warm. This took less than 5 minutes. Now, the only place I see that you can grab the hose is up near the thermostat, and down where the bigger hose comes into the back in the front. Not sure whether that's the supply or return...which way does it flow?

Either way, that indicates that the sensor is working right, no?
 

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Yeah, the hose at the back of the engine is the one that passes the coolant to the heat exchangers. The one at the front is bringing the coolant from the exchangers and into the water pump/engine. If you were to run without a tstat, the coolant will also pass into the bottle beside the cyl. head with the rad cap. When converting (ie. tstat delete) this hose would require a reducer so that the coolant is still (mostly) going to the exchangers. Bottom line is that if everything is working normally (tstat opens, coolers warm up in about 5 min.) then the problem is a temp sensor. Hope this helps and doesn't confuse!
 

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Discussion Starter · #11 ·
Slightly confused, yes. So If I want to run a valid test on the thermostat and take it out, I need to put in a reducer?

And, since I was touching the return hose at the front of the motor, does that make it an invalid test?

Out of curiosity, is there any way else to diagnose a bad pump? Should the hose be resistant to pinching it?
 

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I would try taking the thermostat out, check it for damage first. You could run without it, maybe pinch off the hose to the bottle with a clamp temporarily. See if the coolers warm up, if not then the likely issue is with the pump - could be a broken impeller or stripped gear. They are plastic and run off the crank. Not sure about other tricks to diagnose but I did run into a 2003 Summit 600 that had a bad water pump gear.
 

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Discussion Starter · #13 ·
Will do, thanks.
Any opinion on the reverse thing? A couple people mentioned in this thread that it is most often is the spark plugs fouled, or low compression. Sled has new spark plugs and 130 in both cylinders.
 

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Usually the reverse issues were related to low compression but yours sounds fine. If the belt is too tight it can cause problems. Once you have the overheating issue looked after, get the sled running with the track off the ground. With the engine at idle, the track shouldn't be turning. A slight bit of turning is ok, but if the track spins a lot then the belt is too tight and the engine will struggle to restart in reverse. In post#5 you had it going into reverse ok so we'll see what else you discover.
 

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It isn't necessary to remove the head. The tstat is removable after the hose back there is pulled off the housing. Two bolts (10mm) that go up from underneath gets that housing off and the tstat is in there. Usually the carbs have to be pulled back to do so.
 

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Discussion Starter · #18 ·
Ok, I ran an experiment. I removed the belt from the machine entirely. Started it and switched into reverse and back out a bunch of times. In about 20 cycles or so, 3 failures to change direction. (It stalled)

So according to the responses I've gotten here, a tight belt may be to blame. I know I've adjusted the secondary pulley on another machine before, but I forgot how I did that, could someone tell me? As it was, before I took the belt off, the outer belt surface was riding just above the edge of the secondary, about 1/8", maybe slightly less.

This experiment also showed another potential part of the problem. These 600 liquid engines I've seen always seem very reluctant to come back to an idle. Sometimes, if allowed to sit there long enough, the will settle back down, but it usually takes minutes. Sometimes, blipping the throttle will get them to settle sooner. As I watched the primary pulley move when I goosed the throttle, it was opening slowly and smoothly at first with the engine, and then for the last little bit, it'd snap quickly the rest of the way with a thunk. Could it not coming off of idle soon enough be part of the reason? As in, the primary is closed at a high idle, and when the motor goes to stop and reverse, the primary hangs up just long enough to pinch the belt and stall the motor?
 

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Discussion Starter · #19 ·
And today, belt back on, went into and out of reverse with no adjustments or issues several times. This problem is very hit or miss. It's almost like it's either in the mood to do it, or not.

Any possibility it could be a computer problem?
 

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If blipping the throttle will not bring the idle down try flip choke on / off, often brings the idle down quick.
 
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