When the speedo starts flashing "HOT" the engine also starts running really crappy. It has been suggested that this is because the ECU has put the machine into "Limp Mode" that detunes the engine to protect the engine from damage.

Does anybody know if there is indeed a "limp mode" that the ATV goes into if the ECU senses and overtemp? Or is the crappy running just a direct result of the overheating?

 

we have had overheated bikes before and didnt go into any limped mode.

 

The 850 does have a limp mode for overheating at a certain temp it kicks in and reduce the power output considerably. Then at a higher temp still it completely stuts down the engine.
I'll take a look at my 800 service manual when I get a chance and see if it says anything...but if the 850 has it I'm sure it is possible the old style could as well..

 

It does, I remember thinking, "I'll get back to the truck"..but I didn't make it. It ran under 3000 rpm or so. Then it started to puke coolant out the overflow bottle breather tube, not a good day...

 

Couldn't find anything in the 500 Service manual or Owners manual about "limp mode".

 

the new ones might but pretty sure the older ones dont as people have had major engine issues from overheated engines. dont let an overheat issue get to that point thinking that it will be protected. just my .02

 

Why wouldn't you have just shut it off and let it cool down a while so you wouldn't damage the engine?

 

When an engine overheats without a "limp mode" it will go into a condition called predetonation. When this occurs the combustion happens before the piston reaches TDC.(top dead center) Your losing a lot of power because its detonation in the compression stroke and not the power stoke. It's not a good idea to run it like this. If it has a limp mode it actually goes into a rich "choking" condition because the extra fuel help protect the valve train from extra heat resulting from the less protection of the overheated oil. Not a good idea to run in this mode for long.

 

No, I wouldn't. The question is more a matter of curiosity.

Quick recap of my experience with the "HOT" indication. I thought had cleaned my radiator very well when in fact I hadn't thorughly cleaned the backside of the radiator. Additionally I had the plastic "grill" around the winch cutout installed.

Anyway, went out for a ride with a group after a while the speedo flashed "HOT" and the engine started running like crap. I called it a day and let the machine cool then drove back home. Got home - cleaned the radiatior THOROUGHLY - and removed the grill around the winch cutout. Decided to go back out - caught up to the pack - and have had no more issue with getting "HOT".

Since the I had added the quadovator temp guage as an added measure to keep an eye on the temp (and proper operation of the fan).

But I know at some point somebody mentioned that when it got hot that into went into a self-preservation limp mode that detuned the engine. I am just curios if this is what is happening or if it is as MEGA XP states that the loss is because its detonating in the compression stroke and not the power stoke.

Either way - I do not reccomend anybody continue to ride in this condition - stop - cool the machine - and find out what is going on - and correct the issue if you can. For those that are riding in mud and need to clean your rad on the trail - get a trail washer like Stendori has.

 

The "limp mode" if a machine has one, will only be on EFI machines...BUT all the EFI machines adjust fueling and ignition based on ECTs..
But IMO limp mode is a bad term and as has been elluded to operating an overheated machine is bad news..and even extra fuel and retarded timing is only going to buy you a few minutes(depending on why it is getting to hot). I will say if you can get it cooled fairly quick wihout shutting it down that is the best course of action.
The 08 700 and 800 give a HOT indication at 215*F..this should not be near hot enough to cause heat related detonation or pre-ignition. But if you are having heat related power loss,not ECM induced, the engine is very hot and you haven't done it any favors at all..
Personally limp mode is an attemp to minimize damge in the hands of someone who doesn't realize the damage that overheating can do.