I was on a run yesterday and the hot light started flashing. The fan is working properly, and seemed like plenty of cool air was getting sucked throught the fan. If it was really hot I would expect the air too be fairly warm. There was some mud on all the fins but not enough to stop any flow. The rad was full and I took the cap off, it was too hot to put my finger in but not boiling. Is this a sensor problem? I drove it with the "hot" flashing for 10 inutes and then took the cap off, if it was really hot I would have expected the coolant to be boiling and spray everywhere. Also can you add either and electrical or mechanical temp gauge to these, where could you put the sender. Also it was a cool day, approx 5C/40F.

 

I'd flush the outsides of the radiator and even if it looks clean,could be stopped up around the fan area not allowing it to pull air in enough. Its easy to remove the fan motor assembly to really clean this area well. Plus leave the radiator cap off when you crank it back up to purge any air,plus helps if you have the front end jacket up. Trapped air and dirt/mud are the number one cause of overheating problems,especially if the fan works properly! OPT

 

were both radiator hoses hot, warm or cold? could be the impeller on the water pump came loose or off and it's not circulating water, thermostat could also be stuck closed.

 

Thanks for the replies guys but I am more interested in whether or not it actually was overheated. Does the fact that I could open the rad cap and not have any boiling or overflow
indicate that it really was not over heating and possibly just a malfunctioning sending unit? Even if impeller or thermostat were malfunctioning and the coolant in the block was overheating then it should still have boiled over out of the cap?

 

Just leave the radiator cap off, warm it up until the fan cycles on. You can see if the coolant is circulating in the radiator. If the coolant level goes down when the fan cycles on,doesn't boil over, and no hot light,then its possible you just had some trapped air.Anythings possible about the sensor,etc,but just try this first,especially if you know for sure the the radiator is clear front and back!! Just take one step at a time! OPT

 

i worried my self to death bout my 400 when i first got it so i cleaned radiator fens real good an installed a regular auto meter temp gauge where sending unit is in back of head,...an wired up the light to come on an off with fan motor,..rarely see temps above 180,..fan come on round 190 only when climbing long grades,..most time we belly button deep in the creek an its peggin cold!!

 

Could you explain more about the sending unit. Is the stock one in the head that triggers the "hot" light and you just replaced it with an auto meter one? If so did this disable the "hot" light? I did some googling and apparently a lot of people tap their thermostat housing for their sending unit, I don't know what engines this applies but I think the 700 and 800 actually have a flat spot cast into the thermostat housing which seems like it was designed for a sending unit.

 

yes the one that triggers the hot light,..i bought enuff brass fetting to plum in the sending unit an a temp gauge...worked out good!