View Full Version : over heating at idle

06-03-2008, 08:09 PM
I took my boat out a few days ago & she ran like a charm except the temp would go way up at idle, increase the engine speed & she cooled down .I pulled the thermostat & it seems to work ok ,I also pulled the impeller out thinking maybe it was falling apart but it looks great. I looked through the hoses & all seems ok there.

What else should I be looking at besides a new boat?

It is a 1987 PS 190.

06-03-2008, 09:12 PM
Take a look inside the transmission cooler. There is a screen that sometimes gets blocked with weeds or other material. You may have a weed that is creating enough of a blockage that at idle it can not pull water past, but when the impeller pushes more water at higher speeds it is ok. Thats the only thing I can think of.

06-03-2008, 09:37 PM
I already checked the tranmission cooler while checking the hoses. I'm hoping it was my thermostat that got jammed a little from siting idle all winter. I put it in a pot of boiling water to test it & that may have solved the problem. I'll know for sure next time she goes in the water.

Thanks for the input:)

06-03-2008, 09:43 PM
Did you remove the hoses from the raw water pump when it was winterized? If so, were they put on in the same position as when they came off?

06-03-2008, 11:13 PM
Maybe an issue with the thermostat. Those symptoms sound like they run in line with the thermostat sticking.

06-03-2008, 11:37 PM
When you pulled the impeller was it bent into the shape of place it is in or did it immediately turn back into a star, no curves, all the petals straight out?

If not the impeller is showing signs of fixing to stop working.

Does anybody make a water preasure gauge for the water intake to the motor? I want one and I will make one if nobody has it. Even throw in an delayed on crank idiot gauge to stop the motor if raw water is not comming in fast enough.

I'll do it! Watch out now - I almost lost my 454HO cause of it..... Dare me why don't ya'.

06-03-2008, 11:43 PM
If you get around to trying another T-stat and nothing changes...

I would pull the engine's circulating water pump off and take a good look at that impellor for signs of corrosion. They are a centrifugal design type and if it was rusting away could explain why it cools better at higher RPM's...

06-04-2008, 03:40 PM
Brent, I had the same problem you are describing with my 99 Prostar. I checked everything, replaced the impeller, thermostat, pulled all of the hoses and still had the overheating at idle problem. I took it to the dealership and the tech pretty much rechecked everything I had already done. The problem ended up being the impeller cover. The cover had some wear on it and was causing impeller to loose vacuum at idle speed. I have not had a problem since, Rich

06-04-2008, 04:55 PM
Thanks for all the input. I'll tighten the impeller cover & let you guy's know how she works when time ,weather & family are all aligned.:)

06-04-2008, 05:40 PM
Does anybody make a water preasure gauge for the water intake to the motor? I want one and I will make one if nobody has it. Even throw in an delayed on crank idiot gauge to stop the motor if raw water is not comming in fast enough.

Hmmm...I don't know if a pressure gauge would be useful. I strikes me that these are volume pumps rather than pressure pumps. It's gotta be a pretty low-pressure system, so I would think you'd get far better information from a flow meter.

Bruce Carr
06-05-2008, 10:31 AM
If the impellor is good, check for leaks in all hoses/connections on the suction side of the pump all the way to the thru hull fitting. Could have a leak/ loose hose on the trans cooler also (make sure the drain plug in the trans cooler is tight also). When the boat is underway, the suction side of the pump is presurized by the ram effect of the water passing by the water pick up port on the hull. At idle, the raw water pump has to suck the water up above the static water level and any vacuum leak will allow air into the pump instead of the cooling water.

06-05-2008, 05:24 PM
The drain nut had room to tighten on the Transmission cooler ,so that may well have been the cause of the overheating at idle.

I love this board for stuff like this.

Thanks so much.:)

06-06-2008, 01:03 PM
Brent, just check for signs of wear on the inside cover, if it is worn replacing it may fix your issue. Rich

06-06-2008, 01:52 PM
After the engine has been run a little, feel the back of the raw water pump. If it is warm, it is not circulating water. The impeller may "look" good but the shaft seal may be allowing air past it. Air is easiser to move than water.
If the pump is not moving water, it will generate heat. You will be able to feel it. Also, the sound of the engine may "seem" louder" than normal. Water helps to muffle the noise, and if the pump is not working well this will also be a symptom.
Additionally, the temp comes down when under power because there is a ram effect at the hull water intake. Pressurize this area and water will flow. Fake-A-Lake will also show it as operating normal due to garden hose pressurization.

Bottom line is that if the pump is getting warm, it's drawing air. Replace the pump.