View Full Version : Another overheating issue

04-07-2007, 10:49 AM
My brother and I both have Mastercrafts. His is an 85 S&S with a 351 PCM. It has been having overheating issues. We replaced the impeller and the thermostat (160 degrees) It is still heating up. It seems to not overheat as bad when the boat is idleing. When you start to accelerate it heats up around 225. It will come back down a little when you slow down. I already did the 5 gallon bucket of water test. Filled it up in 15 seconds at 3000 rpms. I couldn't find any blockages. Water shoots out the back of the boat no problem. Any ideas?


04-07-2007, 11:34 AM
Replace your temp sending unit, possibly faulty. Head gasket leak is another possiblility.

04-07-2007, 11:42 AM
Check the condition of your coolant cirulating pump as well.

04-07-2007, 12:21 PM
I forgot to say that I did replace the sending unit already from DIM. Is there a way to check the gauge? How about the circulation pump? How do you know if that is bad if it is not leaking? Also we rescued this boat from a saltwater environment if that gives any clues.

04-07-2007, 12:32 PM
The engines (circulating) water pump impeller is made of steel...

With exposure to salt water, I would be curious to see how it looked?

You will need to remove it from the engine to inspect it.

04-07-2007, 04:20 PM
does it have a heater?if so check the y-connector restrictor

04-07-2007, 05:37 PM
It doesn't have a heater.

04-10-2007, 09:56 PM
I just ordered a new circulation pump for my brother's 85 S&S. I hope that fixes the problem. If not anyone got any other guesses?

04-10-2007, 11:39 PM
Just for yuks, you may try removing the t-stat altogether. I have seen new t-stats bad right out of the box. See if the engine stays cool then.

88 PS190
04-10-2007, 11:48 PM
normally when i see failed thermostats they fail open, and then it doesn't warm up (overcooled)

In order, I check impeller, plugged colling passages, flow out the exausts, do you get a fair amount of water?

If the head gasket is having trouble you might see fluid in the oil/milky oil.

check grounds and connections for temp sender, corrosion etc.

I'm sure there are specs for the sender and gauge for resistance and readings, I don't have them.

The shop I worked at had some mechanical gauges and senders that we'd screw in when we were trying to diagnose weird findings.

04-13-2007, 06:17 PM
Well I put the new circulation pump on and still having the same problem. Noticed that the driver side of the engine's exhaust manifold was extremely hot and not a good amount of water runing out that side. Took the exhaust riser off and found that I have some blockage issue in there with not letting the water run out the back of the boat. Do you think this could cause the boat to still overheat?