500 hp heating problem

[augie58]

I have an intermittent heating problem the gauge will jump up to around 210, maybe stay there for awhile maybe drop down quickly. Sometimes I can get it to drop down by turning the motor off for a moment then restarting the motor. This condition may happen several times in a day or not at all. I am thinking I have a piece of impeller stuck in the cooling system, I have backflushed the system several times. Replaced thermostats a couple of times. Any ideas or tricks?

[MOBILEMERCMAN]

I would start by verifying the actual engine temp and check for constant water flow out the exhaust. Then check for loose wires or a bad gauge or sender. The actual temp doesn't usually change quickly. Most important don't assume it is a gauge problem and disregard the warning.

[Griff]

I had the exact same thing happening on one temp guage. I knew it wasn't really that hot. I had Gaffrig/Livorsi redline guages. The warning light on the guage would come on, but the the Merc alarm would never go off. The alrm should go off by 200*. They use different sensors.

I replaced the bad guage and all was well. Temps were identical on both engines.

[augie58]

Thanks guys

Any other suggestions? This has been a PIA for a couple of years. When the temp has spiked I have gone back and done a "touch test across the manifolds of both engines and to the touch they seemed even.

[Sydwayz]

Buy yourself a Laser Temp Gun also called a Laser Pyrometer. It's actually a VERY useful tool on a lot of things. It's excellent for keeping check on tires, brakes and bearings while towing.

[Griff]

Mine always did it on an initial cold start up. All I had to do was turn the engine off for 3 seconds and refire and it would read fine. Then it became more frequent and intermitent.

[augie58]

I am going to buy the laser temp gun just because they are such a cool and useful toy. I think for a cheater test I will flip flop the gauges to see what happens.

[donzi2287]

If you have a thermostat with a crossover pipe, make sure you have 3 5/32 holes drilled on the sides of the thermostat.