Diesel overheating

[Mark]

Ever since my last haul out, my engine has overheated. I'm not sure if the overheating is related or coincidental, but I have done the following troubleshooting to no avail: replaced heat exchanger zincs and dismantled heat exchanger for thorough cleaning, checked all through hulls for blockage, replaced radiator mix, replaced thermostat, replaced salt water impeller. I have not checked temp guage, but have no reason to believe it is not accurate. Before the haul out, the engine ran great at around 165-170 degrees. Now it quickly climbs to 180+ and I have to back it down to 10-12RPMs to have it hold at 180, something I can't sustain in heavier seas. Any ideas/suggestions would be appreciated.

 

[Don]

Did you "burp" it?

According to the manual, you could have an air pocket in the fresh water side. Start engine and let it warm up. Shove throttle up to 3000rpm for about 5 seconds. Temp will shoot up to around 200 and fall quickly back down. Shut it down and check coolant level. You might have to do this 2-3 times to get all the air out. I know it sounds a little weird, but I've done it my M-18 and it works.

 

[John Visser]

bleed it

You should be able to bleed the frsh water side at the top of the thermostat housing. If that's not it, I suspect you have a heat exchanger blockage. Is there a raw water strainer? Check it. Also, open the heat exchanger inpsection port (one end) and look for seaweed, pieces of impeller, etc. Mine did this until I replaced the heat exchanger. Turned out the old one had bot seaweed and pieces of impeller in it.jv

 

[Matt]

Hoses swapped?

If the hoses leading to the thermostat housing were disconnected at the haul out, you may want to verify that they went back on correctly. If they were accidently swapped, it could lead to overheating as you have experienced.

 

[Brad]

Radiator cap?

A friend of mine was having an overheating problem. The first thing he did was to simply change the radiator cap and it works fine.Brad

 

[Tim Dranttel]

New Heat Exchanger

I had the same problem with my 86 30' TR w/M25. Much like you I put in a new raw water pump, thermostat, radiator cap, zinc, and hoses. I also cleaned out the exchanger. All with no results. The only way I could keep temps from completely going off the guage was to close the valve by-passing coolent to the hot water heater. But then I did not have any hot water to shower with and it did not completely solve the problem. In talking with other M25 owners I discovered that this was a common problem and Universal when it made the M25XP it equipped it with a larger exchanger. There are several after market suppliers of this larger heat exchanger. It fits and works like a champ! Cool engine and hot showers!Tim