over heating

[Escapade]

have a 1964 41' double cabin with Crysler (actually mitsuishi) diesel engines. I am over heading on both engines. They both go up to about 230 degrees and higher. When I push the engine to 2500 rpms under load they drop below 200 degrees, but when I go back under 2500 rpms the temp goes back up.

I replaced one of the thermostats and then test both the old ones by boiling and the opened well before the boiling point. I inspected the impellers, which are fine, and I am getting very good water flow.

Looking for ideas on what it could be.

 

[Pascal]

start with the basics. Impellers, strainers, outside scoop. open the strainer and the seacock and make sure you get enough flow coming in the boat to eliminate something stuck in the seacock (happened to me recently on a genset intake.)

after that, check the heat exchanger inlet to make sure no impeller pieces are stuck there.

also, check the belt, make sure it's not slipping at low RPM whcih would explain why at higher RPM you get enough flow and cooling.

 

[REBrueckner]

Consider what might go wrong on both engines at about the same time.....pick from Pascal's list above....thermostats would be unlikely, for example....check the simplist/cheapest/easiest things first.....make check list, order it, and go thru item by item.....
Coolant level ok??? coolant circulation??

Also consider any recent work done on both engines.

Maybe you recenly traveled thru some seagrass or other flotsam and picked it up in both inakes?? apparent water flow is really tough to gauge by eye....

 

[Avenger]

Don't forget you have two water pumps on those engines, raw water and fresh water. Make sure you check belt tension on both (I'm assuming the FW pump is belt driven, I've never seen a Chrysler-Mitsu) fresh-water pumps are known to fail as well, just not as often as sea-water pumps. Just a thought.

 

[Escapade]

Good thought on the second pump. not really sure how to get to the fresh water. checked my belts and there are all tight, impellers new, exaust water flow is strong. Second pump is what I will be looking at today.

still open to ideas

 

[Will]

Did this problem start suddenly or gradually over a period of time?
Will

 

[REBrueckner]

Post #6 asks an excellent question.....one of the first things I wondered....diagnosis would be VERY different depending on your actual experience....

...were the impellers "fine" as in your first post or "new" as in your last?? BIG difference....
Here is why that is so VERY important: If you are using the same impellers as your last trip when everything was ok, say 180 degrees, it's unlikely both impellers would fail simultaneously. I would NOT look there first; But if you recently REPLACED both impellers and now are on, say, your first few hours of use and your FIRST experience with overheating, impellers would be my FIRST suspicion....some impeller blades can crack in the first few hours of use...blue BARCO impellers did that some years back...I would never put that brand in an engine...

Also, I mentioned coolant circulation in my previous post because Pascal did not...on many engines when operating at normal temps, you can see the coolant circulating via the radiator cap hole....it's VERY doubtful both engines coolant pump began to fail simultaneously...unless you had work done on them recently.....??

the more you tell us about ANY recent work done on the engines and the more observational information you provide, the better the advice you'll receive....for example, you did not change coolant in both engines recently, right?? too much antifreeze, too little water, when refilling for example, could be a problem...as could possibly air pockets in your cooling system which must be bled.....

So you need to pay close attention to each suggestion and explore the consequences.....we cannot do it remotely...all we can do is offer advice based on your explanations/observations....
good luck....

 

[Escapade]

Did this problem start suddenly or gradually over a period of time?
Will

Gradually. I am betting now it is the water pump - but where to find parts for a crysler CM655 engine

 

[34Hatt]

Have you checked the bottom and running rear it could be fouled??

 

[Will]

The problem having developed gradually over a period of time leads me to think your heat exchangers may be clogged with debris or scale. You can have problems on either the coolant or raw water side. Maybe they need to be boiled out.
Will

 

[REBrueckner]

Escapade, by leaving out that little tidbit ("gradually" you can now forget most of the advice..mine included....