Overheating 4-107

[Uncle Buck]

Hi All,

Recently my engine has started to run hot when under load (temp creeping over 190 to 200). If I throttle back to less than 1100 RPM's the temp comes down to around 160-180. Even running in gear at the dock at 1400 RPM (which gets me about 7 knots of speed on my 42' steel sloop) and the temp does not climb about 160 or so. The bottom and prop are clean and nothing has been changed.

I changed the raw water impeller (the old one was worn but had all the blades), and have gone through the raw water system checking for flow and blockages. It appears fine all the way through to where it exits the boat, and water flow out the back seems good. However, I am told the riser should be cool to the touch if raw water flow is adequate - mine is quiet warm but I can keep my hand on it easily.

Wondering if it could be the closed system? Do these water pumps fail? What about the thermostat maybe only opening partially? I am not losing cooling fluid, though I find it strange that I can open the filler cap without any pressure build up even when the engine is up to temperature.

Thanks in advance for you advice and help!

Cheers,

Evan

[svHyLyte]

How many hours on the engine? If many, you may just have a build-up of material in the tube bundle of your heat exchanger that is restricting raw water flow and the heat exchange process. Our 4-108 had about 3200 hours when we began to have similar difficulties that were solved by pulling and soaking the tube bundle in bucket of RydLyme. Also, when was the last time you changed the cam in you raw water pump? They do become worn which reduces flow quite a bit. Trans Atlantic Diesel suggests changing the cam every few hundred hours for optimal performance.

FWIW,,,

[Katrinu]

I also suggest that you clean the water cooler. The tube may get biuld up and flow of water slows down . Open the cooler and clean it. If the raw water pump plays then you may also have trouble in it.

[mike d.]

if you are not building up preassure in your closed system then you may have a bad cap. xcheck anti-freeze level when cold and hot, if way down when cold then you need to bring it up to level there should be a vent tube on your over flow pipe where cap is is your cap is allowing your anti freeze to boil out it will go to the bilge and get pumped over by your bilge pump. start withv cap and then check temp with new cap and see if it boils over. if so you need to check your cooler for debris in it. yes the fresh water pump can go bad. if that is your leak may be there, you will see it coming out the weep hole under the shaft, when the engine is run and starts to warm up. is f it is really bad it will leak out as pour in more coolant. but start with te cap first it is the cheapest

[Uncle Buck]

Originally Posted by Katrinu

I also suggest that you clean the water cooler. The tube may get biuld up and flow of water slows down . Open the cooler and clean it. If the raw water pump plays then you may also have trouble in it.

Sorry if this is a dumb question but the " water cooler " and " heat exchanger " are the same thing, right?

[svHyLyte]

Originally Posted by evanOR

Sorry if this is a dumb question but the " water cooler " and " heat exchanger " are the same thing, right?

No doubt...

[DeepFrz]

I changed the raw water impeller (the old one was worn but had all the blades), and have gone through the raw water system checking for flow and blockages.

Does this mean you have had it all apart and cleaned everything from the raw water pump to (and including) the exhaust elbow? If not, I suggest you do that before looking at the coolant side of the system.