Volvo MD11C Overheating issue

[SailMaster]

Hello all,

We have a new to me MD11C. She starts quickly and runs like a sewing machine once she is warmed up. However, it will take about 10 minutes at idle and she will, eventually, overheat. We have changed the impeller, made sure full water flow is getting to the pump and flushed the cooling system with barnacle buster. Is there anything else I need to look at? This is a raw water system.

Thanks in advance.
SailMaster

 

[JoeWhite]

Thermostat

 

[Ralph Johnstone]

made sure full water flow is getting to the pump

Are you able to see how much water is coming from the pump as seen in the exhaust discharge ?

 

[SailMaster]

I now know that we are not getting full flow. We removed the thermostat and found it to be an original unit. Whats worse is that there was hardened crap on it. That is an indication of what’s inside. My next check will be the return line and the siphon break to see if that is clogged up.

Any other ideas?

 

[Ralph Johnstone]

I now know that we are not getting full flow.

And that's indicated by the lack of water in the exhaust ?

Any other ideas?

Just a matter of your clearing out the clogged water passage. We'll wait for the good news .

 

[Mark Maulden]

put the t-stat in a pan of water on the stove with a thermometer and see if/when it opens. Then clean it up with salt away and do the same. If you are sure everything is clean from the thru hull to where it enters the engine’s cooling system and it still overheats, you are now probably into removing the manifold and having it cleaned out. Any radiator shop should he able to do it or a machine shop. If the manifold is plugged up, then you are into removing the heads and cleaning them out and worst case is the cylinder jackets…on salt water cooled engines, the temp should not exceed 155F to keep the salt from precipitating out and plugging up passages. As an afterthought, make sure the exhaust hose is not coming apart internally and blocking flow.

 

[jssailem]

As an afterthought, make sure the exhaust hose is not coming apart internally and blocking flow.

Spot on Mark. One of the discoveries on my boat was water from the exhaust backed into the exhaust manifold. Built up salt deposits and eventually killed the engine. Granted it was 50 years old and had seen some hard years.

The check is well worth the time. Water has a way of finding your boat’s weakness and taking advantage.

 

[SailMaster]

Hi Guys,
So I have pulled the thermostat after much struggle. This motor had the original t stat it seems. Both bolts were a bitch to get out. The Tstat was crusty and had that hardened mud crap all over it. Water flow is improved but we are still overheating. Next step is to flush with rydlyme or barnacle buster and a bilge pump running a closed circuit for several hours.

My next question is, which hose at the exhaust to I pull and run back to the bucket to bring the dirty exhaust water back?