Md17c over heating. Help please!

[Stephen Ashmore]

Help wanted please!

LM30 with fresh water cooled Volvo MD17C.

Last summer the engine overheated and seized. (I wasn’t at the helm!) We managed to sail back to the marina and the engine started when cooled.
I changed to water pump">raw water pump as I had a spare, changed the thermostat. Oils OK.
Ran engine in gear for 35 minutes temp gauge normal no loss of coolant.

Next trip down checked coolant and header tank empty (Airlock?)

Ran engine under load for 40 minutes temp gauge normal but white smoke (steam?) from exhaust when at operating temperature, not before.
No overheating, no loss of coolant.

Ran engine under load for 45 minutes no overheating, no loss of coolant still white smoke when up to temperature as previous.

Serviced and cleaned heat exchanger. CO2 head gasket test kit shows no exhaust gas in coolant.
No overheating, no loss of coolant.

So we were hoping all was OK.

After several months of not being able to visit the boat we ran the engine under load in April. Very little water from exhaust. Water intake was blocked with weed so flushed out with dinghy pump in strainer. Water flow normal now,

But, the engine overheated in 5 minutes. Did not get to boiling point. No loss of coolant.

Changed impeller in case lack of raw water had caused a problem.

Ran engine again still overheats after 5 minutes raw water flow normal.

Could this be another airlock?

Should I try with no thermostat to see what happens?

Completely stumped now, so would be grateful for suggestions.

[Cheechako]

Not sure how this would figure into your problem as you ran the engine fairly long time at the dock, but: After some engine work I once had an air lock in the thermostat chamber. Meaning the only thing around the thermostat was air. As such it didn't let water flow because the t'stat didn't open and the temperature sensor was also in air! So the gauge didn't read overheating either. But the engine was VERY hot. I solved it by removing the t'stat housing and filling manually with water under the t'stat. Then when started, the water warmed and the t'stat opened properly. (Perkins engine)

[Stephen Ashmore]

Sorry, I think I have posted this in the wrong forum. Have re posted to engines etc.

[Bill Seal]

Change the heat exchanger connections so the raw water goes in the bottom and out the top so the system will be self bleeding.
Why do the Swedes hate us so much.

[Stephen Ashmore]

Originally Posted by Bill Seal

Change the heat exchanger connections so the raw water goes in the bottom and out the top so the system will be self bleeding.
Why do the Swedes hate us so much.

Why do you think the Swedes hate you? I don’t understand.

[Bill Seal]

Why else would they design the green monster hiding in the engine dungeon?

[El Pinguino]

When did you last flush the coolant side of the system?

[Stephen Ashmore]

Originally Posted by Bill Seal

Why else would they design the green monster hiding in the engine dungeon?

I’ve called much worse than the green monster!
Can’t use language on here though.

[Stephen Ashmore]

Never flushed the fresh water system. I never imagined it needed flushing. I’ve never flushed my cars.
Thanks. Worth considering.

[El Pinguino]

Worked for me on my MD17D once.

[Adelie]

Welcome to CruisersForum!

I would suggest updating your profile with your general location and your boat make & model or “Looking” in the "Boat" category. This info shows up under your UserName in every post in the web view. Many questions are boat and/or location dependent and having these tidbits under your UserName saves answering those questions repeatedly. If you need help setting up your profile then click on this link: https://www.cruisersforum.com/forums...ml#post3308797

I would happily help more if the link above is not enough.

The OP's particular question would probably be better in the Engine subforum. If they want I can move it for them.