Cooling system help

[oscarhuanga]

Hi there. I am wondering if someone could offer advice on a cooling issue I am having. I have a volvo penta md11d closed coolant system engine that is overheating. So far I have rebuilt the circulation pump, rebuilt the freshwater pump, cleaned the heat exchanger, disassembled, cleaned out and reassembled all coolant lines, checked the thermostat, and installed a freshwater filter (did not have one).

The engine still overheats under load. Freshwater is running through the system without any issue. My guess is there must be a coolant blockage somewhere else. Does this make sense? I'm stumped.
If so, any idea how I can clear this blockage?

Much thanks.

[Bleemus]

Are you sure your not over propped?

[DeepFrz]

Did you remove and inspect/clean/replace the exhaust injection elbow?

[NYSail]

New situation or always happening?

[NYSail]

I am not familiar with the Volvo but how is your mixing elbow. A coked up Yanmar mixing elbow will cause overheating.. even though it may “look” like typical flow from exhaust it may be hindered causing overheating.

Greg

[oscarhuanga]

Thanks for the feedback. I took a thermal imaging gun to the engine and figured out that the coolant was not circulating at all (and the heat exchanger was staying cold).

Turns out they put the old impeller back in the newly rebuilt circulation pump and it spins freely (i.e., not with the shaft) most of the time. Bizarre. Looks like its back to the rebuild shop to get it done right.

[glovisol]

I have had a fresh water cooled Volvo twin cylinder MD11C for 36 years. This motor has two water pumps: the sea water pump is driven by the motor, is at the back and does have a rubber impeller which MUST be replaced every year if you wish to avoid trouble. Output from this pump goes to the heat exchanger, from here to the vacuum safety valve and from here to the exhaust elbow and back to the sea. If the rubber impeller breaks into pieces, some can lodge into the pipes/heat exchanger and give no end of trouble.

The fresh water pump is mounted on the motor's front, on a bracket tied by the starter motor bolts and is driven by the motor's rubber belt. This pump has a steel impeller and never gave trouble to me. Freshwater cools the heads and the motor block and goes in and out of the thermostat in the exhaust manifold, after being cooled by the heat exchanger. After long use some exhaust greasy dirt can lodge into the small channels of the manifold, especially the front cylinder's (CYL # 1) and reduce the cooling water flow. You will see temperature going higher by degrees, as time goes by, the more so because the temperature sensor is placed near Cyl. #1. If you suspect this, order two spare plugs (ice relief) for the manifold, remove the plugs, clean it all, then re-install with the new plugs.

[Nicholson58]

Originally Posted by oscarhuanga

Thanks for the feedback. I took a thermal imaging gun to the engine and figured out that the coolant was not circulating at all (and the heat exchanger was staying cold).

Turns out they put the old impeller back in the newly rebuilt circulation pump and it spins freely (i.e., not with the shaft) most of the time. Bizarre. Looks like its back to the rebuild shop to get it done right.

Sounds like they lost the key? I don’t know your engine. On our Westerbeek it is very easy for the key to fall out of place when installing the impeller

[glovisol]

Speaking for the Volvo MD 11C or D, it is not a question of lost key. The impeller is rubber outside, but it has a small brass cylinder between the rubber and the shaft. If this comes loose strange things happen: at certain revs the pump works normally, at other revs the impeller turns slowly or does not turn and the motor heats up: so it is difficult to understand what causes this intermittent behaviour...until you change the impeller.

Another problem is with the two oil seals back to back on the pump shaft. There is a drain hole between the two oil seals. If the oil seal breaks, than you have oil in the sump. If the water seal breaks, then you have seawater spilling thru the hole...

[Dennis.G]

I had a recent Johnson raw water pump failure (not a Volvo) where the pump shaft has a geared section (goes into engine block) that is press fit to the pump shaft. The press fit has no key or spline, and the fit loosened so that the two shaft sections did not rotate together. Had a machine shop drill a hole through fitting and drive in a pin to lock the two sections together.