Volvo MD17c water pump

[sailcruiser]

Hi all,

We are chasing down an issue with our cooling system. We have raw water system with no exhaust manifold. The issue started with no water being passed with the exhaust. I read on one site to that the output of your water pump for 15 seconds and it should be ~9.5 qts (no engine speed mentioned) I can't find anywhere to verify that info. Does anyone have an idea if that is in the ballpark?

We tested at around 2 qts at idle. While in this process we also did the usual impeller change (it is installed correctly I triple checked that), thermostat change, and are checking passages for past impeller parts.

The water pump was replaced in 2009. Is it time for a rebuild? No idea how long these go between services. That's about 150 hours.

Thx!



SC

[Acushla]

The pump should be fine for wear if it was replaced in 2009 although impeller replacement could well be required if you have overheating issues.
The engine will need approx 12 litres a min at 1200 rpm to provide adequate cooling.
Raw water cooled engines shouldn't run above 80 C as calciferous deposits will form in the waterways above this temp. The engine efficiency doesn't mind it running hotter but the salt water deposits become a problem.

[DeepFrz]

Clean the exhaust mixing elbow. That is where the cooling water cools the exhaust gas. It is also a place where impeller bits can accumulate.

Your pump should be good unless you operate in very sandy or gritty water.

You may need to back flush the water passages in the engine with pressure water or even descale the engine.

[sailcruiser]

Originally Posted by Acushla

The pump should be fine for wear if it was replaced in 2009 although impeller replacement could well be required if you have overheating issues.
The engine will need approx 12 litres a min at 1200 rpm to provide adequate cooling.
Raw water cooled engines shouldn't run above 80 C as calciferous deposits will form in the waterways above this temp. The engine efficiency doesn't mind it running hotter but the salt water deposits become a problem.

Thanks Acushla! 12 liters is roughly 12.6qts. I doubt we are quite that high. When measured with the output disconnected going to a bucket we measured roughly 8 qts/min (7.5L/min) at idle which is ~950 rpm. I will try the test again and try to get to 1200 rpm. We put everything back together last night and we are getting cooling water with the exhaust.

What has been done to date:

1 New impeller/seal and light sanding of the plate to remove goo. (no change in symptoms)
2 removed exhaust elbow and cleaned (not blocked but dirty) (no change)
3 replaced thermostat and found impeller piece of indeterminate origin probably PO as I change these annually to avoid this occurrence resulted in some water flow.
4 changed exhaust hoses (mixing elbow to muffler and muffler to outlet) the first was going bad and the latter was REALLY bad. The rubber in each had bubbled creating at least three 50+% blockages. The latter one had rubber rot. It's easy to ignore these hoses. Won't do that again. Helped water flow significantly.
5 this weekend check what passages in the engine I can get to to make sure no other impeller parts floating around.

Did I miss anything? At this point I'm mostly through so may as well complete the inspection and maintenance.

Thx!


SC

[sailcruiser]

Originally Posted by DeepFrz

Clean the exhaust mixing elbow. That is where the cooling water cools the exhaust gas. It is also a place where impeller bits can accumulate.

Your pump should be good unless you operate in very sandy or gritty water.

You may need to back flush the water passages in the engine with pressure water or even descale the engine.

Hi DeepFrz,

I had cleaned the mixing elbow but forgot to mention it. Ended up looking like I worked in a coal mine. It was dirty and needed a cleaning but wasn't blocked. We are in the Great Lakes so the water is definitely muddy but no salt or sand. I was reluctant to backflush because I had read another account where the folks managed to get a ton of water into the oil doing just that. I don't need to make more problems than I already have being a rookie mechanic.

I listed what's been done in a post above. I'm still suspicious we have impeller bits floating around of unknown age. I replace mine annually after 5 months use to avoid that happening. It is overkill but I hate chasing rubber bits.

Descaling may be a good thing too. I'll have to look into what is involved. I haven't done it since we have owned the boat (fresh water) but it probably needs it.

Thx!



SC