Overheating Volvo MD3b

[Bambolera]

I don't know what to do. Please help.

I've already tried the following:

1) changed water pump
2) replaced all hoses
3) changed thermostat
4) checked anti siphon valve
5) checked raw water strainer

I fear that the engine water channels are blocked. Is there any way to clean the inside of the engine? It's raw water cooled and it might just be salt buildup. Any ideas?

John

[NCboatrx]

If you have silt and salt build up in the water passages, the only way to fix this is the remove the manifold, cylinder heads and cylinder barrels and have these parts properly cleaned out.
Reassembly will obviously require new gaskets, rings etc.
Stanley

[Vasco]

Some folks remove the thermostat and suck in vinegar or muriatic acid and let it sit overnight.

[Cheechako]

How much water is coming out the exhaust? Another cause of overheating could be the exhaust elbow is getting blocked ...?

[Bambolera]

Thanks for your responses.

Today I removed the raw water hose from the reverse gear (the first connection in the system) and hooked it up directly to the water pump. I started the engine and everything is working perfectly.

Now I know the problem is in the reverse gear. The water channel is probably blocked or (at the very least) restricted. I want to try soaking it in something. Vinegar sounds like a good idea, but would it be strong enough? I also have some pink stuff I used to clean my A/C evaporator coils?

[Outwest34au]

Hi mate,
I am not totally picturing what setup you have there but may I suggest a simple test.

With the engine at moderate to high revs look at the intake hose and ensure it is not sucking itself together. Some hose require a spring to keep them from collapsing.

[Dsanduril]

Ahh, this brings back memories. Our MD2B was configured identically. In the reverse gear/transmission there isn't much heat, our experience was that it was growth of marine life rather than mineral scaling.

For mineral scaling you can use vinegar but it will take a long time (if you can keep it hot that helps) or muriatic acid (available at a hardware or pool supply). You have to use more care with the acid, both for yourself and the equipment. If you can figure out a way to circulate either that will help speed things along. Alternatively, a commercial de-scalant (ALPACON DESCALANT, Alfa Laval), while harder to find may do a better job.

For marine growth we were able to rod and wire brush the water passage in the gear. Get yourself a flexible wire brush about the diameter of the hose and push it through. Takes some work, but it can be done. The coolant housing is a loop, so the curves make things difficult, but if you work from both the inlet and outlet side you can usually get it cleared out. Make sure you flush it well so that your loose crud doesn't end up in the engine passages when you re-connect things.

I would recommend also looking at the water passages in the exhaust elbow at the same time. It's pretty easy to do, and even if you have good water flow now if the tranny is plugged then it is likely the elbow could use a little cleaning as well.

Outwest (and anyone else confused),

On the Volvo MD series with raw water cooling the water comes from the seacock, passes through cooling channels in the tranmission/gear, and then goes to the water pump inlet. As a result the tranny cooling is on the suction side of the pump, which means there isn't much head available to overcome blockages (such as barnacles/muscles that decide to grow in there). The OP took the tranny out of the loop and everything was then OK with the engine (but the reverse gear is no longer cooled).

[Outwest34au]

Thankyou very much for explaining that so clearly for me Dsanduril.

[Bambolera]

Originally Posted by Dsanduril

Ahh, this brings back memories. Our MD2B was configured identically. In the reverse gear/transmission there isn't much heat, our experience was that it was growth of marine life rather than mineral scaling.

This makes, too much, sense. I have a very large Graco raw water strainer (with the thinking that bigger is always better), but I never considered the idea of marine growth inside the engine. The strainer has a coarse mesh; even small fish could pass. Of course it wouldn't matter if the heat (from running the motor) were enough to killed the growth, it would likely just build up between uses anyway.

Sounds like I have a coral reef growing in my motor. I better exterminate it quick, before the environmentalists find out and try to save it.