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Old 02-10-2013, 23:01   #1
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Penta MD11C cooling question

Folks,

As a newbie, one of the mantras impressed upon me by all and sundry is to check that there is water coming from the exhaust when the motor is first started.

I have duly done this and have had several anxious moments when finding that it does not appear to be thus.

My boat has an MD11C fitted and looking at the workshop manual the water flow diagram seems to suggest that the only outlet for the water is from the thermostat housing. This would suggest that there would only be water passing into the exhaust when the engine has reached minimum thermostat opening temperature. That in turn suggests that no water goes through the gearbox until the engine is warm.

One of my friendly locals in the marina thought that there must be a bypass but I can't see one in the diagram or indeed on the engine itself.

I have seen water coming out of the exhaust when the engine is warm...

In addition to this worry is that the temperature gauge moves up and down when the boat is motoring along. It never goes too hot or too cold but seems to cycle around a point which would be at the top of the gauge. I could rationalise this as the thermostat opening when the motor gets warm and then closing again as the flow of cold sea water replaces the hot stuff but I'm not 100% sure...

Is this correct? Or is it a sign that the thermostat is on its way out and should be replaced?

Cheers,
Dan
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Old 03-10-2013, 01:04   #2
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Re: Penta MD11C cooling question

Dan,

There are two paths for the cooling water to flow. If you take a close look at the diagram you will see a solid line that goes through the thermostat and a dashed line that bypasses the thermostat. Both line merge at the cooling water discharge fitting.

The most likely cause of your problem is salt buildup in the thermostat housing. This condition will restrict water flow when the thermostat is closed. This can be cleaned up by removing the thermostat housing and soaking it in an hydrochloric acid (~15%) based toilet bowl cleaner.

I've had to do this on my MD17D.

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Old 03-10-2013, 01:17   #3
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Re: Penta MD11C cooling question

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Originally Posted by Viking Sailor View Post
Dan,

There are two paths for the cooling water to flow. If you take a close look at the diagram you will see a solid line that goes through the thermostat and a dashed line that bypasses the thermostat. Both line merge at the cooling water discharge fitting.

The most likely cause of your problem is salt buildup in the thermostat housing. This condition will restrict water flow when the thermostat is closed. This can be cleaned up by removing the thermostat housing and soaking it in an hydrochloric acid (~15%) based toilet bowl cleaner.

I've had to do this on my MD17D.

Now that you point that out the diagram makes a lot more sense!

I'll pull the thermostat housing off and see what it looks like inside.

Thanks heaps!

Cheers,
Dan
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Old 04-10-2013, 16:57   #4
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Re: Penta MD11C cooling question

When you have the thermostat out for cleaning, put it in a pan of water and slowly raise the water temperature. If you have a candy thermometer check for opening temp. It should open well below boiling. I believe Volvo thermostats are typically 140 degrees F. You probably should check and clean any electrical contacts for your gauge, since engine temps normally do not go up and down very rapidly. Good Luck _____Grant.
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Old 04-10-2013, 17:11   #5
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Re: Penta MD11C cooling question

this is a raw water cooled engine with a thermostat?
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Old 04-10-2013, 17:32   #6
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Re: Penta MD11C cooling question

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Originally Posted by Cheechako View Post
this is a raw water cooled engine with a thermostat?
Yes it is.

I took the thermostat housing off yesterday and sure enough the bypass passage was blocked with solid gunk. So I cleaned that out. I also checked the thermostat by heating water in a kettle to less than boiling and watching for it opening. I also replaced the crimp fitting on the end of the temperature gauge wire because half the strands of wire were broken.

Once it was all back together I ran the motor under load until the temperature settled and I noted a few things.

Firstly, the temperature settled a fair bit lower then the peaks it had been reaching.
There was no fluctuating of the temperature gauge
The hose from the thermostat housing to the exhaust was not as hot as it was.
Water issues from the exhaust almost immediately after starting.

So I think the thermostat is operating properly and the real issue was the blocked bypass passage...

..and now I have another couple of symptoms that I can look for to make sure it doesn't end up like that again.

Cheers,
Dan
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Old 04-10-2013, 23:58   #7
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Re: Penta MD11C cooling question

It is nice to hear when something works out well. ____Grant.
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