Heat goes up and down on Volvo Penta

[michaeltayar]

Hi there,

I have a Volvo Penta MD7a that starts and runs great but the temperature gauge goes all the way to the red, holds for 2-3 seconds, then goes down to green, stays in green for a few seconds than up in the red! The gauge keeps going up and down specially where the revs are up.
I used a handheld temperature gun on the engine and it reads from 180 to 220 depending where the gun is aimed.
The impeller, sender and thermostat are all new.

Running out of ideas. Can anyone help?

Thanks,
Michael

[Don C L]

Ahhhh the MD7A.... well, was it ever rebuilt? How does the water seem to be spitting out of the exhaust? I am guessing not too well. A good friend of mine with a Cheoy Lee just went through this. The symptoms you are speaking of came just before the needle finally pegged in the red and only came down as we slowed down. Pretty soon we were doing about 1 knot and it wouldn't come down and we shut it down. Since there was zero wind we relented and called for a tow. Those engines are good but old and raw water cooled, and a black gunk will build up in those over the years. An acid bath run through the cooling system MAY help some, but I hate to say it, but the best way to deal with it is to take the engine out and take it apart to clean out all the places gunk can build up. That's what we did and now it is running quite well. If the engine is running hotter than 145 sea water starts to build up even more sludge. And 220 is definitely too hot! That is probably not the post you wanted to hear, huh? Oh, and he spent something over $1000 on replacement parts in the rebuild. That didn't help.

[four winds]

Same symptoms as a friends md11c. Plus some steam out the exhaust.

Been surfing online today trying to help. So I read that the cycling temp issue is caused by blockage in the ports between the exhaust manifold and the head.

My friend is a hundred miles up the coast and doing a CLR flush of his engine. He just texted a few minutes ago and said the temp is stable now and not rising. But still has some steam.

[Don C L]

Always good to check the water intake too. I'd take the hose off the through-hull and make sure the line is clear going in. Then open up the through-hull and let the water come in. (A little in the bilge won't hurt, or catch it in a bowl or bucket. Have a big pipe cleaner ready to poke down in there. Make sure the valve and handle are ok too. My friend's valve was corroded enough to break half-way open too. Of course check the filter too. Hope it turns out to be something simple for you! How is access to the engine in your boat?

[michaeltayar]

Engine spitting out water pretty nicely and more as I give gas.

I did clean up some gunk and build up round the thermostat housing.

Somebody suggested an electrical issue!!

Access to the engine is very hard for a toddler. I'm 6.1!

Access to the water intake is difficult where the boat is (heard of an alligator around)


Sent from my iPhone using Cruisers Sailing Forum

[Don C L]

Not sure if you have seen these:
Volvo MD7A raw-water cooling flush - BoatBanter.com
http://boatdiesel.com/Forums/index.c...hread_ID=55519
http://www.cruisersforum.com/forums/...ng-144421.html
http://www.cruisersforum.com/forums/...d7a-17661.html

[rhoboat]

Check the intake strainer gasket and tubing. I had a faulty seal that gave the same symptoms until I replaced the gasket.

[Dartanyon]

I've got a MD-11C, also raw water cooled. My guess is, Four Winds hit it right, the water galleries around the cylinders have fouled. Salt gets in there, calcifies, and restricts the water flow. The temp going up and down is the water going in there, heating to boiling and then flashing to steam, allowing more water to go in.

I've had good luck with an external pump, and a bucket of CLR + water. Grab the hose coming out of the engine's water pump and the hose leading out to the wet exhaust, drop them in a bucket with the pump and cycle the solution through the cooling system. I've done it at the beginning of the last 2 seasons, with good success. I don't think this solution with last forever, but the gasket kit is terribly expensive, and the real solution is to get to the galleries and manually chip away at the deposits.

There are lots of posts around the usual site describing it in better detail.

[a64pilot]

CLR is not very aggressive, for AC units I and I believe most use diluted muratic acid, used in pools and cleaning concrete of course.
I think I'd try flushing it like it was an AC unit myself, but above 140 or so degrees, and your building deposits

[Valmika]

I had an issue like this on the westerbeke closed cooling system. Part if it turned out to be corrosion on the wire on the gauge itself.

[Dartanyon]

Originally Posted by a64pilot

CLR is not very aggressive, for AC units I and I believe most use diluted muratic acid, used in pools and cleaning concrete of course.
I think I'd try flushing it like it was an AC unit myself, but above 140 or so degrees, and your building deposits

True CLR is not very aggressive and there are certainly more aggressive chemicals to use, I was trying to go with the least potent that would get the job done. There are lots of copper bits on my engine, and I was trying to go as easy as I could on them, chemically speaking.

I have the gasket kit, and I was going to pull it all apart but maybe I'll try to muriatic acid first and see if I can use that time for sailing instead.

[a64pilot]

I don't think muratic is that bad on copper as many AC systems are of course full of copper too, but it might wreak havoc on aluminum, and certainly zinc.
Change your zincs after a flush with muratic as you may not have any zinc left

[Mojadito]

Be sure to check that you have bled the system of air, especially after a thermostat change. Volvos have a small bleeder valve, usually on top of the thermostat housing, but may be anywhere on top of the engine. With the engine running, just open the bleeder until clear water (or coolant if a heat exchanger system) comes out and it quits burping air. May not be the problem, but it is a cheap easy fix.

[Rex Delay]

My old Volvo did the same. Turned out in the end that the cooling intake hose was wrong and would collapse under suction causing exactly the same symptoms. Cheap and easy fix.

[Panama Dave]

Is the MD7 raw water cooled? If so, it is normal. We have a raw water cooled MD17C in a boat we bought 12 years ago. In a raw water cooled engine you will never achieve a stable temperature. The engine heats up till the thermostat opens, then the cold sea water drops the temperature drastically. Then it repeats. We have crossed the Gulf of Mex 4 times. we've sailed from Texas to the Bahamas and from Texas to Honduras. Our engine has done this consistently with no problems. Make sure your system is clean and all parts are new then establish what "normal" is.