Slate-like flecks keep clogging my Thermostat!

[grania]

Im wondering if anyone has had this problem! I have a Volvo Penta engine on my 9M CD, and I have a chronic but intermittent problem with overheating. Checked the impeller first, the water pump, etc. It turns out that when I removed the thermostat housing cover what I found inside was a little pile of black slate-like chips just clogging things up in there. I cleaned it as best I could and replaced the thermostat. It worked great...for about a day! Then it just starts over again-intermittent poor flow of water from the exhaust, the temp gage going up-but improving if I decrease the throttle-I've replaced the thermostat 3 times! Do I need to somehow flush the engine? Is this engine, which is 22 years old, doomed? Please help if you have advise! Much obliged, Aine

[Michael Abramson]

You probably have the same MD7A that is in my Intrepid. When you had the t-stat out, you removed the dome shaped cast iron housing. Did you also stick your finger into the exhaust manifold to see if it had an accumulation of the scale? Usually there is a lot just inside the exhaust manifold, and you can scrape and dig most of it out with a small tool.

On my engine, the exhaust manifold was badly scaled inside, so I removed it and soaked it in a muriatic acid solutions that cleaned out much of it. You still have to do prodding and scraping, some of the passages may be completely clogged. The manifold is held on with 4 bolts only, but of course you first have to remove the water hose to the mixing elbow and from the elbow to the muffler. I found all of the parts I needed to do the job on eBay for a fraction of the dealer price, but you need to have a parts list to know what numbers to look for. The main thing is the gasket between the manifold and cylinder head.

I would not replace the t-stat unless it shows sign of corrosion or other damage. You can test it at home in a pot of water on the stove and a cooking thermometer to verify it opens at the designated temp. I would however replace the little square section o-rings between the domed housing and the exhaust manifold when you do the job.

One other thing to check if you have poor pump output would be to verify you have good water flow through the water jacket of the transmission and on the the water pump. Remove the cover to the pump and then have an assistant open the engine seacock. If it comes flooding though the pump, you know there is no blockage.

[grania]

Your advise is more than appreciated! I do indeed have the same engine. And it sounds like the same problem, no doubt. Did this pretty much fix it or do you still find you need to remove the T housing and clean out? Also, you mentioned parts needed to remove and clean the mannifold-any chance you have that list lying around? I am very new as an engine mechanic-altho I have amazed even myself with what Ive learned as a boat owner of an old engine. It felt great when I thought Id fixed the problem the first time I found the shale, cleaned it and watched the water just gush like never before from the exhaust. It was a short-lived joy. Anyway-at least I am figuring it out-with your help!
Thanks much-Aine

[Oswego John]

Hi Aine,

Simple question. I'm curious to know if the chips are attracted to a magnet.

What do they appear to be made of? Can you tell if they are metallic, or maybe plastic, neoprene? Do they melt when heat is applied? Do they ignite?

Is there a chance that the black might be carbon? Did you try to scrape any of the black surface off, or is the entire chip black, through and through?

Curious,
O J

[Tony Batchelor]

When iron rusts it delaminates in platelets as you have found.
The worring thing is that once you start poking and scrapping rust from the parent metal you might find there is more rust than metal so don't be too keen to get stuck in.
Rust should be Non magnetic but in practice there is usually enough iron particals left to have a limited attraction.

On the same line anyone who has raw saltwater cooling will not doubt have wondered about rust within the engine.

Has anyone found a way to convert any of the MD series engines to fresh water cooling via a heat exchanger? I asked Volvo but they were only interested in supplying a new engine.

[Oswego John]

Hi Tony,

For years and years, long before small diesels were made available to boat owners, the poorer working class owners who couldn't afford marine engines used auto engines in their boats.

The first conversion I remember was my uncle had a four cylinder Ford Model A engine in his work boat, back in the 30s. When you think about it, a fresh water cooling system on a boat that sails in salt water is similar to an auto engine. They both have sealed cooling fluid systems that recycle the cooling fluid.

Many of the conversions used various forms of keel coolers, ranging in complexity from crude to complex. Most of the coolers I was aware of were homemade. It was basically a sealed tank that sea water was pumped in and then out of the wet exhaust. Inside of the cooling water tank was a coil or trombone shaped copper tubing in which engine block water was piped through with a second water pump. Some people used an early version of baseboard heating type fin tube. A popular type tubing that was used was like a Tago type immersion domestic hot water heating coil.

So, to answer your question, I feel that it's doable. I would think that a conversion could be installed, whether store bought or home made. You'd have to alter the plumbing some, and provide a power source to drive the additional water pump. Maybe iron out a few other wrinkles.

Go TNZ
O J

[Michael Abramson]

While I'm sure a purpose-designed or generic FWC system could be retrofitted to a MD7A or similar Volvo diesel, the issue to me is whether the almost 30 year old block and cylinder head would then stop the internal corrosion. I would like to know if anyone using one of these old Volvos has ever had the block or head become porous from the corrosion of the waterways. Surely they can't last forever after a lifelong diet of salt water, and the anti-freeze solution of a FWC system is not going to add metal back.

I found the cast iron exhaust manifold of my MD7A had started to
convert from solid metal to a black carbon-like substance that had some integrity but could easily be gouged with a screwdriver. I used JB Weld (if I remember correctly) to build the deteriorated areas back up so that the t-stat housing and mounting surface could be then filed flat so the gasket would reseat. I had not heard of or witnessed of this kind of deterioration before.