Raw water cooled diesel running hot/head clogged up

Noah · Post by **Noah** » Mon May 21, 2007 9:22 pm

My new to me boat came with a 30 year old Volvo MD11C that is raw water cooled. After 30 years it is finally over heating. I had planned to pull the engine and replace, but a couple of mechanics said these old Volvo's are great and I should tinker with it a bit to see what is wrong.

So I pulled the engine out of the boat yesterday, and brought it home on a trailer. I got it going on the trailer using a small fuel tank and a hose into a bucket to run the thing. After a while the rear cylinder (it only has 2) started to overheat. Using my infrared thermometer I could see that the front Cyl was running at 145, and the rear 185-95. I have replaced the thermostat and the impeller seems fine.

At this point I really only want to put a few more hours and dollars into this engine before I buy a new one. Still, it seems worth it to try some kind of flush through the system to clean it out. Who knows, it could be something small lodged in there...

So, what do folks use to flush out salt and rust deposits on an old engine?

Thanks,

Slow

Jason K · Post by **Jason K** » Mon May 21, 2007 10:02 pm

I used muriatic acid on my Atomic 4 with great success. However, be sure that's not too strong for that motor.

Post by **Tim** » Tue May 22, 2007 6:21 am

It sounds as if you're holding out on us. Clearly, you have successfully trucked your new boat home from Florida. And yet, I don't recall seeing any pictures...

I must have just missed them, I'm sure. ;<)

Seriously, I hope that pictures of this boat on a truck actually exist. That must be quite a sight!

Your mechanics are right: those old Volvos are bulletproof and do tend to run forever. This is too bad, since they are loud, rough, cranky, ugly, smelly, feature expensive replacement parts, and don't have much else going for them.

But they do run!

Robert The Gray · Post by **Robert The Gray** » Tue May 22, 2007 12:47 pm

I obtained this from Don Moyer's A4 site. I imagine it could be applicable to the Volvo.

"Don Moyer comments Acid flush

Note: This acid flush is most effective when used as a preventative maintenance measure every 3 or 5 years.

Mix 1/3 gallon of household muriatic acid (30% concentration) into a 5 gallon bucket of water. Draw the entire 5 gallons of acid solution into the engine through the inlet "T" fitting used for drawing in antifreeze when winterizing. For best results, thermostat should be removed and the by-pass or recirculating hose temporarily clamped off. All the acid solution will then be pumped through the block by running the engine. Stop the engine as soon as the bucket is empty.

Start the engine after letting the acid set in the water jackets for about 15 minutes and run it long enough to thoroughly flush out the acid."

I have also been told to remove the exhaust manifold, place it in a plastic tray, then pour "On & Off Hull and Bottom Cleaner" all over it. Wear goggles and gloves and long sleeve shirt. be ready to rinse it somewhere it wont kill the plants. The manifold should be then clean.

This was another good post on the Moyer site.

"We have a 1972 Columbia 30 with a RWC A4 that was rebuilt in 1997 and is now overheating when at cruising speed (1700). I recently did an acid flush (as per your manual), but the engine still overheats, though not as much as prior to the flush. During the flush, it took about 5 minutes to empty the acid bucket which would indicate blockages in the cooling passages (impeller and thermostat are fine). How do I go about manually cleaning the passages that I can access without removing and stripping the engine down to have everything chemically cleaned out? - Top

If I'm doing the math correctly, you're only able to pump one gallon per minute through your cooling system. In most cases, blockages of this magnitude are not the result of general clogging of cooling jackets, but rather serious localized restrictions within a fitting.

Since you're experiencing a restriction to total flow, I would remove the hose to the inlet of your thermostat housing (directly above the starter) and run the engine for a few seconds. If you have good flow there, reconnect the hose and remove the one from behind the manifold and run the engine for a few more seconds. If you have good flow there, reconnect the hose and remove the end of the hose that connects to the exhaust system and run the engine again. By this process, you should be able to identify the segment of your system that is blocked, and limit the fittings to check. - Updated: January 3, 2004

Hope this was helpful,

r

Noah · Post by **Noah** » Tue May 22, 2007 1:23 pm

Thanks everyone, this is great info! Hopefully tonight I will have a go at it with some Acid and see what I can break loose. Maybe it will be something easy and I stick the old engine back in...Maybe not...

Ceasar Choppy · Post by **Ceasar Choppy** » Tue May 22, 2007 1:37 pm

One other place to check is the raw water injection elbow into the exhaust... this area is missed a lot of the time. Although for your symptoms, with the one cylinder heating up, it doesn't sound like it would necessarily apply.

Noah · Post by **Noah** » Tue May 22, 2007 1:55 pm

Where do you get household muriatic acid?

Also, what will it do to an impeller pump? Should I use some other kind of pump instead?

Thanks,

Noah

Figment · Post by **Figment** » Tue May 22, 2007 2:52 pm

Muriatic acid is commonly used (in a 10% solution) to clean mortar slop from new brick work, and for masonry cleaning in general. The local building supply place should have it.

Though it's an acid and should be respected as such, it's fairly benign to plastics. (it comes in a plastic bottle)
It's the stuff they use in car wax info-mercials I'm pouring ACID on the hood of this car and you can see that it's having no affect whatsoever! now THAT'S the protection of Super-Shine 5000, folks!!! (cue applause)
Unless you happen to purchase some super strength solution, your impeller and hoses will survive unscathed.

You're going to replace them anyway, right?

Post by **Tim** » Tue May 22, 2007 4:00 pm

FWIW, On & Off cleaner is a (relatively) dilute mixture of hydrochloric, oxalic, and muriatic acids. It is an excellent whitener (for gelcoat, or yellowed boot tops) and wood brightener.

windrose · Post by **windrose** » Tue May 22, 2007 4:30 pm

Trash in the water jacket? Maybe somebody else put a new impeller in it and there is a peice of the old one lodged somewhere.... that would be my second stop after the acid wash. Leave the acid in 15 minutes or so, so it can really eat the crub out.... you are going to surprised at what comes out of it. Good luck.

Post by **Tim** » Tue May 22, 2007 5:10 pm

Figment wrote:It's the stuff they use in car wax info-mercials I'm pouring ACID on the hood of this car and you can see that it's having no affect whatsoever! now THAT'S the protection of Super-Shine 5000, folks!!! (cue applause)

Wait a minute. You're not suggesting that the claims in those info-mercials are exaggerated or (gasp) even downright untrue, are you?

Noah · Post by **Noah** » Thu May 24, 2007 9:46 pm

So I ran a bunch of 30% Muriatic Acid through the engine for a while tonight. Much more water now moves through the thing, and I dropped the rear cyl hot-spot temp to 175 from 195. Being raw water cooled it is supposed to run cooler than normal, and the other cyl was staying at 130.

This temp was at high-rpms with no load. Will temps go up considerably with load? I'm going to try one more acid flush, then start pulling the engine apart.

Noah · Post by **Noah** » Fri May 25, 2007 9:49 am

So I ran my big 3/4hp pump on a reverse cycle for 45 minutes this morning with a bit more success.

At high RPM with no load the rear cyl got up to 165, but no hotter. (This is with the thermostat removed. The other cyl hit 113...

What do you guys suppose I should be aiming for for a useful engine in my boat? Do I need to get it all the way down to 130, or is something higher ok?

The hot spot is in one very small area pretty far down the block, not up near the head.

Thanks,

Noah

Figment · Post by **Figment** » Fri May 25, 2007 10:00 am

I've no experience with Volvo engines, but unless this thing has some unique criteria, 130 is well below optimal running temperature. I suspect that when you put a load on that thing the forward cylinder will hit 185.

How does the acid solution look at the end of the treatment? Lots of scale and gunk, or fairly clean?
Are you getting the engine good and hot before you start the treatment?