Engine overheat; troubleshooting?

[Steve_M]

My engine overheated on the way back to the mooring last night. It's an MD7a with fresh-water cooling. Water stopped coming out of the exhaust, so can I assume that the first thing to check would be the raw water pump on the aft-facing side of the engine?

I know this is a newbie question, but I've never owned a diesel before...

[Maine_Buzzard]

Lots of suspects here-

When was the impeller changed? if more than two years, start there. How is the freshwater pump installed? Hung on the camshaft/starter gear drive at the forward end? Just wanted to check.

Start at the intake strainer. Did a cover plate get painted over a few weeks ago? The holes get smaller and smaller with each coat. Dive and take a small screwdriver to clean the holes out. Do you have a strainer inboard? Clean the basket there, after closing the seacock. Was the seacock open? The thermostat is not a big suspect here, since the water stopped flowing... You have a heat exchanger cylinder on the inside of the engine compartment, with a cap for the coolant at a high point? Open the inspection port on one end to look at the cooling tubes on the raw water side. Any plugging? It probably needs a new zinc there while you are opening it up.

Take all of the rubber hoses off on the raw water side and look for plugging at the fittings to the hoses.

Check the fresh water side for coolant too. Again, not the usual problem when you have no water in the exhaust.

Take pictures!

[Stan W.]

Steve, on CD 28s with fresh-water cooling the raw water pump is actually the belt-driven pump on the front. And yes, that is the first thing you should check (assuming the raw water intake seacock is open).

[Steve_M]

Steve, on CD 28s with fresh-water cooling the raw water pump is actually the belt-driven pump on the front. And yes, that is the first thing you should check (assuming the raw water intake seacock is open).

That's exactly what it was; the impeller on the pump mounted on the front of the engine needed to be replaced (and I had one on-board, too). The flow of water from the exhaust is substantially healthier than it was the first time I fired the engine up.

Start at the intake strainer. Did a cover plate get painted over a few weeks ago? The holes get smaller and smaller with each coat.

That's a good piece of advice. The night before launch I happened to notice that the cover plate had half of the holes painted over, so I spent some quality time cleaning them out that night.

[Ken Cave]

If you have a Volvo engine (MD7A) you probably have a Johnson Pump that is in need of replacement parts that should be carried onboard such as impellers. There is a great site in Seattle called Marelco
that has a store at 3900 3rd. Avenue NW, Suite 2. Bill Tibbits is the owner and has all the parts
available for Johnson pumps at about the third of the cost from a Volvo dealer. He is also a wealth of information on pump repairs, etc.

His number is 206 545 4224. Bill's email address is www.johnsonmarinepumps.com.

Hope this helps

Ken Cave
CD 28 #227
LaConner, WA

[Stan W.]

The coolant pump (running off the back of the fuel injection pump) is definitely a Johnson. The raw water pump may or may not be a Johnson. Mine is, but I have heard of others with Jabscos, etc. Johnson is still a major supplier of pumps and any marine chandlery can get parts for them.

[Steve_M]

I can confirm that on the Wolf the raw water pump is a Jabsco.

[gates_cliff]

Have Westerbeke 13, was going out today and overheat alarm went off, close enough to dock turned around and back to slip. Shut the engine down and removed water pump cover expecting to need to replace the impeller. Looked ok, so put cover back on. However, there was a great deal of water that drained when I took the cover off. I don't recall that being an issue the last time I replaced it, so wondering if that might suggest a clogged hose.

I waited long enough for engine to cool down, checked oil to be sure that wasn't low and it was ok. Restarted the engine, water coming out exhaust as expected, let it run for about 15 minutes then alarm goes off again, and temp gauge is registering hot.

Not sure what to do next.

[Joe CD MS 300]

Is water still being pumped out when it overheats? Impellers can appear to be good but can sometimes spin on their shaft. I had that problem for years. It could work on start up but then stop when warmed up.

Since or if the sea water appears to be flowing through the heat exchanger system OK (assuming that is the type of system you have) even when overheating did you check the engine coolant? Do you have an overflow tank?

I always forget which part of the cooing system is called fresh water vs raw water.

[Nebe]

If your boat is in a slip, bring a small shop vac on board and attach the hose of the vacuum to the raw water hose down stream of the impeller. let her rip while someone is watching your transom for any signs of blockage to come blasting out.

I am not sure i would attempt this technique to the other side of the impeller, but its easy enough to see if you have clear water flow by just disconnecting the hose from the impeller housing while the seacock is closed, then open it slowly.

[gates_cliff]

Thanks for the responses. I'm at work and generally can't get over to my boat during the week. there's a great mechanic that has a shop at the marina where I am, so I'll ask him to check it.

By the way, if you are in the Deale or Galesville, MD area I highly recommend this guy and his brother, Marine Engines Unlimited. It's two brothers and they do all the work. Very reasonable and don't do anything unless it's really needed. They do work further afield from Galesville, not sure how far they go though.