• Welcome to this website/forum for people interested in the Morgan 38 Sailboat. Many of our members are 'owners' of Morgan 38s, but you don't need to be an owner to Register/Join.

Perkins overheating


Terence Thatcher
I seek advice about my 4-108 which has always been reliable. I changed out the impeller, as advised, after over a year's layup. When I started up, there was no water coming out of the exhaust. But the raw water pump was pushing water out of the outlet (I pulled the hose and checked. Then I pulled the hose off the exhaust elbow, and no water was making it out of the heat exchanger. I put a hand pump in the exchanger to elbow hose and pumped--and lo, water started flowing. Some sort of airlock, I thought. We made an 80 mile run at cruising speed (1900 rpm) and the engine seemed to be running a little warmer than usual, but not dangerously warm.
So, we started for the Columbia Bar, in choppy seas, with the engine working hard and the boat being thrown around. After about an hour, the engine overheated dangerously and we sailed back to a marina, running the engine, with no water exiting the exhaust, for only 5-6 minutes to get to a dock and tie up. Next day, I pulled the heat exchanger out. There was a piece of old zinc rattling around in it, perhaps big enough to plug an inlet or outlet (raw water inlet on bottom of exchanger, outlet on top.) Otherwise, water flowed easily thru the exchanger. I removed the old zinc piece, put things back together and the engine, including the cooling, ran just fine, with proper temperature, for 7 hours of cruising under power as a test.

We crossed the bar and started beating into 20-25 knot northwesterly, engine off. We sailed for 12 hours, mostly on the starboard tack, and got tossed around pretty good. We then shifted to port tack in reduced wind. Engine intake is on port side of boat. As the wind died, we turned on the engine. NO WATER FROM THE EXHAUST. I went below and checked the raw water strainer--its water level was low, perhaps below the outflow. That has never happened before. It will typically fill the minute the seacock opens. So, I went to the raw water pump and took off the inlet hose from the strainer to the pump, and, lo, water poured out. Hooked things back up, turned on the engine, and it ran like a charm for 32 hours.

I think the initial overheating was caused by a heat exchanger plugged by the zinc. But I have no proof. Could the pump be weak? (Rebuilt pump maybe 300 hours ago.) But I have no good explanation for the stainer not automatically filling offshore after a rough 12 hours and no explanation for why it then refilled. (It is below the water line.) I did notice the inlet fitting was a little loose, but it has never leaked before. Since the events, I have checked the seacock and all hoses and pipes for blockages or collapse. All are good. I am going to replace the raw water strainer (Raritan) with a Forespar model.

So, I think things are probably ok now. My son and first mate, however, wants me to hire a mechanic to check things out. But what will he or she check? The engine is running fine, with proper temp and water in the exhaust. But I admit the events were disconcerting. So, I seek comments, suggestions, or any other advice you all might give. It was a strange combination of events and ruined a planned cruise. Thanks.


Richard Kilroy
Have you ever cleaned the heat exchanger. There are products you can by using a separate pump to clean the heat exchanger. This could be your problem if it has never been cleaned there is an awful lot of build up over 40 years in those areas inside the heat exchanger. I have used a product that I got from the Local Yanmar supplier that I ran through the heat exchanger and collected large amounts of rust etc. and rust particles. This is run by a separate pump that you hook up to the heat exchanger Anyway I would check the complete circulation system including the water heater to make sure there is not blockage somewhere


Richard Kilroy
Also if you are still using that old Raritan plastic heat exchanger from Morgan you have been very lucky. I replaced mine with a groco many years ago


Dave Ahlers
Terry, I had Perko strainer. I made my own top and bottom cork gaskets because I didn't want to spend $30 for Perko's versions. Turns out Perko's were thicker and I couldn't hold a vacuum at the strainer with the thinner gaskets. Water flow would come and go. I burned up a $30 impeller. Sounds like you're losing suction if your cooling water supply comes and goes.

On the pump, the little wedge can wear out, and the cover (gasket) can leak, even if the impeller is new.

The Sendure heat exchanger is easy to clean if its off the boat.
A broken zinc would just fall into the engine closed loop (anti freeze) side of the and really wouldn't cause problems. Still plenty of surface area to cool the engine.
The raw water (strainer/impeller) circuit flows from one end to the other through the tubes. There are removable caps on either end. On the raw water impeller "in" side broken impeller blades and whatever gets past the strainer can accumulate on this side and restrict flow thru the tubes. Look there for debris/blockage if you're sure the strainer and pump/impeller are good. If you pull off a heat exchanger cap, be gentle as there are o rings that seal the cap to exchanger body.

Lastly, you've heard the term "rodding" a radiator? No better example than a heat exchanger. With both end caps off the heat exchanger you should be able to look right thru the tubes and see daylight. If not soak it vinegar, and get a brass rod (1/8" I think) and gently tap the crud out of the tubes.


Terence Thatcher
Thanks. My heat exchanger only has one end that comes off. Last time I remoived it few years ago, I had it cleaned at a radiator shop. Can I find a new exchanger somewhere?


James M. Cleary
I'm not familiar with the Perkins engine as Dana has a Yanmar. To clean out (rod out) the heat exchanger a 3/16" wooden dowel does the job without damaging the tubes. Another point of interest might be your exhaust elbow. When the elbow corrodes enough to restrict the flow of the salt water cooling water into the exhaust stream, you may experience an intermittent blockage in the flow. Another point may be an internal blockage in the salt water cooling system. On Dana the system was isolated and a solution of Barnacle Buster was circulated through for 4 hours. The crud that came out at the end when finished was amazing. Since then the engine bearly gets up to 160 degrees, even when running for many hours. This might not be a solution for you but it may be worth looking into



Terence Thatcher
Dave, my zinc is on the raw water side of the heat exchanger. Wanted to check before I made a categorical statement. And Jim, I checked yhe elbow--it is pristine. I don't remember replacing it, but it looks almost brand new inside.


Mark Pearson
Staff member
I'm sorry to hear about that, Terry!
So are you up north now, or did you return to Portland?

For those that don't know, the Columbia River Bar is a world-class nasty piece of water. Don't want to be messing around with engine problems there. So, of course engine problems happen there a lot. Boats get bashed around in the waves and often junk in the fuel tanks breaks loose and plugs the filters.

I wish I had some solution to your issue, Terry, but all of my "usual suspects" have been covered.