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Morning and I hope everyone had a wonderful Christmas!

I've been avoiding replacing the heat exchanger on my 86' B28 knowing ist an expensive item. This past summer I had a slow rising temperature on the port engine at higher speeds that would cool down when I brought the boat back to slow speed or even idle. Again, once I put the boat back on plane, the temperature would slowly rise once again.

I first checked the easier items such as water flow and thermostat/exchanger cap and then to more expensive items such as raw water impeller, followed by the exhaust manifold and elbows. Each time I changed an item I ran the boat with the same slow heating as high as 200F which is when I slowed the boat to idle and allowed time for the engines to cool.

Finally, I was told by a neighbor my heat exchanger could be the problem as "the walls can thin" causing inefficient transfer of the recirculating water. This can cause a slow temperature rise and ultimately leads to a slow overheat situation.

I checked inside the ends of my heat exchanger and I must say, the passages looked very clean so I was really not sure if this was the problem. After replacing the lesser expensive items I decided to finally buy a new heat exchanger. After I took the boat out for a sea trial, what do you know, the port engine is now staying cool and not overheating.

Here's my uncertainty....the water temperature is now 59F here in Florida vs the 80F it was at when I initially started changing parts....

My question is, could the overheating be repaired with the installation of the new heat exchanger or could is it simply be the cooler Gulf water temperature and my issue will return as soon as the water temperature rises in the summer??

I look forward to everyone's input.

G.

G, you don't say what engine you have but your symptoms mimicked exactly an issue I had with my Yanmars years ago. In my case scale buildup in the heat exchangers limited water flow. I removed them and had them descaled, problem solved. In fact they are scheduled to come off again this winter for PM service after 5 years. My guess is you had the same issue but it was not visible to you. The new heat exchanger should resolve your problem. I've never heard of "thin walls" restricting heat exchange. Probably that opinion is worth what you paid your neighbor for it.

Yes, Im sorry. I have the twin Mercruiser 350' 260 MIE Engines. I was really anticipated seeing a scaleing issue when I took the end caps off and when I didn't I was wondering if I just wasted money on the new Heat Exchanger.

It seem to me that a change in water temperature would not like solve the slow over heating issue.

Higher seawater temp should not cause a steady rise in engine temp--just at best a slightly higher operating temp. I have the same basic engines on the east coast, and sea temps run from about 70 this time of year to 90 in the summer. My engines run 10 degrees hotter in summer than in winter. IMHO the HE's on these engines are just marginally sized for the cooling required--it doesn't take much scale to effect how well they work.
By the way, if you need another HE (when one goes the other is usually not far behind) check out Lenco--high quality product at decent prices.

It may have been a clog in the old heat exchanger. If you still have it, try plugging up the ends and get some barnacle buster and soak it following the instructions. That will dissolve any scale build up.

This past summer I just pulled my cummins heart exchangers and I ran a rod very carefully thru each opening and then flushed it with water. That solved my problem. Between the sea water and the zincs scale does build up in them and is normally visable.

I have never heard the Thin wall theory. I don't think that was the problem. If I were you, I would also check the transmission coolers.

Your neighbor may be half right, perhaps he meant a thin wall of scale developed on the heat ex-changer. I just read recently that scale is an absolutely fantastic insulator where it does not take much to hamper the exchange of heat. I'd rod, descale, pressure test, buy new gaskets and keep the old exchanger as a spare. To descale, barnacle buster, Home Depots muratic acid or bring to your local radiator shop and have "boiled out" and checked.

Yes going from hot water to cooler water will change your running temperature...but only by a few degrees and hold steady.

I'm with Carl. Just take it to a local radiator shop. If they're near the water, they've done marine heat exchangers. That way you know where you are on descaling and pressure testing.

You guys still have radiator shops near you. I thought they were a dying breed. All the ones around by me are long gone.

Tony Meola wrote: ↑Dec 29th, '20, 21:43 You guys still have radiator shops near you. I thought they were a dying breed. All the ones around by me are long gone.

They are a dying breed! I have a local guy and I have brought 2 radiators and a fuel tank for repair in the last year or two. Did not even want to touch them. Only wants to sell new stuff. I remember yrs ago bringing some beat up units and the old timers would re-core and solder em up and good as new...

I am like, what do I need to come to you if your just gonna order it for me on the web... I can do that myself and save money. I really try to support businesses like them but they are getting to the point they dont want to do the work.

BTW my example above were all parts from classic American made cars and the parts were not junk either...

Anyway, those heat exchangers would prob be ok if they were boiled out so DO NOT THROW them away.

Frank

My father was mechanic and he had a shop. I remember back in 70's the shops started calling us telling us they radiators we sent them were no good, and they would have to send us a new one. After about 10 in a row, my father had a long discussion with the guy and told him flat out he was pulling a fast one.

Found another shop, but now they are all doing it. But you are right, just buy it online.

Leco makes good stuff if you really have to replace them I still have the original 1966's on my boat.