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FAQ: Overheating - Heat Exchanger?

Overheating with 2" heat exchanger, can I install a 3 inch instead?

I am overheating with 2" heat exchanger

How much is the 3 inch heat exchanger and how difficult is it to change? Where can you get it?
Mike Crosa, mcrosa@mindspring.com

I think I paid something like $180. Canít remember exactly. Very easy to change. You have to fool with the mounting brackets but that is it. The hose connections are the same.

Mike: I bought mine from Torrenson Marine. Found them on the web: http://www.torresen.com/~torresen/universal/welcome.html. I called on the phone, they were fast, helpful and expensive. About $400.00 for the exchanger. It fit right on the same mounts as the old one. It has been flawless. The engine temp has routinely been 160 instead of 185-200.
Thomas M. Barba, tbarba@email.msn.com

I finally broke down and bought a 3" heat exchanger. You have a lot more margin in the system plus you can take off both ends of the heat exchanger for cleaning out the zinc pieces.

Hi Stu, I get all my stuff from, can't remember the name but their number is 707.426.6670. They are great. The heat exchanger is expensive though, about $350.00 but the installation is straight forward. You will need a piece of 3" steel pipe to reshape the bracket and that's tough to find. I have a piece if you can arrange a pick up. I took the bracket off the engine to reshape it. Simple job. You mares well change the hoses while you're at it.
The rep said the 2 incher is marginal but still ok for our cold water. but for the extra $50.00 or so I went for the 3 incher.
David, C34 #247

I fought overheating on my 1986 Catalina with 2" heat exchanger for a long Time, like 5 years. I live in NW florida in warm water. I agree that the 2" is marginal (so does Catalina since they switched to the 3".) However, if everything is tip top the 2" will keep up. If you are going above thermostat temp under any conditions, full throttle for example, you have at least a minor problem Start with the sea water system: Check for grass/barnacles in intake and filter, new impellor in sea water pump (old can look good but be stiff and not sealing well), broken impeller blade from an old impeller problem somewhere down stream. Take out heat exchanger and shake it. If it rattles you have old tips of pencil zincs inside. (The dissolve in the middle and the tips stay in there.) They will plug the cores and are a major cause of overheating problems. Take exchanger to radiator shop and have it boiled out. That may not do it. If you pound and shake long enough you can get them out of the pencil zinc insertion hole. Check for bent or pinched hoses impeding water flow. Check for carbon buildup where the sea water dumps back into the exhaust pipe partially blocking the water flow. On the fresh water side, if you have air in the system, you will get inefficient flow and pump cavitation. Look at the check valve between the overflow tank and the plumbing to the hot water heater. (located in cockpit lazerette) This valve is not made for antifreeze. I recommend replumbing the rubegold burg plumbing valve at the rear of the engine used to control amount of heating going to the hot water heater. It is a major source of cavitation and air. Replumb the hot water heater to the thermostat bypass fittings (short hose between the fresh water pump and the thermostat housing) [That's the way the new engines are plumbed] Try a new thermostat. It may be stuck closed. (take it out and see what happens) Your problem may be one or several of these items each contributing a minor amount of inefficiency PS. I finally broke down and bought a 3" heat exchanger. You have a lot more margin in the system plus you can take off both ends of the heat exchanger for cleaning out the zinc pieces.

Subj: Re: M25XP Heat Exchanger
While on the subject.....I noticed some rust around my exchanger where you put the anti-freeze in. Is this an indication of other cooling problems to come??? I have not had any cooling problems to date. Is this just a scrape and paint fix or should I look at other detail????
Clarence Mann,  cmann@14wfie.com (cmann)

Donít mean to get "preachy" (My wife accuses me of that) but just like in sailing where we use specialized terms like "halyard" or "sheet" instead of "rope", the proper terms lead to better communication. The "exchanger" is a rolling pin sized copper tube mounted just above the transmission at the stern of the engine. It wont rust. The item that the radiator cap and fill neck are attached to is probably called something like the "exhaust manifold water jacket". ( I haven't ever seen it individually named) It is part of the "maximizing" that Universal/Westerbeke do to the Kubota tractor engine. I believe that it is made out of cast iron which will rust. Anti freeze is very corrosive and will cause rusting. I believe that you do not have a major problem. Clean the spot up and spray paint it would be my advice.

I also have an engine with the 2" heat exchanger. I had a heating problem until I had the heat exchanger cleaned out. It used to run at 180 degrees, and eventually got to the point of getting to 200 degrees at maximum rpm. Now my temperature varies between 160 and 170 degrees. I am also using a 3 blade prop. I don't recall much difference in temperature when I switched from the 2 blade to the 3 blade (both Catalina recommended sizes.) I understand that there is the 3 inch heat exchanger available which would undoubtedly have more heat transfer ability. The only other thing I can think of that may make your situation different is warmer water that you sail in, or a problem with your thermostat. Also, if there is any restriction in your fresh water loop (or raw water loop), you will slow down the flow and have less heat transfer. Good luck.
Michael Dobrzensky,  MSD1@pge.com (Dobrzensky, Michael)

 Important: The opinions expressed here are those of the individual contributors to this page, and not those of the Catalina 34 National Association or Catalina Yachts, Inc. Additionally, this material has not been reviewed by Catalina Yachts, Inc. for technical accuracy. This page's maintainer cannot guarantee the accuracy of this information or the desirability of suggested modifications or upgrades. Please obtain assistance from a competent marine mechanic or boatyard prior to making any significant modifications to your vessel.   

Last modified by Phil Imhof, Wednesday, August 11, 2004 . Copyright © 2001 by Catalina 34 International Association.  All rights reserved.