New Cooling System on Perkins 4.236

16 Jun

This upgrade is common to all older Perkins diesels (the Perkins 4.108 is probably the most common Perkins found on boats). Bowman, the company that made the marinizing equipment for Perkins, has re-engineered things over the years, so that instead of having a combination header tank and heat exchanger on one part of the engine, and a water jacketed exhaust on another, they combine it all into a combination header tank/heat exchanger/exhaust manifold.

These engines were originally fitted with oil coolers. Now in some cases they say you can do away with the oil cooler unless your engine is run very hard. Since mine chugs away at about 1400 RPM cruising speed, I did away with the oil cooler.

At 50 years old, my old header tank was disintegrating (one surveyor took a very dim view of this), as was the heat exchanger stack, so that the whole business relied on a lot of polysulfide sealant and JB Weld. The old oil cooler failed spectacularly about five years ago, both blasting hot oil all around the engine room and filling the crank case with sea water. This is why one should always carry several oil change’s worth of oil at all times.

The first hurdle, and the only real engineering/fabrication part of the job is to modify the intake. If you look at the picture above, at the top of the picture you’ll see the air intake duct sticking out over the exhaust manifold. This would not do, as the new part would attach right there. The intake duct must be cut off and moved somewhere else. There are several ways to skin a cat, but I decided I wanted to keep my intake duct right in the middle, the way Perkins engineered it, but sticking up instead of out to one side.

I went off to my normal machinist/metal fabricator guy, to find a sign in his window saying he wasn’t taking any new work and would be closing up shop. I tried another place nearby, stood in the middle of his shop leaving him a voice mail, and never heard back. Found another metal fabrication place that was backed up four months. Left it at one place: They said they’d get it done the next week, didn’t, didn’t even bother to call me, then took off on vacation. I want back ready for battle, found the doors wide open, nobody home, and my parts sitting right where I’d left them two weeks before. I took my parts and my card and took my business across town. Is this telling me something? Should I be learning to weld? Is it just a Bay Area thing, or is it getting hard to find good tradesmen in this world?

At the second or third stage in this frustration I decided I’d go at it alone as much as I could, leaving only the welding to be done by a pro. The first step was to cut off the intake duct with a hack saw, which was satisfying and straightforward:

Then I went to and ordered a few pieces of stock, some aluminum tube to make the new duct, and some aluminum plate to cover the hole where the old duct had been. I used a 2-1/4-inch hole saw to drill down into the intake, making a home for the new duct. After a fair amount of cutting, sawing, and filing I had my pieces finished and ready for the welder:




Here are the old, tired bits that went away:

On top is the old exhaust manifold, which broke when I removed it. It was raw water cooled. The exhaust manifold on the new bit is fresh water cooled. Methinks this is a change for the better.

Here is the new bit, painted and ready for action:


There were many other little bits and bobs to source, customize, and fit. I had a brand new spare water pump, so I installed that while I was at it, replaced the transmission cooler for the same reasons as the heat exchanger, repainted where I could, and replaced all the engine hoses, as they were getting on twenty years. And I got one of those K and N washable air filters, since that’s what all the kids seem to be getting these days:


So far very happy with the modification. It did away with about fifty pounds of ancillary crap on the engine. Seriously, I’ve got a giant box of stuff, which I can barely lift, which is no longer needed, and this doesn’t even include the old header tank or exhaust manifold. And I’ve now got about another foot of space between the front side of the engine and the engine room bulkhead, which is great because the core of my electrical system is on this bulkhead.

The only problem is that she seems to run too cool. My wife asked, “Isn’t that good? You installed a new cooling system and now it runs really cool?” Excellent logic, but not exactly right. There’s a right temperature, which for Perkins is something like 160-180F on the cooling water. Mine seems to be barely tipping the gauge at about 120F. So now it’s off on a bay cruise with digital thermometer in hand to figure out if it’s an instrumentation problem or if she’s really running cool. Yes, I bought a new thermostat in case that’s all it is.

This article was syndicated from The Adventures of the Vessel Condesa


  1. Clark Beek

    Hi Nick,

    Sounds sweet. So you got the double cooler for your transmission, with one loop that cools the transmission fluid and the other the cools the engine oil?

  2. Nick

    Hi Clark,

    Got it all together, and the engine is running nicely. Ended up getting my air intake filter cut off and welded to the top, then put a K&N on the flange. Had to buy a new thermostat housing and a lot of hose. I went with the double cooler, but I run the engine for days sometimes. Thanks for the article to help get me going and I hope the next person that reads it is helped by the comments.


  3. Clark Beek

    Hi Nick, Exactly. I bought a new Bowman single cooler with the right sized orifices to fit my engine. Another little annoyance I came across is that to get rid of the oil cooler I to get rid of a fitting on the side of the engine, where both the oil filter and the oil cooler hoses attached. With this fitting the oil filter was mounted fore and aft, and with the new fitting it points down, and doesn’t clear the floor of my engine room. I had to grind away a little glass. Can’t seem to find a replacement fitting, with or without oil cooler hose fittings, but it works okay for now. Someday I might make the fitting custom.

  4. Nick

    Gotcha. I didn’t buy the kit, but I was able to source the thermostat cover. What about when you removed the oil cooler? Did you instal a single cooler for the transmission?

    Thanks for the info,

  5. Clark Beek

    Hi Nick,

    I just used hose to get from the water pump to the heat exchanger, but I think I made a standoff to keep it from hitting the pulleys or belts. I had a custom exhaust elbow already, and was very happy that the bolt pattern on the new heat exchanger was the same, so it bolted on right in the same place.

  6. Nick

    Hi Clark,

    Great article, very useful. I’m in the middle of doing the same thing right now. Did you fabricate a pipe
    To go from raw water pump to bowman unit? Or did you just use a hose? Any other modifications you had to make? Custom exhaust elbow?

    Thanks for your time,
    Hope to hear back

  7. Jeff Clancy

    Thanks for the insight, I’m just about to change out the Water cooled exhaust manifolds on my 4236m engines and I’m still undecided about going with the stainless exhaust manifold or the bowman aftermarket combo. The combo sounds like the better way to go at this point. Had to pull out the JB Weld on the last outing, glad I had it with me.

  8. Karl Atkins

    Hi Clark
    I’ve just come across this old post. I am in the process of over hauling my engine and will be fitting the new bowman heat exchanger as my original unit had pretty much disintegrated.
    I would like to know more about the conversion like what modifications I will need to do, also if you have photos of these mods.
    I am undecided as to do away with the engine oil cooler or fit a new one as I do use the engine a fair but and normally close to max rpm. What was the recommendations from Perkins as to this.
    Many thanks

  9. Clark Beek

    Hi Eddie, I’m sure there is some variation, but on my engine, and most I’ve seen, there is a thermostat housing that sticks out of the front of the block, and the header tank bolts onto this housing, sandwiching the thermostat between the header tank and the housing. On the new configuration a custom-made elbow bolts onto the housing, sandwiching the thermostat the same way, but then a hose attaches to the elbow and connects to the new header tank, about a foot away. I can send you photos if you want. Cheers, Clark

  10. Eddie


    What did you do for the thermostat housing? It was incorporated into the old heading tank wasn’t it?

  11. Clark

    Hi John, I got mine from Lancing Marine ( in England. I liked that they could supply complete kits, which you’ll find on pages 12 and 13 of their price book. Mike was very knowledgeable and helpful. Trans Atlantic Diesel ( can also supply. I got the kit, plus the transmission cooler and a few other bits and bobs and it came to about $2000 with shipping. On my system raw water is now drawn through the sea strainer, then the transmission cooler, through the raw water pump, then over into the heat exchanger tube stack on the new combination unit, which cools both the fresh water circuit and the exhaust manifold. The exhaust manifold is part of the new unit, so fresh water is circulating around the exhaust manifold ducting within the header tank. From there it goes up to an anti-siphon loop and then gets injected into the wet exhaust. I’ve done away with my oil cooler, on advice from a few folks, and from Perkins themselves, since my engine turns at low RPMs, Cheers, Clark

  12. john

    Can you tell me where you got your new header tank / exhaust cooler, and how much it cost? I assume that your raw water now goes thru the oil cooler, shell and tube raw water hx, anti siphon loop, and then to the exhaust elbow thereby bypassing the exhaust manifold. thanks

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