Larger Heat Exchanger for Perkins 4-108

[Wainui]

I have been looking at replacing the 12" HE on my 4-108. Sen-dure products have a streched out unit designed for the 4-108 that is 18" long for $630. Part #9873. Now I have to see if I have room to fit it without carving up too much woodwork.

[SkiprJohn]

I've got an old Perkins heat exchanger that you can have for $150 plus shipping. It came off a fishing boat engine and is about that size. 3" diameter in the middle. I could send photos if you might be interested.

Can't guarantee it though. I just know the guys I got it from said it was working fine.

kind regards.

[Wainui]

Unfortunately I can't fit anything longer than 14", but they can design on that is 4" in diameter which Then you would go from 76 tubes with 4.1 square feet of surface area to 138 tubes with 7.5 square feet. I may go this route.

[SkiprJohn]

Good luck on your project. Getting those old Perkins to cool down sometimes is a combination of a lot of things. Boiling out the old exchanger, checking exhaust and pump vanes as well as not overpropping. I used to run mine at about 1800 and if I went up to 2200 or higher needed to keep an eye on the heat gauge.

[BozSail]

Wainul, please tell us what you finally come up with, because I have the same issue with my 4-108 running hot. Thanks.

[gjordan]

I had the same problem as Skiprjohn on a 4-154. !800 was fine, 2200 would last about 15 minutes before it over heated. It turned out to be rust and salt percipitation in the cylinder head from previous owner running it for a long time with the rubber pieces on the ends of the heat exchanger being faulty. A valve job by the next owner solved it(head was boiled out). There are special products out now for removing the built up salt crystals, and the rust in cooling passages. I dont know of brand names, but they sometimes work and are worth trying before you go to the expense of a bigger cooler, or an even more expensive partial rebuild. I believe these products are different than regular radiator cleaner since they have to deal with salt. I assume you have checked all of the regular things, impellers, pumps, blockage in the mixing elbow ,or anywhere else in the exhaust system? Try the simple solution first, and if that doesnt work, go for the higher dollar fix. _____Good Luck with it._____Grant.

[Cheechako]

The 4-108 overheating discussion is wierd to me. Interesting to know. My 4-108 was pushing a 44 ft heavy cruisier. and did it very well in all sea conditions. never overheated even marginally. It had a heat exchanger on the port side of the engine that had a rubber cap like fitting on each end. My memory is fading but I think it was a Bowman heat exchanger. Might be something to keep your eyes open for,, on some old engine being sold....

[Stu Jackson]

My experience is that I recommend that folks remove their HXs on a regular basis. In most (but not all) cases, it is rarely the tubes that are an issue since the water is designed to move more rapidly through the small tubes, but rather is salt precipitation on one of the larger inlet ports where the raw water meets the heat of the exhaust liquid. Every year I find I have to bang off a pile of salt buildup.

I agree, the Sendure guys are great. They can make up any tube length and arrangement, so if you can't find one with the length that suits, ask them to make up one with more tubes.

Good Guys at SENDURE & Heat Exchanger Source & Flix

Good luck.

[Cheechako]

Here's the type I had... is this what you have? It pushed my 44 footer through PNW currents with a big Max prop at 8.5 knots hull speed.... no issues.... is it possible your exhaust is undersized? I know the 4-107's had a smaller unit, maybe some of the earlier 108's also...?

[Wainui]

My engine has just been redone and the HE cleaned with acid so no salt build up. I re pitched my prop so I can now get 3,000 rpm in gear. It is when the RPM gets over 2,600 that it starts to overheat (195). I am going to measure to see if I can fit the 4" x 12" HE. Sundure do not think that the 4-236 HE would offer that much more cooling than the stock 4-108 unit. This is the 12" x 3" unit that I have.

[gjordan]

What temperature does your manual say that the engine should run at? 195 degrees doesnt sound like being over heated at all. What temp thermostat do you have in your engine? If your temp keeps rising above 195 you have an issue, but if it steadies up at 195 you might not have a problem at all. Good Luck_____Grant.

[Stu Jackson]

Good point. There are 180 and 160 thermostats.

[lexowgrant]

did the larger diameter heat exchanger work

[Wainui]

I never got around to changing up to a larger unit.
I get 2600 rpms at 180 deg, anymore I overheat.
Sendure is a company that can make a 4" unit that will offer much more cooling. I may go that route.

[BozSail]

Wainui... I think if you run the Perkins 4.108 past 2600 rpms on any regular basis, you may have deeper issues.

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