2 inch heat exchanger

[jibes138]

I went out for a motor up the ICW on Sunday to have the boat hauled for a bottom job and assorted maintenance. The motor seemed to be running hotter than normal. I don't have a tachometer but I'd guess boat speed was about 4 to 5 knots. Motor usually runs around 160 degrees and very steady. This trip it was around 180 degrees and if I tried to go faster it would creep higher. The water in the creek is very warm now probably 85 degrees or more. Is the water temp alone enough to cause the higher operating temp or should I bite the bullet and do the 3" heat exchanger upgrade? I had good water flow through the exhaust and cleaned out the heat exchanger late last year. I hate to replace a part that is still in good working condition but would like to keep the temp at 160.

 

[Davidasailor26]

Jibes,

Assuming your engine is fresh water cooled, 180 is not an unreasonable temperature. A quick Google search indicates that the spec operating temperature for a Universal M-25 is 165 to 195 (http://www.marinedieseldirect.com/universal/200157/universal-owners-manual-m25-specifications.html). Running diesels too cool is (according to at least some claims) not a good thing either.

 

[jibes138]

good info, thank you. I guess it comes down to monitoring changes in performance. this motor has always run right at 160 to 165 for the 18 years I've owned it. to see it go higher started getting me nervous but I don't usually motor in 85 degree water. the delta T will certainly have some effect on motor operating temp I just wasn't sure if going higher than 180 was safe. sounds like it is OK. temp was definitely increasing with changing RPM's so the cooling system seems a little under capacity. with higher RPM's increased cooling water flow should keep the temp pretty constant. all the newer M25's have a 3" heat exchanger and it is a recommended upgrade, so I'll likely pull out the wallet and go for it. I hate the thought of crawling around in there when it is 100 degrees out though to change it out. :>)

 

[Maine Sail]

Dave,

The simple answer is if you have the 160F stat, which the M-25's of that vintage do, then 180 is too hot. Sure the engine can run at 180F but it is simply telling you the cooling capacity is not there. I can't believe there are actually M-25's out there still going with a 2" exchanger. Definitely go to the 3"!

You don't need to get it through Westerbeke there are plenty of cross referenced 3" HX's made for that motor for about half the price. You will likely want to custom fabricate your mount for it but it is not too difficult. You can even hodge-podge the 2" bracket and make it work pretty well.

The next time you are racing to beat that front and lightning storm you'll be happy your engine isn't pushing 220F....

 

[SailingCal21]

Dave,

If it historically ran at 160 (IMHO does seem like a low operation temperature, good for you) and now its running higher, I'd suggest that you to a thorough inspection and cleaning of the tubes and see where that gets you. Sometimes Karma would take several seasons to have cooling based heat exchanger issues and sometimes only one season. I always attributed it to the local water chemistry causing excessive scaling, of course I would occasionally fish out bits of zinc and other crud even though I have a strainer on the raw water intake. I use a coat hanger wire with one end flattened with a bit of a twist to make an auger to rod out the tubes.

Keep in touch with the local yards, I managed to find a 3" heat exchanger from an engine refit for $100. As Mainsail pointed out the 2" bracket can be made to work. I used a thick piece of rubber to isolate the exchanger from the bracket. So far it's working quite well.

Karma's original thermostat was a 180, PO replaced it with a 170. I've got the older 5424 which is spec'ed for 170-185, I've often wondered if it would be better to run the temp on the high side instead of the low side?

 

[Tom Potter]

Jibes,

I went through the same ordeal last summer. Temps rising and falling with RPMs. Discovered several tubes stopped up and a couple partially stopped up in the heat exchanger. Sounds like you have a restriction somewhere as well. Could be the heat exchanger or some growth (barnacles) on your intake strainer on the hull.

 

[Maine Sail]

Dave,

If it historically ran at 160 (IMHO does seem like a low operation temperature, good for you) and now its running higher, I'd suggest that you to a thorough inspection and cleaning of the tubes and see where that gets you.

The M-25's (the M-25, M-25XP, M-25XP-A & M-25XP-B) all shipped with a 160F t-stat. The t-stat part number is 301358 for the earlier engines like Jibe's.

If the engine is running hotter than 160f then the cooling system is not doing its job. Most all of these engines have been converted to a 3" HX due to inadequate cooling performance because the 2" HX had a very tough time keeping up...

 

[Stu Jackson]

http://c34.org/bbs/index.php/topic,6920.0.html

 

[jibes138]

Yeah last year I pulled the HX and used a wire to clean out the tubes, flushed out the hoses, snaked out all little pieces of zinc, etc. I have found that the fitting to the exhaust elbow tends to clog up with solidified salt, it is a right angle fitting and the water seems to sit and then dry when I don't use the boat for a while. I'm tempted to put a flushing line with a valve so I can flush it with fresh water after each use, like you do with an outboard. As previous projects have shown I'm a bit slow on the upgrades, just did the alternator bracket this year, and haven't done the wire harness yet either. Now that my new fuel tank is completed the harness and new HX is in order. I probably should have cleaned the HX at a radiator shop with acid but the manually cleaning seemed to do the trick for a while. I wonder if the salt is solidifying in the tubes also from sitting around for a while? I need to do a bottom job and wax the topsides then I'll get back into the mechanicals, as with all motors they seem to run a lot better when you use them all the time. Maybe I can recruit the boy scouts to take me on as a community service project for a merit badge and they can do some sanding and waxing? :>)

 

[SailingCal21]

Jibes,

Could be the heat exchanger or some growth (barnacles) on your intake strainer on the hull.

Yup, barnacles in the thru-hull, tis about the time of the summer when they start to get some good size to them.

 

[BarryL]

Hey,

My boat has the 3" HX and a 180 thermostat. The higher the thermostat the more efficient the engine is. With the 3" HX I can run at 80% max RPM all day and the gauge never goes above 180.

 

[jibes138]

If the HX capacity is adequate the thermostat should regulate the temperature at equilibrium at the set point of the thermostat. Basically it will modulate to control the temp at the desired point. Since mine is going higher it is either insufficient HX cooling capacity or insufficient raw water flow to remove the heat at a fast enough rate. I thought I had pretty good water flow but didn't actually measure it as I was under way. I think the 2" probably does the job when everything is in tip top shape but has no reserve capacity to allow for partial restrictions in water flow, or heat transfer changes due to scaling. Since removing and cleaning the system is a PITA I think it best to put in the upgrade to get a bit of reserve capacity and reduce the frequency of removal and cleaning. I dove on the boat a month ago to clean the hull and the intake seemed clean but critters might be growing inside the strainer. I live in barnacle and oyster heaven so I won't be surprised to see some restriction. Had to leave town for a while, I'll update this thread when I get back and go through the system. Thanks all for the inputs.

For another thought why have the heat exchanger mounted on the engine? Why not have a nice heat exchanger installed where it is easy to service like right next to the water heater in the cockpit locker. It is just a bunch of hoses so it theoretically can be located anywhere and doesn't have to be this Universal style design. I wonder if a water heater would do the job by circulating the raw water through the fresh water circuit and the engine coolant through the system already in use? The water heater is a heat exchanger and might have capacity to cool the engine? You could have a water heater for the fresh water in the boat and a second one for the engine cooling. Maybe a better way to skin the cat?

Maybe Maine Sail can design a new "Universal" remotely located heat exchanger with simple cleanout capability that he can license for production and sell as an aftermarket device and make millions on it? We would all induct him into the SBO hall of fame!! The following is an example (no affiliation with this company, just an example of an alternative possibility):

Brazed-Plate Liquid-to-Liquid Heat Exchangers for Maximum Performance

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[Maine Sail]

Jibes,

The "plate" HX's have been around for a looooong time. I used to rep one back in the early 90's. They work well and from a manufacturing stand point, simply add more plates to increase transfer capacity.

However in a marine RW system they would be the last product I would use. The passage ways are very, very small and even in hydronic systems they are prone to performance degradation if the boiler water becomes dirty and is not treated. There are also many low quality brands of these out there so one needs to be careful who they buy from. For swimming pools/spas 316SS or Titanium versions are used. People try to use less expensive versions but they last months vs, years in that applications. We sold them to heat pools, air handlers, hot water storage tanks, process tubs etc.. and if not careful with how they were plumbed, pre filter etc.., they could pug up in those installs too.

There is no need for it to physically be on the engine but you will need to extend hoses, account for hose chafe, create a mount and have the physical space to re-locate it... It can also make it more difficult to bleed the AF side if it is installed above the cap on the manifold and measures are not taken to account for this........

 

[Stam22]

I have an O'Day 34, had the same problem, took the heat exchanger to an old fashioned radiator shop. The boiled or steamed it, or whatever they used to do to radiators before they started making them out of plastic. When I got it back, it was clean as a whistle so I had to repaint it, now the temp never goes over 165.