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  Topic Review (Newest First)
07-21-2007 08:38 AM
Originally Posted by T37Chef View Post
I'm not a trained mechanic either, but it has always been my understanding you should go 50/50, are you going 100% because its "diesel" coolant?
I went 100% because it's the same coolant I put in there last fall, just before I winterized the engine raw water circuit, A/C and head with pink "plumber's" antifreeze. My boat was out on a peninsula in a cradle exposed directly to winter winds...basically, I didn't want to screw around with 50/50 mixes if the temperature got to -25C, which it didn't (although an 80 knot gust blew over five boats where I was).

If there's a case to be made for going 50/50 in a cooling circuit, I'd like to hear it. It's not like a jug of coolant is particularly expensive.
07-20-2007 10:49 PM
Repair Manual


You really should get a copy of the service manual. It will have answers to all your questions.

I have the manual for the Universal M25 engine. For coolant it states 'use antifreeze.' Any automotive type coolant will be fine.

If you don't know when the coolant was last changed, you might as well drain it and change it now. There should be a drain on the engine block. Let all the coolant out (please catch it in a pan for proper disposal). Then fill with 50 / 50 coolant and water (unless you buy the stuff that is pre-mixed. There will be a coolant bleed screw somewhere on the engine, you need to find it.

Lastly, do you have an engine heated hot water heater? If so, bleeding all the air out can be a little complicated so make sure you do a thorough job. You will have to check the overflow tank a few times to make sure you have enough coolant added.

Good luck,
07-20-2007 09:32 PM
sailingdog T37Chef-

The sender or gauge could be mis-calibrated.

IIRC, most anti-freeze/coolant solutions have better heat absorbtion capacity and higher boiling, lower freezing points when mixed 50/50.
07-20-2007 08:47 PM
Originally Posted by Valiente View Post
I use green "diesel coolant" at 100% strength.
I'm not a trained mechanic either, but it has always been my understanding you should go 50/50, are you going 100% because its "diesel" coolant?

I thought (maybe still do) I had a "running hot" issue, changed the coolant, the thermo, cleaned out the heat exchanger, changed hoses, etc. The gage still says 210. So I shot a infrared thermometer all over the motor, it didn't read anything over 170, even at the injectors...I felt much better and now think it is the just a faulty sender or gage???
07-20-2007 08:32 PM
bestfriend Hmmm. I always thought, what the hell, antifreeze is antifreeze. On the short term, thats probably right. Its made up mostly of ethyl glycol, with about 5 percent additives. Its that 5 percent that makes the difference as far as what kind of anti-corrosive properties the coolant will have. Different types break down at different rates and will protect against different corrosive factors. I bought a new Ford in '03 and took it to one of those speedy lube places one time. They told me that it needed new coolant and that the system was rusted and needed service. They didn't realize that Ford had switched to a different coolant that is orange, not green. Diesel coolants tend to be a different viscosity, and can have seals made from different materials and different parts altogether. While you may not be doing short term damage, in the long term, you probably are if you are using auto coolant. I would recommend using what the manufacturer says to use, or at least a high grade diesel automotive one.
Oh yeah, and use distilled water.
07-20-2007 07:10 PM
jrd22 Any heavy duty truck or bus type of coolant is OK, Fleetguard is one brand I can think of. Should be able to get it at any auto parts store. Pre-mixed is easiest. We run it in all our diesel trucks and equipment, as well as our Yanmar and Volvo boat engines. It should say that it is recommended for heavy duty diesel engines on the jug. No need to buy Yanmar, Volvo, etc brand coolant.
07-20-2007 06:30 PM
Cruisingdad Call the Florida (Mastry Engines)... look them up under They are the East COast Distributor for Yanmar-Catalina. I have dealt with them too. I forget the guys name there... I think it is Bob??? But anyways, very helpful there too. You will not speak to them until Monday, obviously, but a lot better than Thursday.

- CD
07-20-2007 05:55 PM
labatt CD - Thanks for the reference... just tried them and Eddie isn't around until Thursday and nobody else was available at the moment... I'll keep doing my Internet searches
07-20-2007 05:36 PM
Cruisingdad Labatt,

Call Boatswain in California. Their number is: (949) 642-6800. THey are a Yanmar distributor. VERY NICE and helpful. I have dealt with them on many Catalina related issues. Ask for Eddy. He knows his stuff.

Get the straight and right answers directly from them. If you call them right now you should be able to reach them.

- CD
07-20-2007 05:29 PM
Valiente I just had this problem. It was a slowly leaking "rad" cap atop the heat exchanger. It was rated at 14 PSI: I got the same sized one for nine bucks at an auto parts store rated at 16 PSI. I'm glad I did (see below).

I use green "diesel coolant" at 100% strength. I must be doing something right, because my V-belt snapped when I was puttering to and from the poop dock, I didn't notice and the non-circulating coolant got to 230 F without boiling over or otherwise exploding.

But I sure as hell now know why they call it an "expansion" tank.

There are drain plugs usually on the front of the heat exchanger and/or at low points on the block in the cooling circuit. I have the shop manual for my engine (Westerbeke W-52) and I must say I refer to the thing about twice a month just to get used to all the extra crap on a bigger diesel when compared to an Atomic's a hell of a lot more engine.
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