MV34 75HP Engine Overheating

[ThomKat]

Anyone experiencing overheating on their MV34 with the 75hp engines, the port engine in particular?

We've seen it on ThomKat (MV3475) and are presently trying to determine the cause. In our case, the situation manifested itself when we tried to run at full throttle. After about 10 minutes, temps on the port engine approached 100C and might have exceeded that had I not slowed down. As soon as I dropped the rpm under about 3500, the temps returned to (close to) normal.

If you've seen this, please provide some particulars, i.e., how were you loaded, what rpm were you turning at full throttle, what was the air temperature, etc., etc.... If you wish, you may contact me directly at a-castle@earthlink.net.

Thanks!! Tom

[duetto]

hi tom,

we've seen elevated temps on our starboard engine when we push at 3400 for hours on end. however, it climbs to 90 and stays there. we travel with full tanks (fuel & water), 10' dinghy w/15 yamaha, and lots of stuff. we've lived aboard since oct. we just got back from bahamas. we made run from great guana to west end to ft pierce and averaged 14knts for the 200+ miles.

[Marleetet]

Deleted

[ThomKat]

Many thanks to Duetto and Marleetet for their replies. And thanks also to those who contacted me directly.

We haven't found a definitive answer yet but it appears that our heavy loading and an air leak in the raw water strainer combined to create the problem. We replaced the strainer and are modifying our propellers to see if depitching will allow us to get the engine rpms back up to the Yanmar recommended numbers without overheating. (Yep, a long run for a short slide....!) Initial results are encouraging but we still need to do a bit more testing before saying we've solved the problem.

Thanks again!!!

Tom
ThomKat MV3475

[duetto]

hi tom,

what diameter/pitch are you trying? when you're done testing, i for one, would really appreciate a speed to rpm plot and any other data that you can provide.

thanks in advance.

[ThomKat]

After a year and a half, the ThomKat crew has finally gotten resolution to its engine overheating problem. We've run the gamut of possible causes - from air leaks in water strainers to over sized props to, finally, heat exchangers (HEs). All along, we've had a strong suspicion that our problem was an HE. And that turned out to be the problem. Once the Yanmar rep (finally) got around to inspecting the HEs, he found that the port HE was coated with a material that looked like black Permatex (gasket sealer) and was about as sticky. Apparently, Yanmar's heat exchanger supplier for the series of 75hp engines from which our port engine came, used an improper fluid to test the fresh water side of that particular production lot of heat exchangers. The use of the improper fluid somehow caused the inside of the HE to become coated with a viscous, black material which acts like an insulator. Once that HE was replaced, we've had no further problems with overheating.

During our trek toward finding the cause for the overheating, the Yanmar rep and I checked to see if the engines would reach Yanmar's recommended maximum RPM of 3800. ThomKat's engines would turn only 3550 - 3600 rpm (we are heavily loaded as we cruise most of the time). The Yanmar rep adamantly stated that the engines should turn the recommended RPM (and be run at that RPM occasionally) or it could result in engine or turbocharger damage from carbon build-up that would not be covered by warranty. He recommended reducing the pitch in the props in order to get the maximum engine RPMs up. In order to get to Yanmar's numbers, the prop shop cut down our stock 16x14 props to 15x12. (We later added a #4 cup in an attempt to regain lost performance.) ThomKat's max speed is now 17.1 mph (14.9 kts) in flat water and no wind. I'm not at all satisfied with this combination, but that's another story. We'll get new props, probably 16x13s (thanks Duetto!) before we head south again.

A word to the wise - MV34 owners with 75hp engine serial numbers around E 15308 (ThomKat is hull #75), test your engines to see if they keep their cool and are capable of Yanmar 's recommended 3800 RPM. Several MV34s have had the same overheating problem as ThomKat, and chances are a few more bad HEs are lurking "out there". Unless you test your engines, you won't know you have a problem until that thunder-bumper comes out of the haze and you need to get back to port in a hurry. All that's necessary is to run your engines at absolute wide open throttle for 10 minutes or so (as I mentioned above, that's something Yanmar recommends you do periodically anyway) while watching the temperature gages. If your engine is going to overheat, you'll see it fairly quickly.

If you have any problems, contact an authorized Yanmar representative to make sure you are not jeopardizing your warranty. I'm not a mechanic, nor do I play on on TV - but, if you have any specific questions, I'll try to help....

Tom