Engine Overheating-still not cool

[Andy1237]

I thought I had found the culprit of my overheating blues. I can run all day at 2500rpms but over 2800 rpms, a little wind on the nose, pull a dinghy and my high temp alarm was going off.
I finally decided to crack open the front end of the heat exchanger (HX) to see if I noticed any blockage. Right after I pulled the hose off the front end I thought I could see something didn't look right. I couldn't pull anything out with needle nose pliers so I removed the front cap of the HX-sure enough, there was the vain of an old impeller-how old I don't know, could have been the previous owner. I removed the vane, replace the cap and fired it up. (see pics)
A test run at the dock running at 3000 rpm and tied in the slip for 4 minutes indicated no over heating, all seemed good....but the engine still sounded very hollow (waterless) at the higher RPM. At the low rpm there is still a nice "swish-bubble-goosh".

Stay tuned...

 

[Andy1237]

So off the dock and motoring hard across the lake! Everythings running fine at 1800..then 2200..the 2600...may 2800. Just before I get to the dock the darn buzzer goes off! What now? Shut down check things, fire it back up and after 30 seconds or so the alarm goes off and things seem cool. So what do you think-
a) 3GM30s just shouldn't run over 2750?
b) HX still has more crap in it, I need to clean it as described in the forum with a small caliber gun cleaning brush
c) maybe the there is more blockage somewhere along he line?

 

[Benny17441]

Not a) as the engine should run at WOT without overheating. b) is very likely so the HX should be cleaned or flushed. c) is always a possibility so if it persists after cleaning HX then check hoses.

 

[CarlN]

Can you reach maximum RPM (3600 or 3800 - can't remember which on this engine)?

If not, then you are probably over-propped which will overheat an engine exactly as described. The prop may also have a build up of growth on the prop which can create the same situation.

Carl

 

[syoun10]

The 3YM30 had a design fault - the heat exchanger didn't have enough capacity. Yanmar did a design change, so the newer engines are OK, but they DIDN'T inform owners of the faulty engines. They waited for complaints, then changed out bad units under warrantee on a case by case basis. If you weren't aggressive enough in complaining, or early enough, you were out of luck. Some people (me included) who discovered this after warantee ended kicked up enough fuss that Yanmar eventually agreed (again on a case by case basis) to give new hardware, but not labor.

After all the hassle I was put through, I was just glad to get and accept their offer, but in retrospect, I still feel bitter about all the trouble shooting I put in to resolve the overheating problem, and the lack of confidence the overheating incidents caused in my wife's attitude to the boat.

The only good thing is that in my attempt to trouble shoot, I installed a water temp gauge to back up the alarm. I'm very glad to have it now!

Could your problem with your 3GM30 be a similar situation?

 

[Steve Dion]

Is this something new? How long have you had the boat?

Things like hoses, clearing the raw water intake, prop size, clean bottom, impeller condition, belt tightness can all contribute to the problem.

 

[kloudie1]

From here, the next is to check the hoses and the strainer on the suction side of the sea water pump .. A very small air leak at a coupling or strainer gasket can admit air at higher rates but not leak water when stopped. From here, tighten hose ends or replace the hoses if they are more than a few years old.. remove/inspect/rebuild the sea water strainer.. then if still overheating, do the heat exchanger cleaning and check the outlet fitting and the little elbow going into the mixing ell.. Cold be over-propping but usually a lot of black smoke happens ..

 

[sailaway78]

First thing

The first thing I would do is get my paws on an infra red temp unit, and make sure that it is actually running hot. Could very well be a sensor is getting old/tired. I have installed guages because I don't really trust the buzzers. Remember, all manufacturers use the lowest cost things available.

 

[petersea]

Have you replaced your impeller recently ??? the lack of water at high rmp could be a impellar slipping on pump shaft ( there were a bunch of defective impellars a while back).

 

[JK_Boston_Catalina310]

Check out MaineSail's how to articles

You should check out Mainesail's how to articles on his site. There are two that I think would help you.

First, on cleaning a heat exchangers. http://www.pbase.com/mainecruising/heat_exchanger

Second, on using an inferred thermometer to take readings to help find the source of heat issues. http://www.pbase.com/mainecruising/engine_temp

Both are very helpful.

Good luck

 

[zeehag]

i added a second set of gauges to my engine --in the saloon so i can see them when i am inside and others are on watch---i have mechanical and electrical now so i can compare function and mebbe not lose my engine-- good luck--is there a way to fab a larger or more efficient hx???

 

[kloudie1]

Andy.. Just noticed that the baffle in the end plate is not sealing and allowing some water to bypass some of the heat exchanger..That cross plate end should be rebuilt to a nice fresh edge with the same extension as the outer sealing ring so that it presses against the gasket and seals well.. The plate can be cleaned and buttered with a filled epoxy and then filed/machined to the correct shape and length, or a new end cover bought to replace that one.. I would carefully check the other end as well.. May not be all the problem but is not helping..

 

[Andy1237]

I'm almost convinced that I have the undersized heat exchanger. This winter I will clean it out real well and replace the impeller. Current impeller is the blue globe "run-dry" and it could be flexing too much. 3GM30s have the impeller with the pin so sit either works or doesn't. Our old 29.5 had the full metal jacket Groco strainer with exterior screen. 340 has the cheaper Shurflo strainer without exterior screen. I think it could be "restrictive".
As for the prop-folding 2-blade and I never get black smoke.
Kloudie, it think the lip is sealing well enough. This was the first time that cap had been removed. I'll be talking to LaBorde as soon as the storm clears (Issac). Hope all fair well.

 

[Mark Maulden]

In the salt water world, I'd also check the thru hull. Do things grow inside thru hulls/hoses in FW? Or perhaps you sucked up some plastic or something?

 

[petersea]

I'm almost convinced that I have the undersized heat exchanger.

I don't believe the 3 GM engines have a problem with the undersized heat exchangers. It was the the 3 YM engines that did.