3GM30F overheating at 2200RPM.

[coleman]

As I said here; I have had some mechanical issues with my boat. It has been running smoothly and seeming to do fine. When I drive it at 2200rpm continuously for about 20-30 minutes I start to hear the temperature alarm chirp for a good 30 seconds, then light and alarm are on steady and there is steam from the pressure cap on the heat exchanger venting. It runs fine for hours at 1800rpm. The extra load and heat at 2200rpm seems to make it overheat. Makes for a slow day. I had my electrical fans blowing on the engine, crusing with the covers off to allow heat to escape more readily

I am running through all of the typical steps for this problem. The impellers are fine and have been properly re-lubed and assembled, fluids are all clean, exhaust stream looks good and smells normal, seawater inlet and strainer are clear, I plan on removing the heat exchanger and cleaning it (I don't know the last time this was done, anyways) before performing a pressure leakdown test on the freshwater side of the system.

Fortunately cooling system problems are typically simple. I have my hopes high this is not an exception. Are there any tricks/knowledge to why a Yanmar 3GM30F would be overheating, but only above a fairly specific engine speed? Any sort of air-purge procedure for the system I am not aware of, beyond priming the impeller pump when the system is emptied?

Here are some questions I hope can be answered to help me better diagnose:
- What pressure should the radiator cap be?
- What temperature is the thermostat manufactured to open at, and what is the location on the engine?
- I believe that I see the temperature switch for the engine's control panel directly in front/center of the engine above the accessory belt. What temperature does this switch need to activate the alarm/light?
- Does anyone know the thread type and size to install a temperature gauge in place of this switch, or does anyone know an alternate location to install a gauge sender for an accurate reading?
- Best yet: anyone know where an online version of the manual for this engine is?

 

[Steve Dion]

Coleman: I would suggest that you remove the mixing elbow and inspect it.

 

[coleman]

Steve, thanks very much for the suggestion! I've heard this can be an issue but I did forget about it. I'll definitely check that out.

 

[coleman]

Should my heat exchanger, on a 1980 Hunter 37C, look like this one? I see this integral heat exchanger on photos of other boats and Yanmar Brochures on what often appears to be a newer installation, but the heat exchanger on my hunter is a white unit that is bolted to the starboard side of the engine compartment, with the radiator cap just below the upper engine bay access panel. I will post photos as soon as I can.

I do have the very pronounced U-mixing elbow in addition to this off-engine heat exchanger. It's worked fine for years and is likely dirty. I'd just like to verify what I am working with in case I have to start searching for parts!

 

[Jeff]

I had a similar problem with our 3GM30F. Traced it back to a leaky gasket on the stainer basket. It would only over heat at higher RPM's.

 

[Ed Schenck]

Are you sure that you have a 3GM? Most early H37Cs had either a 2QM or 3QM Yanmar. Many of those were delivered as raw-water cooled engines, i.e. without heat exchangers. Then the owners would add an after market heat exchanger. My own 1979 was that way. But it was hose clamped to the engine rather than mounted on the bulkhead. Regardless I think that the mixing elbow is your best bet.

Edit: added two pictures. First is of a 3QM without a heat exchanger. I bought this engine but never installed it. Second is the 2QM that I replaced with a new 3YM. You can see the after market heat exchanger on the top left of the picture, the black tube.

 

[coleman]

3QM makes more sense based on what I have been reading, I'm glad to see someone confirm that. I've been running off of information without having the engine plate handy. Looks like I made a bad assumption, but glad to be corrected and comforted to see this isn't a Hunter installed option. Sort of odd how this is all put together, but Hunter has done some weird things in the past...

Well okay and thanks very much all! Another thing to add to the list of things to do. I'll check the elbow and the other recommended items when I am next at the boat. Should be a few days.

 

[Ed Schenck]

Updated my earlier post with pictures.

 

[coleman]

...Second is the 2QM that I replaced with a new 3YM. You can see the after market heat exchanger on the top left of the picture, the black tube.

Looks like I have the 3QM. I have a very similar system to the 2QM with all of the hoses and accessories connected, and the heat exchanger I have in the boat looks very similar to the black unit you have. Thanks for clearing that. I'll get a good snapshot of the engine plate soon for my records.

 

[akflyr]

I have the same problem. I have also replaced all the impelers cleaned the strainer removed the heat exchanger and had it cleaned. Still over heats!!
I have run the engine with and without the thermastats. Still runs hot. Let me know what you find.
Mark
Whittier Alaska

 

[Steve Dion]

I think that the heat exchanger was an aftermarket on the QM engine. You really do not want to run the engine without the thermostat.

Pull the elbow, you may be suprised. You will need a gasket at a minimum. Getting the elbow removed from the exhaust manifold can be a daunting task. It is good to have two very large pipe wrenches with breaker bars and a torch to seperate the units.

 

[windward54]

Before you take the time to pull the exhaust elbow, you might want to test the water flow first! I had the same engine with the same issue. However, pulling the elbow is a lot of work. Before I pulled mine, I disconnected the return hose from the elbow and ran it to a large bucket. When I started the engine, I could see if the water had a good flow first.

 

[kloudie1]

Yup.. That leaves the elbow.. It can overheat the engine by restricting the water flow but it will overheat the engine from restricting teh exhaust flow as well.. like Steve and Windward said..Not uncommon to have a 1/2" hole or less for the exhaust gas to go through..Sometimes you can knock out the plug and sometimes the salt and carbon deposit is so strong that the elbow will crack as you pound out the restriction.. Good luck with it.

 

[coleman]

Just a follow up on this.

I removed the exhaust elbow. Not all that hard to do at all. A hose pick is an absolute must! Otherwise I would have really fought the exhaust tubing and I can see why folks don't like this task.

First off, the exhaust flow looked almost good as new. On further inspection, the bronze inlet fitting had some corrosion visible in it, so I decided to play it safe and replace the part. I took a reciprocating saw and sectioned the elbow into multiple pieces. Right where the raw water enters the elbow is so corroded that it has nearly blocked the flow of water. Still enough to run at 1800rpm all day long, but not enough to run at rated speed.

New elbow and gasket are going in this week. I'll post photos of the sections I cut, and the new Yanmar part.

 

[kloudie1]

Excellent !!! Glad ya found the problem, Coleman. A little silicone grease does wonders for the next time you have to remove the exhaust hose.. Just remember to clamp it well .. Looking forward to the pictures.

 

[Richard Shelby]

Coleman: You also prevented another potential problem. That mixing elbow has relatively short lifespan in hot seawater, almost sacrificial. I had one blow out from corrosion and spray exhaust/seawater all over the engine. Lotsa fun, huh?

 

[coleman]

As promised, just much delayed, here are some photos of one way the Yanmar exhaust elbow fails.

Water is injected at a low point, must pass above a high point, then out through the exhaust system. The raw water likely pushes out a lot of scale. Anything residual backwashes and clogs the inlet as you can see in my photos. It had just enough raw water flow to prevent overheating at 1800rpm on flat water. Anything more and the engine temperature spiked and I had to shut off the engine to let it cool down (not the right way to cool off a diesel engine but not much choice with engine driven coolant pumps...)

This elbow was many years old and looked brand new on the exterior. There was absolutely no clogging in the exhaust gas portion of the elbow.

I ended up replacing the whole system as it mounts on the exhaust manifold. Look nice, but I am not the happiest with the piecemeal design. I only need to push 25hp or so, so it'll work.

Excuse the 1960's yellow kitchen countertop :neutral:

 

[kloudie1]

Good shots of your cross sections! .. My buddy's two cylinder version of that engine is overheating now after sitting idle for 5-6 years.. I suspect we may have that problem too.