Yanmar 3GM30F Mixing Elbow and Overheating

Bill Roosa · Jul 22, 2014

check your impeller to make sure all the vanes are still there. If that checks out pull the manifolds off the ends of the heat exchange and check if there are obstructions or mineral build up. If all that checks out then the sea side of the inlet may have marine growth restricting it.

RichH · Jul 22, 2014

Check the output water flow that comes out of the stern of the boat using a measured bucket and a stop watch. Your engine should be delivering ~3 gallons per minute out the exhaust with the engine running at 1400 rpm.

If significantly less than 2.5 - 3 gallons per minute, look for an obstruction in the raw water cooling circuit including the injection elbow ... or a vane pump that is bypassing (the area at the *sides* of the pump of the where impeller rotates are worn out, OR you have a 'too thick gasket' being used on the side plate of the pump, etc.).

To check the flow at the injection elbow without disassembling it: disconnect the hose that connects to the injection elbow and run that output into the bucket and measure with stopwatch .... do this with a 'cold' engine and only run only at brief intervals if you have the typical 'plastic' water lift muffler. Compare the outlet volume at the stern to the outlet volume of the hose that feeds the Injection elbow.

And then .....
If output flow is approx. equal to 2.5-3 gallons per minute, then the heat exchanger raw water circuit and usually exhaust manifold) needs to be 'descaled' to remove the fouling in the Heat exchanger and exhaust manifold, etc. ... ie.: probably 'fouled' with mineral deposits.

Use an inhibited commercial boiler descaling compound such as "RydLyme" .... best way to use this is to 'recirculate' it through the raw water circuit. Disconnect the 3/4" hose to the raw water pump and the 3/4" outlet hose from the exhaust manifold, then pump the de-scaler fluid through the engine's raw water circuit .... engine turned on for 15-20 seconds, then off for several minutes. The de-scaler liquid is sucked from the bucket into the raw water pump and the exhaust manifold delivers back to the bucket; you supply the hoses to affect the recirculation. OR disconnect 'after' the raw water pump, and pump the descaler through the engine at a constant rate back to the bucket using an independent 120vac pump.
http://www.rydlymemarine.com ---- for the 'de-scaler'.

If youre running your engine at near full cruise rpm in any salt/brackish water, you really should be descaling every 12 months of total run time (every second season near Annapolis); every 6 months total run time, etc. if using the boat in non-brackish 'ocean' water.

Hope this helps ;-)

kloudie1 · Jul 22, 2014

Elbow looks great. .. I had a problem where at high rpm, the seawater strainer top gasket would allow air into the suction side of the pump, decreasing flow but only at higher rpm.. I rebuilt the strainer and it didn't overheat any more.. Did not leak water when shut down, but clue was green corrosion around the top cap gasket.. probably a very slow weep. The cork gasket had taken a set and no longer sealed completely.

EDIT: I am surprised that you don't have a vented loop in the water line between heat exchanger outlet and exhaust ell inlet. Most 34's I have been on have that to keep from possible water siphoning into the engine when engine is off and you are heeled hard over to starboard

RichH · Jul 22, 2014

Good point by Kloudie, as any air that gets 'sucked' into the raw water circuit will cause the Heat exchange to operate at a considerable LESS rate of heat transfer .... . The 'coefficient of heat transfer' in such exchangers is directly dependent on the ratio of air to water flowing though it. Should be NO air in the cooling water for best transfer efficiency; any air present in the cooling water will seriously degrade that transfer efficiency

kloudie1 · Jul 22, 2014

Yanmar Stuff

Certainly can mark a bucket at 2 gallon interval and put the pump intake hose in there and time with a stopwatch.
For reference, attached picture shows the loop on the back wall of the engine box.

RichH · Jul 22, 2014

Tom-in-Annapolis said:
Any reason I can't test flow with the intake hose in a measured bucket of water? Time how quickly the bucket is emptied?

Not an issue, go for it and keep the hose to the bucket as short as possible and the pump as level to the pump as possible.

Jim Beck · Jul 22, 2014

Has the over heating only been a problem recently or long term? This Yanmar model has had a well-known overheating problem due to an inadequate heat exchanger.

heritage · Jul 22, 2014

Did you unscrew the water inlet fitting from the exhaust elbow? That is where my elbow was clogged. It doesn't take much buildup there to slow the flow of water.

Dan Johnson · Jul 22, 2014

Tom...

The rebuild kit for the Perko strainer should have no bearing on the size of the hoses. The one I bought had the gasket for the top cover and two gaskets for the glass barrell. Nothing pretaining to hoses. The top cap is prone to leaking if you don't get the new gasket seated evenly all the way around as you tighten the two wing nuts.

Also, I reversed the cap on the top so that the closed hole was toward the engine (180 from yours) so that the cap would flop out of the way when I went to pull the strainer to clean it.

Dan Johnson · Jul 22, 2014

Jim Beck...

For the past decade I have been able to run my 3GM at cruising RPM all day long without overheating. Only twice have I had a problem and that was due to weed ingestion (the Susq flats get really churned up after a storm) once and sucking up a baggie once.

This spring I had a water flow problem due to mud daubers clogging the intake thru-hull. A rat-tail flile run down through the thru-hull ended that.

If anything, H34's may suffer from lower water flow from Hunter installing a half inch thru-hull for the engine raw water intake. Some owners have replaced them with 5/8ths or larger (I haven't).

I am unaware of a inherit overheating problem with these engines.

Steve Dion · Jul 22, 2014

Jim Beck said:
Has the over heating only been a problem recently or long term? This Yanmar model has had a well-known overheating problem due to an inadequate heat exchanger.

I do not believe that there was ever an over-heating issue with the GM motors. There was an issue with the newer YM engines. Yanmar was replacing these H.E. when users complained for a period of time. Once that window of time closed it was on the owner to replace them and they are very expensive.

The coking issue on the GM engines is well recorded on this site.

Dan_Y · Jul 22, 2014

*Updated* Attached are photos of a new 2GM20F mixing elbow for your reference. It is surprising how large the exhaust passage is on a new one. I have a bronze Tee before the strainer so I can attach a hose to pull in a bucket of fresh water to flush out the salt water when the boat sits. That's how I found out the pump was not moving water at idle. Needed new impeller and cover. I assume it moved enough water at cruise rpm because the overtemp light and buzzer never came on...but I need to check the temperature sender to see if it actually works!
Dan

Dan_Y · Jul 22, 2014

By the way, my Hunter dealer pointed me to the manufacturer of the vented loop used on the older Hunters like mine. Go to www.scotpumpmarine.com and look at the Products link. The loop on my 2gm20f is for 1/2 inch ID tubing and uses the 1/8-in vacuum breaker.
Dan

Jim Beck · Jul 22, 2014

Tom,

Don't know if mine is an "F" or not. Engine is 2005 vintage. The boat was commissioned in 2006. I had the problem in either the summer of '06 or '07. After proving I hadn't run the engine without coolant, Yanmar did a fix and paid for parts and labor to replace heat exchanger with one that was more robust.

Check out this link: http://www.cruisersforum.com/forums/f54/yanmar-3ym30-overheating-4576.html

Yanmar 3GM30F Mixing Elbow and Overheating

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