Engine Overheating

[PNWE36]

Lots of good advice here. Getting into the fuel injectors can open a can of worms. On this engine I would expect you could go 1500 hours without injector issues. Also fuel injector issues often present with hard starting. If your engine starts well I would be inclined to look elsewhere first.

 

[Feo23]

I seem to have an added modification to the connection between the HE and the mixing elbow. There is a metal, inverted U-shaped pipe about 8 inches high. Hoses run from each bottom end, one to the mixing elbow and one to the HE to complete the connection between the two. At the top of the inverted U there is another outlet, connected to a hose which runs to the bilge. The way the hoses are connected, the inverted U remains upright so the bilge outlet always remains at the top. I have no idea as to the purpose, except perhaps some sort of relief or air bubble bleeding mechanism?

Given my lack of experience, I had no reason to believe this was not standard until I was going through the parts catalog to replace some stripped HE bolts - it was no where to be found in the catalog. I'd like to just eliminate it, although I will have to reorient the little elbow to use a stock hose.

Opinions welcome!

 

[Ralph Johnstone]

I seem to have an added modification to the connection between the HE and the mixing elbow. There is a metal, inverted U-shaped pipe about 8 inches high. Hoses run from each bottom end, one to the mixing elbow and one to the HE to complete the connection between the two. At the top of the inverted U there is another outlet, connected to a hose which runs to the bilge.

Thanks a lot ! My brain now looks like a bowl of alphabet soup after going through that description.

We both have the same engines, the Yanmar 2GM20F, built between 1983-2005.

After reading your description through a few times more, I realize what you are describing is the vacuum breaker. Pull off the inlet and outlet and blow through it to ensure it is not plugged. As it is wide open inside, I would doubt it would plug. Replace it after testing. Do not leave it removed.

Given my lack of experience,

No problem with that, we all have to learn. But it's doesn't mean you go through this process without thinking :

PHOTOGRAPH THE DAMNED THING FROM EVERY ANGLE SO WE CAN SEE EXACTLY WHAT YOU ARE DEALING WITH ! ! !

 

[Davidasailor26]

I think Ralph got it. Sounds exactly like an anti-siphon vacuum break. Its use might be optional depending on the height of the engine relative to the waterline. If it was installed I probably wouldn’t remove it for fear of a siphon forming that could pull water into the exhaust elbow and into the cylinders. Like Ralph said make sure it’s clear, and if so it’s not your problem.

 

[kloudie1]

On my old 34, it looks like this:
Plastic thingie on the top of the "U" is a check valve to stop any siphoning. The seawater leaves the exchanger and goes through the loop to the exhaust elbow.

 

[Ralph Johnstone]

Plastic thingie on the top of the "U" is a check valve to stop any siphoning.

Nice mounting location. Mine was mounted on the side of the engine and eventually managed to leak from the check valve due to the rock and rolling at minimum RPM's coming into the dock. Slowly down the side of the engine, corroding it everywhere as it went.

Was not pleased in the least. Had to strip as much as gear as I could off the starboard side of the engine, wash and wire brush and finally repaint.

 

[heritage]

Does the hose that runs out of the top of the U shaped siphon break have any water coming out of it when the engine is running? If so, the check valve at the top of the siphon break is probably stuck in the open position.

 

[smokey73]

It is a siphon break and I have the same setup as @kloudie1 There is no hose from the siphon break that goes to the bilge and i'm not sure there should be one either. In any case you can buy a new one fairly cheaply. I would not get rid of it and I think it was probably OEM to the Hunter installation.

 

[Feo23]

It does not appear to have a valve, just a hose that runs to the bilge. When I get the engine running again, I'll pull the hose and check for any flow. Everything about the engine is looks to be stock so not sure why it was installed but I will check for any blockages and leave it in place.

Thanks all!

 

[Ralph Johnstone]

Huh ? What ? Howzat ?

I can only offer a completely uninformed and baseless conjecture that the PO by-passed the vacuum breaker and left the old, disconnected assembly nailed to the wall.

Can you photo the hose as it leaves the HEx and enters the mixing elbow ?

This is a shot showing the vacuum breaker attached to the engine as assembled in the factory :

Corrodes the hell out of the side of your engine when it decides to leak.

 

[BigEasy]

Had an overheating problem on my ’88 Hunter with 2GM20F. Would overtemp when running over 2200 rpm. I flushed cooling system, removed heat exchanger & cleaned with a 22 cal gun cleaning bristle brush . (Lots of sediment & some barnacles present). Changed thermostat & heat ex cap with yanmar oem parts, cleaned out mixing elbow, & replaced with coolant / distilled water mixture. Problem solved. And, as someone previously mentioned, be sure to rid the system of any trapped air.

 

[Feo23]

Huh ? What ? Howzat ?

I can only offer a completely uninformed and baseless conjecture that the PO by-passed the vacuum breaker and left the old, disconnected assembly nailed to the wall.

Can you photo the hose as it leaves the HEx and enters the mixing elbow ?

This is a shot showing the vacuum breaker attached to the engine as assembled in the factory :

View attachment 230448

Corrodes the hell out of the side of your engine when it decides to leak.

My bad, I had pulled it out for a better picture. It was not really attached to anything, it was held somewhat upright with the hose to the mixing elbow but was otherwise not attached to the engine or engine compartment. The hose on the left in the picture went to the HE. The reason why I posted in the first place was the vacuum breaker and tubing do not show up in attached scan from the Yanmar parts catalog. The PO had someone replace the mixing elbow assembly about 4 years ago and I guess they got a bit lazy but the hose to the bilge is a head scratcher. I'll see if I can reassemble and replicate your picture - very helpful. Thanks

I don't think this was the cause of my overheating since I went a month last season before I had the problem. Just stumbled across it when I went to check the mixing elbow assembly. I followed all the other other great suggestions on this thread - so far no obvious smoking gun on the root cause.