Overheating Yanmar 3GM30F

[Alex 2740]

Hello all. I think I have a brain teaser that is currently frustrating me.

I have a Yanmar 3GM30F in a 1992 hunter Legend 35.5. Were currently cruising the south coast of Puerto Rico and a few days ago while on an overnight passage along the south coast of Puerto Rico I noticed that the engine water temperature gauge indicated that she was at 180 F and rising. This was at low RPM's of 2400. At this RPM level in the past she would normally run at 160-170 F. When I throttled her up to 2700 the temp indicator climbed to 190 F. which I had not seen before. When I throttle down to idle the temp would only drop down to 170 F. In the past at idle the temp gauge would normally be at ~ 130-140 F. There was an ample amount of water being discharged from the exhaust however I undertook the following with no luck so far.

1. Replaced the raw water impeller. The old one looked fine. after inspection.
2. Replaced the thermostat
3. removed checked and replaced heat exchanger cooling tube assembly.
4. Removed and cleaned exhaust elbow with muriatic acid. It did have build up on it but not a huge amount.
5. I have removed the belts and hand spun the fresh water cooling pump. It turns smoothly and makes no unusual noises (like ground down bearng ).

I will try to get an infrared heat sensor to see if the sender on the gauge is bad when we get to port however If anyone has any guidance I would appreciate it.

 

[woodster]

check your through hull fitting and hose to the raw water pump you could have some sort of blockage in the area of flow and also your raw water strainer .....


regards

woody

ps also check your seacock valve to see that it is full open

 

[Rick]

Concur. You have checked all the standard stuff that could cause your heat issue. The raw water intake could have a clog. I had a similar problem. When I unhooked the hose from the raw water intake there was flow. Upon inserting a coathanger down and popping out the kelp there was now a geyser!

Best of luck and remarkable work out on the water!

 

[RichH]

Two things to check:
What is the output water flow (out the exhaust through hull) when at normal cruising rpm. Use a bucket and stopwatch - your target for the 3GM is approx. 3 gallons per minute - 3 GPM.

Less than this 3 GPM you have a restriction somewhere in the raw water cooling circuit - debris, worn raw water pump SIDE dimensions or prior broken impeller vane in the piping, etc., fouled raw water injection to the muffler system, etc. etc. etc.

Close to 3 GPM at 'cruise rpm', you probably have a FOULING problem ... the cooling system, including heat exchanger, should be 'descaled'. ..... OR the inlet water temperature is MUCH above 85°F - as this is the design max. inlet raw water temp. for 'most' such engines.

 

[31seahorse]

While checking the raw water supply and strainer basket be suspicious of any angled fittings. Build up, blockage, and marine critters can close those tubes a bit and cause reduced flow. After closing the shut off to the area remove the tubing and poke around inside the fittings that you can access.
We had a similar problem with reduced flow out of the exhaust. We found marine growth like barnacles inside a 90 degree bend. We used a highly technical reamer to remove it.......a bamboo cooking/grilling skewer.
Best Wishes as you continue your travel.

 

[Warren Milberg]

I would also check the inside of your raw water pump, particularly the cam, for wear. You may be getting adequate raw water for cooling at low rpms, but not for higher rpms. FYI, the cam in the pump can wear out and may need replacement.

 

[Stu Jackson]

Also make sure the inside of the rw pump faceplate is flat, if this applies to your pump. A little fine wet sanding is needed on our Oberdorfer 202M-15 from time to time, or I just buy a new one, harder to do where you are.

I check for line blockage between the thru hull and the pump by blowing backwards with the dinghy foot pump. Have cleared two blocks that way.

 

[RichH]

While checking the raw water supply and strainer basket be suspicious of any angled fittings. Build up, blockage, and marine critters can close those tubes a bit and cause reduced flow. After closing the shut off to the area remove the tubing and poke around inside the fittings that you can access.
We had a similar problem with reduced flow out of the exhaust. We found marine growth like barnacles inside a 90 degree bend. We used a highly technical reamer to remove it.......a bamboo cooking/grilling skewer.
Best Wishes as you continue your travel.

Id agree with this scenario. A few times in HOT 90+° tropical water Ive had hard growth well downstream of a 'strainer', apparently the larvae simply went through the strainer and started to grow between the engine and the intake strainer ... I had to remove the hose and beat it with a hammer.

 

[heritage]

You have probably already considered these factors, but if not they are worth consideration:

As I recall, during April along the south coast of Puero Rico, one can expect 4-6 foot waves and a constant east wind, even at night. Eastbound, the engine is working very hard to overcome these forces and you should expect higher coolant temps.

If your motor sailing against wind and waves, the raw water inlet can come out of clear water, especially on the particular tack that raises the inlet the highest. Assuming that the thru hull is not on the center line of the boat.

 

[Allan12210]

A quick way to clear an obstruction in the hoses is to remove the inlet to the strainer and stick your air horn over the end. Give it a couple of honks and listen for the bubbles on the outside of the hull. It usually clears most debris that might have lodged at an elbow or the restricted seacock. You might consider a flow meter like I installed. It is a nice diagnostic tool that at least can give some indication of reduced flow. The flow rate at idle for my 3GMG22 is 2.5 gal/min and wide open is around 7.0 gal/minute.

 

[NYSail]

This one might seem a bit simple, however make sure your radiator cap is on tight and that the gasket is good.... if it lets in the slightest air you will overheat.
Last boat had this problem and it was the last thing I thought of.

Good Luck!

 

[Benny17441]

Hoses get soft and collapse and also get clogged by sediments build up. Check all hoses. Look for obstructions in the raw water intake. Certain obstructions can allow water to flow through at idle but at higher engine RPM may totally block the intake. Check the water flow out of the exaust not just at idle but through the entire RPM range. Best done tied up at a dock in neutral.

 

[srhummer]

I've seen the problem with the radiator cap on a boat I was helping deliver. It got so bad we could not run the engine for more than 15 min without overheating. A pressure test of the Coolant system revealed the problem. The cap was good, she needed a new collar on the top of the radiator because the old one had cracked.

 

[kloudie1]

Gaskets and fittings and hose clamps around the sea water strainer.. It is possible to have an air leak into the seawater intake system at fairly high rpm .. it typically wouldn't leak water when stopped or would barely weep..

 

[RonRelyea]

Where can you get a flowmeter?

A quick way to clear an obstruction in the hoses is to remove the inlet to the strainer and stick your air horn over the end. Give it a couple of honks and listen for the bubbles on the outside of the hull. It usually clears most debris that might have lodged at an elbow or the restricted seacock. You might consider a flow meter like I installed. It is a nice diagnostic tool that at least can give some indication of reduced flow. The flow rate at idle for my 3GMG22 is 2.5 gal/min and wide open is around 7.0 gal/minute.

Flowmeter sounds like a good idea .... any suggestions on where to get one?

 

[Allan12210]

Flowmeter sounds like a good idea .... any suggestions on where to get one?

I was able to find my 0-10 gpm flowmeter at a local electronics surplus store. I had been looking for a while and a couple finally turned up. If you google "10 gpm flowmeter" some show on Amazon. They are about $60.

 

[Cayennita]

When I had a 1987 legend 35, I discovered something similar. My problem was that the key in the impeller shaft disappeared. I did have an extra one just in case I lost one while replacing an impeller. I also had an impeller that the rubber was not glued or whatever to the shaft. It seems that you covered this already. Soft wall on hoses? Jelly fish in the intake system? Try a test by using a bypass hose to another thruhull. The sink is not too far from the intake strainer. BTW, this happened outside of Ponce on the way to St. Croix. Water s very warm in that area. 85 to 89 F.

 

[Dan Johnson]

Overheating...

Had an overheating alarm two fall seasons ago. When I pulled the hose off the intake thru-hull, I got no water flow. I carry a car tire inflator pump and a hose/tire valve fitted up for the thru-hull nipple. Once connected, build up 60 pounds and fire it like a torpedo with the valve handle. Cleared out the what-ever and was underway in less than a half hour.

Don't know if Allan's horn hunk would have worked, but do like where he has his raw water strainer!