Cooling water problem

Jack Carr · Post by **Jack Carr** » Jul 27th, '11, 21:00

My 1GM Yanmar is overheating. No water is coming out the exhaust. I checked all of the hoses and raw water filter and could find no blockage. I replaced the impeller (the old one was only months old and looked ok).

In the Spring I had the yard replace the water pump, thermostat, exhaust elbow, and head gasket. Water system has worked fine for the last month. Though probably unrelated the engine is burning a lot oil requiring frequent refills. Dark smoke coming out of exhaust.

When I turn on the engine water appears to be drawn through the seacock and fill the hoses to the engine. What steps should I take to find out what the problems is? Thanks, nothing worse than a boat dead in the water in the middle of the summer.

tartansailor · Post by **tartansailor** » Jul 27th, '11, 22:12

My guess is that the water intake below your sea cock is plugged.

sharkbait · Post by **sharkbait** » Jul 28th, '11, 08:36

I have a piece of hose with female garden hose fitting on one end. I can open the line from the seacock insert this piece of hose and back flush the line from the city main.

RC James · Post by **RC James** » Jul 28th, '11, 18:03

Ran into a problem a few years ago. Ran engine at hight rpms for about an hour, then shut down to sail. Had to restart due to loss of wind, restricted channel, boat traffic, and low flying Navy helicopters.....got a temp alarm......

Crew sailed and owner dove into engine compartment. Verified water from raw-water inlet to strainer to impeller...verified water from impeller to first hose, and nothing at elbow!!~ a little judicious probing w/a sharp/short dental instrument/metal pick into the openings of the engine (after removing the hose fittings) resulted in a rather exciting exit of warm rusty water!! Perhaps a good flushing w/some sort of cleaner would help.

No problems since that episode 4o hours ago, but do make it a point to scrub the raw-water inllet with a brush every couple of weeks. 1GM 7.5Hp Yanmar diesel circa 1981/1982

Neil Gordon · Post by **Neil Gordon** » Jul 28th, '11, 19:54

My MD7A was barely sputtering water out the back. I removed the thermostat housing and went after all the little openings I could find with a wire coat hanger. Lots of gunk was removed, with full water flow restored to normal.

Jack Carr · Post by **Jack Carr** » Jul 28th, '11, 21:29

Thanks for the great ideas. First I'm going start the engine and pull the hose off the exhaust elbow to see if water is reaching the exhaust. If it is I will start searching for blockage toward the muffler.

If no water is reaching the exhaust elbow I will pull off the hoses to the engine and try your probing suggestions with fingers crossed. Thanks again,

RC James · Post by **RC James** » Sep 9th, '11, 17:18

What did you find was the cause of overheating?
Had re-read your original post, and hope that the burning oil wasn't a product of a bad head gasket......

Have found that my early 1GM dipstick is a little pessimistic. The actual stated oil capacity only shows as HALF FULL when the proper amount of oil is introduced to the crankcase.

Previously, I had been filling to the dipsticks's Full mark, and had a marked Moustache at the Exhaust exit. Since measuring my oil input a little more accurately, I have found that the Moustache is missing, and the boat is doing better....albeit w/a cleaner bottom, an unfouled prop, and an occasional stiff brush to the outside of the raw water inlet.

Hoping the fix was cheap and quick .................RC

RC James · Post by **RC James** » Sep 9th, '11, 17:19

What did you find was the cause of overheating?
Had re-read your original post, and hope that the burning oil wasn't a product of a bad head gasket......

Have found that my early 1GM dipstick is a little pessimistic. The actual stated oil capacity only shows as HALF FULL when the proper amount of oil is introduced to the crankcase.

Previously, I had been filling to the dipsticks's Full mark, and had a marked Moustache at the Exhaust exit. Since measuring my oil input a little more accurately, I have found that the Moustache is missing, and the boat is doing better....albeit w/a cleaner bottom, an unfouled prop, and an occasional stiff brush to the outside of the raw water inlet.

Hoping the fix was cheap and quick .................RC

Joe CD MS 300 · Post by **Joe CD MS 300** » Sep 9th, '11, 19:39

Jack Carr wrote:Thanks for the great ideas. First I'm going start the engine and pull the hose off the exhaust elbow to see if water is reaching the exhaust. If it is I will start searching for blockage toward the muffler.

If no water is reaching the exhaust elbow I will pull off the hoses to the engine and try your probing suggestions with fingers crossed. Thanks again,

Has the heat exchanger been serviced recently. They need to be "boiled out"very few years.

Neil Gordon · Post by **Neil Gordon** » Sep 9th, '11, 20:03

Neil Gordon wrote:My MD7A was barely sputtering water out the back. I removed the thermostat housing and went after all the little openings I could find with a wire coat hanger. Lots of gunk was removed, with full water flow restored to normal.

But by the way, engine temp stayed rather cool. Now that I've fixed that, I'm cycling into the red. I'm thinking the clog was forcing cooling water through an exhaust manifold that's partially blocked. Now that the cooling water has an easier path, it must be taking it.

At least I seem to be getting at the problem.

Jack Carr · Post by **Jack Carr** » Sep 10th, '11, 09:59

A few years ago I mounted a raw water filter on the engine compartment bulkhead between the sea cock and water pump at about the height of the top of the engine. As the engine was not pulling any water from the sea and I could find no blockage including the hull grate and the new water pump and impellor were fine, I filled a bucket and pulled the hose off the backside of the water filter and ran the engine. It worked perfectly. Putting the hose back on the filter the water flow stopped.

I pulled the hose off the seacock and opened the seacock allowing water to pour out as expected. I shut the seacock and put the hose back on and took the other end of the hose off the front end of the water filter and water came out. Then the surprise. As I brought the water hose up to the water filter to reconnect the water, the flow stopped. The hose tip must have been above the sea level outside the hull.

This meant I had installed the filter above sea level and I must have lost the siphon effect and the water pump was not able to pull the water through the filter when an air gap occurred. I made sure all air was gone from the system and it worked fine. The question still remains on how air got into the system in the first place to stop the water flow. I'm still burning a lot of oil so when I pull the boat next month I'll have the engine checked out.

Maine_Buzzard · Post by **Maine_Buzzard** » Sep 12th, '11, 05:43

You must have had an air leak in the water strainer. because it was above the water line, it would not show by having water leak out.

Perhaps retightening the cap addressed it?

Neil Gordon · Post by **Neil Gordon** » Sep 21st, '11, 18:12

Neil Gordon wrote:
Neil Gordon wrote:My MD7A was barely sputtering water out the back. I removed the thermostat housing and went after all the little openings I could find with a wire coat hanger. Lots of gunk was removed, with full water flow restored to normal.
But by the way, engine temp stayed rather cool. Now that I've fixed that, I'm cycling into the red. I'm thinking the clog was forcing cooling water through an exhaust manifold that's partially blocked. Now that the cooling water has an easier path, it must be taking it.

At least I seem to be getting at the problem.

Latest update:

Removal of the exhaust manifold showed significant carbonization and partial blockage. Cleaned out and reinstalled, the engine is operating within normal range under load, i.e., a three mile open water test at 2200RPM. Temp rises and falls but it's staying out of the red zone.

Sea Hunt Video · Post by **Sea Hunt Video** » Sep 21st, '11, 21:37

Interesting and timely thread.

I know very, very little about diesel engines. When I purchased my new-to-me Cape Dory 25D I commissioned an engine survey for the Yanmar 1982 1GM. The mechanic was from a shop recommended by Mack Boring.

During the sea trial, while motoring out from the dock, etc., the engine ran at about 2200 rpms. No problems. The mechanic was in the engine "room" (

) checking the engine. When the engine was increased to about 3300 rpms after a couple of minutes the temp light/buzzer came on. We shut the engine down. The mechanic checked a few things but could not determine any obvious cause of the "overheating". He did note the thermostat had been removed.

After waiting a few minutes we started the engine again and while running at 2200 rpms it was fine. When increased to 3300 rpms again the temp. warning light/buzzer came on again. Reducing rpms to 2200 rpms "eliminated" the problem.

The owner/seller said he always ran her at about 2200 - 2400 rpms, even on distance trips, had never run the engine at 3300 rpms and never had the engine temp light/buzzer come "on". He has been absolutely aces with me on so many, many things that I absolutely trust his word.

The mechanic said he could not say for sure what was causing the overheating at the higher rpms. There appeared to be an adequate amount of water coming out of the stern tube.

The service manual for the Yanmar 1GM states that the output rating at 3400 rpms is 6.5 hp and at 3600 rpms is 7.5.

When I have gone sailing with friends with diesel auxiliary it is my recollection they ran them at 2200-2500 rpms. Running at 3300 -3400 rpms seems high but it is what is listed in the Yanmar factory service manual.

I, with my less than "limited" knowledge think it may be a clogged hose, pipe, etc. and that at lower rpms less heat thus less temp. rise. At higher rpms, more heat, higher temp. After all, she is 29+ years old. My docs tell me I have a few clogged pipes as well.

I have noted the possible causes of overheating listed on this thread and will have a Yanmar mechanic I know here in Miami inspect/test again once she arrives here. I do intend to install a thermostat (I think it is Part No. 105582-49200 and a thermostat new gasket. I will probably also replace the water pump and, after inspection, if still OK, will keep as an emergency spare. I will also replace the impeller and keep 2-3 new spares on board.

For a 29-30 year old engine that has only had a few parts replaced (no major overhauls), this was the only significant "issue" found. I was happily surprised.

Oswego John · Post by **Oswego John** » Sep 21st, '11, 22:20

Hi Robert,

There's no way that I'm saying that the following is causing your trouble. But this is something to consider. When a pump is pushing water ahead through flexible tubing, the water pressure will prevent the tubing from collapsing.

When flexible tubing is carrying water to supply the water pump intake, there is usually no problem with the supply at low rpm. As rpms increase, the amount of suction is proportional.

At higher RPMs, when the water supply is insufficient for whatever reason, a vacuum can be created which, in some cses, is enough to partially collapse a soft section of flexible tube which will exacerbate the problem.

Pay particular attention to the water supply line which might be adequate at low rpm but not sufficient when the rpms increase. Some things which might cause trouble is a plastic bag sucked into the intake, partially closed sea cock, pinched hose at bends and other such things that would impede water flow.

Good luck,
O J

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