CD 25D Yanmar temperature alarm

[n5ama]

I visited my 25D today (the first time in 4 months - bummer) and found that most all was well. I cleaned up a bit and cranked my Yanmar one lunger to prepare for a short outing today. It cranked with no problems but after about 2 minutes the temperature alarm went off. I shut it down and waited a hour to let it cool a bit but it was only idling when the alarm went off. I started it back up and the same thing happened in about 2 minutes.

I changed the pump impeller 6-8 months ago and have run it since replacing the impeller. I checked the discharge today and it seemed to be burping water at about the same volume as in the past. It’s never been a steady stream of water during idle but just spits a little and then every few seconds burps a big slug of water.

The thru hull seems to be allowing water in and not stopped up with barnacles or debris and seems to be moving water. What do you think is going on here?

Thanks in advance for any help,
Tom

[JD-MDR]

I have a volvo. There is an elbow that gets clogged. Its where the water enters the mixing elbow.. I learned to check that first whenever I think its not getting enough flow.

[Frenchy]

Yes, the elbow would be my #1 focus too. If that checks out, try removing the thermostat and see how the engine runs.
Alternatively, see if the thermostat opens when you put it in a pot of boiling water. - Jean

[n5ama]

OK, great suggestions. The elbow is a major check point for me but the thermostat setting up for months also makes a lot of sense.
Both could cause the two minute idle overheat problem.

Thanks!!!
Tom

[Steve Kuhar]

Tom,

You may not have an overheat problem. The 1GM temperature sensor tends to build deposits that cause a false alarm, if that is your problem it is an easy and relatively cheap fix. I once had a really good diesel mechanic who said to forget the temperature gauges and warnings, instead put your hand on the top of the block and count to five, if your hand is still there you are not overheating, if you would not really like to move you hand you are running to cool.

Steve Kuhar

[n5ama]

Thanks SteveI’m tempted to change out the warning sender. I’m not sure where it’s located. The oil pressure sender is obvious but not so much the temp sender.

I guess I should find a manual for this engine.

Tom

[Skipd]

One troubleshooting tool that I’ve found helpful is a infrared temperature gun. They’re inexpensive and a can provide a quick, simple way to check the temp on various engine and related components (exhaust elbows, block, alternator, thermostat housing, transmission housing, stuffing box, etc.). When things are running right get a set of baseline readings and reference that when things seem wrong.
I had the 1GM in a 25D (salt water sailing) and experienced intermittent overheating issues. Did a Rydlyme flush through the raw water cooling system and was amazed at the increased exhaust water flow. Overheating issues cleared up afterwards.

[n5ama]

I had a Fluke IR unit on board when I had the problem but the battery was dead. I’m not sure it would have done me any good anyway because I’m not sure what a over heated reading would be.

When I get this problem fixed, I’ll run a base case and determine what normal temps should be so I can know when I got a problem.

Thanks,
Tom

[Steve Kuhar]

Tom,

The temperature sensor on the 1GM is on the port side of the cylinder head, 90 degrees from the thermostat housing. As long as you are in there, the small plate on the block directly below the temp sensor is an anti corrosion zinc, odds are it could stand to be replaced.

Good luck, let me know what you find out.

Steve Kuhar

[sgbernd]

I assume you have a raw water cooled engine. If you have a heat exchanger, the following is not accurate.

For future reference, another thing to check is put your hand into the exhaust water stream when the engine alarm says it is overheating. Waste water should be cool or at most, slightly luke warm.

If the exhaust water is hot, you aren't moving enough water. The problem is likely impeller/water pump, mixing elbow clogged, clogged strainer, kinked inlet hose, etc.

If exhaust water is cool and plentiful, the water is going thru the bypass rather than the engine, so the problem will likely be one of the following; stuck T-stat, bad temp sensor, internal blockage due to rust, etc.

Steve

[n5ama]

Thanks Steve s,

I’ll check both the sender and the catholic protection. The boat was a fresh water boat all but the two most recent years. I changed the prop anode a year ago but it never occurred to me to change the engine anode as well.

Is there a recommended source for the anode and the thermostat?

The engine is raw water cooled and I’ll check the water temp by hand next time I’m down there. I’ve got some short arms but I’ll have someone hold onto my feet when I reach for the discharge. LOL

Thanks all for the great suggestions.

Tom

[fritz3000g]

The paint on an engine first starts to peel off on the impeller pump housing. That might be another place to look to see if the issue is real.

[n5ama]

Went to the boat today to eliminate two potential causes for my overheating problem. I pulled the mixing elbow and the thermostat. The thermostat appeared a little crusty and the little disk on top was partially open. This surprised me because i expected it to be totally shut. It was warm out today (about 92 degrees) but I didn’t run the engine so the thermostat should probably be shut. It may be frozen in place and that is all it opens. If that is the case, the problem might be solved. I installed the new thermostat with a new gasket.

The mixing elbow was completely unobstructed except for a thin coating of carbon deposit on the inside kind of like a tailpipe on a engine ruling rich. This really surprised me because I was expecting at least some deposits of crud from the water pump going through the tube and into the elbow. I didn’t have a mixing elbow gasket and anyway didn’t have a good way to clean the two surfaces where the elbow connects to the head.

BTW, I was really impressed with the mounting plate on the mixing elbow. They use 3 studs to mount the elbow instead of 4, one on each corner of a square mounting plate. The plate is quite thick and the three mounting points are more than adequate to secure the elbow to the heads. Had they used 4 mounting points, the fourth would have been nearly impossible to reach with a wrench. An American design engineer would have put 4 mounting points and left it to the poor repairman to figure out how to remove it.

My next trip will be to reinstall the elbow. I’ll also pull the water pump cover. I ran out of time today but I just changed the impeller less than a year ago and would be very surprised to find a problem with it.

I guess I could have a faulty out of range temp alarm sender but I trying to work my probable causes from the most likely first.

[mgphl52]

Infrared thermometers are relatively inexpensive and can help pinpoint over heating issues between thermostat, temp alarm sensor and mixing elbow.

[n5ama]

As mentioned earlier, I have a good IR sensor and have used it around various pieces of gear and projects but I don’t have a point of reference for what is normal and what isn’t on this engine. A base case would be great but with the engine running for less than 2 minutes after startup probably won’t give me that.

I’ll definitely take some measurements when I get things back together and definitely take some when I get everything working again.

Thanks,
Tom