SailNet Community banner

1 - 14 of 14 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter · #1 ·
Just replaced the water pump on my 34' Peterson (Yanmar 2qm15 wth seawater cooling) All seems well but took her for a ride this morning and the Water Temp. Light came on after about 30 minutes at 2200 RPM. Had temp gun and the highest temp on the engine I could find was 138 degrees F. I will replace the temp gage tomorrow.
Fellow sailor at Marina suggested that I might have to desalinate the engine.
Two questions:
1. Is there an accepted procedure for this and can I do it at the Marina?
2. What is the normal cruising RPM for this engine?
 

·
Registered
Joined
·
2,501 Posts
Pileus :

The motor is raw water-cooled, and with time, it tends to scale up somewhat. My old Volvo MD17C is also raw water-cooled, and after about 20 years I had to strip it (for other reasons other than scaling), and it wasn't scaled too bad too bad, even though it had spent 15 years of its life in Houston and about 5 in Scotland. There was some scaling on the barrels and some pitting on the liners, but not much. cast iron is a forgiving material.
Raw water-cooled motors are cast iron construction everywhere where the (potentially saline) water is in contact with the engine cooling circuit.

If your motor was running OK before you replaced the pump, and still sounds OK, then you have not hurt it.

Take the wee cooling water temperature sender out of the engine....

http://j30.us/files/2qm15_servicemanual.pdf

...and clean it up a wee bit. Start the motor for a moment (only a moment) and water should gush out of the sender hole if your water pump is working fine. That should purge any air in there, if present.

Clean up the sender contacts also.

Try it again.

You can put a de-scaling liquid through the system by catching the hot exhaust coolant in a bucket and running it through the motor again. It might help. I have heard that a fair bit of scale can come out.

The sudden temperature alarm is very unlikely to be because of scaling though. Something else has done it. It is good you are checking the local temperatures with the heat sensor. That temperature of 138 F is not too hot. perhaps the sender has failed?

You could test it by making a makeshift earth from the the sensor body to the motor block, then drop the sensor in to a wee cup of boiling water to see how it responds. better still, is to heat it up slowly in a wee saucepan and check its performance with a thermometer (or temperature sensor). Set the sensor on something non-metallic that keeps the sensor off the bottom of the saucepan or you will get a false reading.

Let us know how you get on.

Rockter
 

·
Registered
Joined
·
5,037 Posts
You first have to figure out if the engine is really overheating or the alarm is not working correctly. Is the water flow out the exhaust normal? If it is and the water temp was really 138F, then the issue is with the alarm circuit. Note that typically the temp gauge is operated by a sender which is variable resistance and the alarm is operated by a temperature switch. The sender and switch are usually separate devices though sometimes combined into a single assembly.
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #4 ·
Thanks. I do not have a gage. Only a warning light. The temperatures I was quoting were from heat gun.
 

·
Registered
Joined
·
79 Posts
I second Rockter's advice about cleaning up the temp sender in the back of the engine, as well as mucking out the chamber the sender goes in. I had this problem on my engine (same model as yours), and when I tore it apart I discovered that there was a buildup of gunk that I think was preventing water from getting to the sender in the first place -- or if water was getting in there, it was only a trickle of disproportionately hot water. After cleaning, the problem went away. Good luck!
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #6 ·
I pulled the sensor, mucked out the chamber and replaced it. It was really in bad shape. Took a 5 mile ride at 2200 and no red light. Hopefully I got it fixed. Looks like I may have to do the engine like Rockter suggested as there was a lot of gunk Did not have time to test the sensor but will look at doing that next week.
 

·
Registered
Joined
·
4,713 Posts
As an aside ,there are two kinds of senders. On is simple off/on for a light and the other is variable resistance for a gauge .I'll bet they're not interchangeable.
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #9 ·
OK now I need to know what the best de-scaling liquid is please. Will try to flush the engine this weekend. As well, what temperature is the thermostat set at. I will replace it as well but the parts person did not have that information.
 

·
Freedom 39
Joined
·
1,156 Posts
When was the last time you replaced the two zincs in the block? If they are very worn they can fall off the stud and pieces could migrate into your cooling system. I don't have a manual in front of me but there is zinc in the front and one in the back of the engine.

What did I do before Google? Found a service manual online here http://j30.us/files/2qm15_servicemanual.pdf
Turn to page 7-8 or 100 and see where the pencil zincs are located if you do not already know.
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #12 ·
Zincs were changed a couple years ago I believe. Have them located but having a real hard time getting them lose. 22mm square head on the covber.
 

·
Freedom 39
Joined
·
1,156 Posts
When I first replaced the zincs on my 2qm I couldn't believe how much crud, scale, zinc pieces etc were in there. I don't recall having too much trouble getting the large square head nut loose on either one. The one of the front of the engine may have required removal of the alternator belt for better access. It's been so long, I do not recall for sure.
 

·
Registered
Joined
·
250 Posts
I too have a 2QM15. My annual maintenance schedule includes replacement of zincs, t-stat, and impeller. Cheap enough.

I also did a Rydlyme flush last year. Made a huge difference. Haven't decided whether to that annually though. Need to balance removal of scale with presence of desirable passive corrosion layer. Maybe triennially.
 
1 - 14 of 14 Posts
Top