Yanmar 1GM Overtemp Alarm / Thermostat

[skipperpete]

Originally Posted by BobbieGWhiz

Correct me, but the more the t-stat opens, the more water can flow through the block, and therefore less of the stream would flow through the bypass. If the t-stat is completely opened, won’t water flow through both paths (in some proportion to the resistance of each path)? The more the t-stat opens, the more water flows through the block. And thus, why wouldn’t a fully opened t-stat be equivalent to a removed t-stat?

Read what Wotname wrote!

[nuku34]

To the OP and others: I don't know the Yanmar being discussed, but It sounds like it is direct sea water cooled (no fresh water heat exchanger).

My Bukh DV20 is also that way, and for those of you who want to understand how the thermostat works in these systems (hint: not the same as a car thermostat) you might want to look at my thread on the matter:
https://www.cruisersforum.com/forums...ed-253789.html

[kenhep]

Had a 1gm for 15 years. Wotname is correct. on the 1gm you can not run without a thermostat, and also as another poster said in this thread there is a small pipe on the front of the engine that can get clogged and this will cause overheating. Every year I would pull the hose off and clear the pipe with a small screwdriver.

[n5ama]

Got the same problem with my 1GM. I get the temperature alarm after about 2 minutes or less running the engine at 1000-2000rpm. I IR checked the head temp which ranged from 150-170F before the alarm goes off. I addressed the usual culprits first by changing the pump rotor and at the same time the thermostat. I still got the alarm in about the same time period. I pulled the mixing elbow and couldn’t find any buildup.

Next I changed the temp alarm sender and had the same few minutes before the alarm. I then disconnected the hose going to the thru hull and was able to blow through it with no problem. The little “L” shaped hose coming out of the top of the water pump and going to the thermostat housing was removed and I was able to easily blow through the connector at the base of the thermostat housing. I checked these fittings with the hose removed the connector appeared to be unobstructed with a ID of about 3/8”.

The strange thing I’ve noticed is there appears to be more water going out the exhaust when I first start the engine than when I check it with the alarm going off. It would seem that it should be constant regardless of the engine temperature.

Can anybody give me some direction here. I’m tempted to pull the thermostat but it’s barely a year old.

Any help greatly appreciated and thanks in advance.
Tom

[Wotname]

Originally Posted by n5ama

.............

The strange thing I’ve noticed is there appears to be more water going out the exhaust when I first start the engine than when I check it with the alarm going off. It would seem that it should be constant regardless of the engine temperature.

Can anybody give me some direction here. I’m tempted to pull the thermostat but it’s barely a year old.

Any help greatly appreciated and thanks in advance.
Tom

It is possible the water passages in the block and head are clogged up with calcium carbonate deposits (boiler scale). This will explain the decreased water flow when hot. If so, you will need an aggressive descale.

Pull the thermostat, temperature alarm switch, zinc anode and the drain cock (red circles). Poke with wire and peer inside to see how clean the water passages look.

Has the anode been replaced regularly (yearly or less)?

You can test thermostat and the temperature switch by heating them in hot water.

Thermostat should operate between 108 and 126 F.
Temperature switch should close at ~150F

[n5ama]

Ok, Thanks!!!
I didn’t think about rodding the holes with the thermostat and temp sender removed. I did plan to pull and test the thermostat, so will pull both, rod them out as far as I can poke with a stiff wire and test the thermostat. I don’t think the temp sender is giving me a problem as it seems to be going off when it should (about 170 degrees). I did change the anode when I first bought the boat about 2 years ago but will check it when I pull things off this week.

This boat had 30 years in fresh water Lake Superior before I transported it down here. I’m sure that doesn’t mean there is no scale built up in the engine but I would think it would be less of a problem.

I sure hope a internal flush won’t be necessary but I’m about at the end of the line on fixes so it might be necessary to bite the bullet and try that.

I really appreciate your suggestions.
Have a great week.
Tom

[n5ama]

How do I accomplish a “aggressive” descale assuming I have scale built up in the cooling passages?

Thanks,
Tom

[Wotname]

Originally Posted by n5ama

How do I accomplish a “aggressive” descale assuming I have scale built up in the cooling passages?

Thanks,
Tom

Short version-

Remove thermostat
Block off by pass hose (double red line)
Remove zinc and refit cover plate.
Remove hoses from water pump and exhaust injection point.
Circulate 'descaling mixture' through the block and head (blue arrows). It doesn't matter which direction you circulate the 'descaling mixture'.

I use a plastic bucket and a small submersible pump (like a bilge pump) to push the 'descaling mixture' through the engine.

Once you think it is clean enough, flush well with fresh water, remove by pass block, refit zinc, thermostat and hoses.

There is a lot of on line debate about what is the best mix to use. Some say CLR cleaners, some say 'barnacle buster', some say vinegar.

I have used vinegar but found it too mild for the job. I now go aggressive with HCl (AKA hydrochloric acid or muriatic acid). Used in industry for cleaning concrete, bricks etc and adjusting pH in swimming pools. You DO HAVE TO TAKE SUITABLE PRECAUTIONS when using this sort of acid. It is aggressive! Here it comes at 30% and while you can dilute it, I find 30% makes for quick job!

Fairly harmless to cast iron though when used for short periods, say 30 minutes. Do flush well afterwards!

[n5ama]

Ok, that’s great info on cleaning up the scale. I’ll get a bilge pump, a 12 v lawnmower battery, a plastic bucket, some 50 molar HC acid and give it a whirl.

I really appreciate your time and the detailed information.

Tom

[Wotname]

Please note - it will fizz a lot when the HCl meets any scale (calcium carbonate).

[bil56]

the hottest part is the head, it is often scaled on seawater cooled engines.
mechanical descaling is often necessary (rod, screwdriver, mini grinder) in addition to chemical ... (I did it on a 2GM)

[n5ama]

Originally Posted by bil56

the hottest part is the head, it is often scaled on seawater cooled engines.
mechanical descaling is often necessary (rod, screwdriver, mini grinder) in addition to chemical ... (I did it on a 2GM)

I’ve put together everything I need but the acid. I’ll go to a local building supply today and see what’s available.

The bilge pump probably has way to much volume for this application so I’ll probably apply a clamp on the discharge to limit that. I’ll have to bring some clamps to mate the hoses I’m bringing to the boat to mate with the smaller diameter hoses used on the Yanmar (another reason to limit the pump discharge). I really don’t want acid flying all over the place when I hook all this up.

Thanks again,
Tom

[Phil_Fr17]

Overheating on a 1GM is simple to fix. I had this engine on board and I had this alarm. Check the seawater pump (impeller), if OK, check the raw water outlet, the flow should be correct at idle and high rpm.
Because the 1GM is a very simple engine with no complicated cooling system AND because these engines or boats never run at high revs (marina manoeuvres), the hottest part, the cylinder head, gets more and more scaled up.


Here is what I did:


# Remove the motor anode, close with a bolt and a seal.
Put (insert) a thick, rigid rubber pipe of the right diameter but slightly larger than the exhaust so that it fits a little in force in it and use it as an extension at the outlet of the exhaust.
I'm talking about the outer side of the hull, not in the engine room, so even the exhaust is cleaned


If possible and much more efficient, turn off the seawater valve, remove the hose and immerse it in fresh water (bucket, several if possible) to rinse the engine well and have only fresh water inside. The less seawater there is, the better the action of the acid.


Do NOT put marina tap water directly into the engine water pump suction inlet, risk of having too much pressure and breaking something !


Suspend a large enough bucket over the exhaust to collect the water coming out of the exhaust.
Use a small 12 volt pump (garden pump driven by a drill or 12 volt pump if you have, no need for a large flow) to suck up what will flow into the bucket. Pump this water back into the bucket which will be used to supply water to the motor pump.
As there is an exhaust filled with water, carefully count the volume of seawater coming out and replace it with fresh water (sucked up by the engine via the engine pump).
# Fill the bucket with one (1) liter of hydrochloric acid, of course top up with water so as not to defuse the circuit.
Personally, I used hydrochloric acid once, then I used a mixture that changes color when the circuit is completely descaled (DKL4, but I'm in France), it's a little more practical if you are sure that the color-change mixture really indicates that the engine is descaled...
Be careful, always put the acid IN the water, never the other way around!!
# Run the engine at idle, watching the level of the mixture sucked in and watching that the bucket at the exhaust outlet does not overflow (to check the flow rate of the pump and vice versa if the electric pump has a high flow rate).
Hot engine, the temperature alarm will definitely sound.
# Stop the engine and let it cool down for 15-30 minutes
# Restart the engine and let it run to allow the acid+water mixture to act until the thermal safety device is triggered (if necessary), otherwise stop it as soon as the cylinder head or the outlet (rubber tube) is very hot. Vary the engine speed from idle to maximum to increase the speed of the mixture and properly descale low flow areas.
# Repeat this process until the flow rate at the engine outlet is correct and test this flow rate at prolonged high speed to check that everything is properly descaled.
# Replace the more acidic water mixture with fresh water, rinse for 5 minutes, repeat this operation at least twice, including one engine at high speed to rinse well.
# Reconnect the seawater circuit.
# Refit the anode or replace it if necessary.
# Test and check for leaks and water flow and if the alarm still sounds.
If necessary, carry out a sea trial (under load) at different speeds.


sorry for any spelling or grammar mistakes. I'm French
Edit for some corrections...

[n5ama]

Thanks Phil, I really appreciate your help. Your English is a whole lot better than my French. I'll give all this a try this weekend when I'm able to get to the boat.

Have a great weekend,
Tom

[Phil_Fr17]

About : " Put (insert) a thick, rigid rubber pipe of the right diameter but slightly larger than the exhaust so that it fits a little in force in it and use it as an extension at the outlet of the exhaust." :


If you can't find this pipe, try putting or hanging the bucket nearest or in the best place, the best location under the exhaust to collect maximum exhaust water without spillage to get the best 'closed loop' possible.
Test by starting the engine and running it at low and high rpm before adding the fresh water and then the fresh water + acid mixture.
Possible that the jet - different - depending on the speed of expulsion, requires changing the place of the bucket... hence my (personal) use of a rubber hose, a hose of the right diameter so as not to waste anything .
Either way, as the engine cleans up, the jet will change and get stronger, that's logical and normal.
Don't forget to increase the engine speed to the maximum possible at the end of cleaning to get to the most inaccessible places in the engine circuit and use the strength of the water currents to act in depth. Stop the engine, let it act, restart the engine after cooling and repeat the operation.
It is also preferable to use a mixture that is not very strong in acid and to act for a long time than the reverse.
Hydrochloric acid can be replaced by sulfamic acid or better, by phosphoric acid, which is less aggressive and which protects soft metals such as bronze or brass.



Don't be too alarmed by the high temperature alarm, it's normal, especially at the start of cleaning.
Let the engine cool enough to circulate the mixture completely when you start it from cold (1/2 hour minimum). Proper descaling takes time, especially in the cylinder head.


Make the brain work before the hands! :-)