Yanmar Engine Overheating?

[neilacarter]

Hello all -
New member here, and a new boat owner. Though I've been sailing for 7 years, I was only crew until my recent purchase of a Catalina 440. I'm hooked.

I have an issue that has come up however... Two weeks ago the boat had a fresh coat of bottom paint applied. She was in dry dock for about a month. After launching the boat the temperature gauge on the binnacle has been telling me that she's overheating.

To my knowledge there are two different temp sensors on the engine - one connects to this temp gauge and the second is the "dummy" alarm that will sound if the engine gets too hot. What happens when I run the engine is that the temp gauge will climb up to be pegged, and then periodically bounce between 180 degrees (normal operating temp) and maxed. The secondary alarm never goes off. I have noticed a very small amount of red fluid in the catch basin underneath the engine (by small I mean about an ounce or less), that appears to be the same color as diesel engine coolant.

The engine is a Yanmar 4JH3-TE. I've never had an issue with overheating until now. I've investigated a few things, but I should note that I am not skilled at diagnosing beyond the below, nor a mechanic (though I am currently in the process of taking a marine diesel engine maintenance and repair course locally to learn how to be more self sufficient).

I have...
1) checked that water is correctly flowing out of the exhaust vent, per normal.
2) checked that all the seacocks are correctly opened to allow water to flow through properly.
3) ensured there are no obstructions in stainless raw water filter
4) checked coolant levels, and added about 1/4 cup of fresh water
5) checked fittings to make sure they are tight... to my eyeballs and limited knowledge they look ok.

Some thoughts others have shared with me are that there may be an air bubble in the system that needs to be bled out, or that the temp gauge may have failed, but that everything is actually ok.

I intend to swap the temp gauge to see if that fixes things, since that is easy to do - I'll report back on whether that fixes it. Unfortunately I do not know how to bleed air out of the system, so if anyone has very instructive steps and pictures of how to do that I would be really appreciative. Also, if there are other things to consider I'd love to hear them.

Thank you all in advance,
Neil

[Bash]

Welcome to the forum.

I have that same engine, and have never seen mine bounce back and forth between one temperature and another, as you're reporting. To get mine to run hot is a slow process, and it tends to cool off slowly as well.

If you're really running at max heat on the gauge, your engine should be blowing steam out the exhaust. If it's not doing that, swapping the gauge, as per your plan, would be a good first step.

[Paul L]

A laser temp gauge is helpful to check the engine and see what the actual temperatures are of various components. You can get one cheap at Harbor Frieght.

[sailorchic34]

If your getting good water flow out of the exhaust then either the thermostat is bad, the heat exchanger is partly clogged (but flow would be less too) or the temperature sender/gauge is bad... As the temperature is going up and down, I'm betting thermostat....

is there a strainer over the exterior thru hole. Sometimes they get gummed up with paint too. But if the raw water flow is good then your probably ok there.

[Tropic Cat]

He's a new boat owner....... did you close all seacocks before you hauled out? Did you open all of them since back in the water? Sounds like his cooling line is clogged or shut off.

[Cotemar]

I agree about getting a handheld laser temp gage to point at the engine parts to see hot spots.

Even though you see cooling water going out. I would pull the impeller and make sure that all the impellers are attached and that the hub is not broken free from the rubber. This was a common recall problem with the impellers and over heating

[ReMetau]

Sounds like a bad gauge or sensor. I agree that you need to verify using a laser gauge.

[neilacarter]

Thanks for all of the feedback folks - I really appreciate it.

To answer some of your questions:
- I did not close any seacocks during haul out, they remained open.
- I did check to make sure all of them are still open, now that she's back in the water.

Regarding this specifically, wouldn't there be a lack of flow if they were closed or heavily clogged? I'm seeing proper flow through the filters and what appears to be the correct amount of water discharge out of the exhaust.

- I like the idea of a laser temp reader - I'll look into purchasing one!
- There is no steam coming out of the exhaust.
- I may look into the impeller, but since that is kind of a pain (from what I've read) to get at, I'll only do that if replacing the temp gauge doesn't resolve the issue.
- Regarding the heat exchanger, does someone have a good picture/diagram of what that is and where it is located? As I mentioned, I'm not particularly skilled at all of this, though I'm in the process of taking classes to learn about it.

Here's the plan of action for me right now:
- replace temp gauge, see if that resolves it
- if that doesn't work, replace the sensor on the engine
- if that doesn't work look into bleeding any air bubbles out, and check to see if heat exchanger is gummed up, check the impeller to make sure it is working properly

For that last one I'm going to really have to investigate how to do those. Fun times!

Best,
Neil

[ReMetau]

A laser sensor to actually check your engine block temperature would be a lot cheaper than just replacing your sending unit and gauge, and then you will always have it for the next time.

[Bash]

Originally Posted by neilacarter

Here's the plan of action for me right now:
- replace temp gauge, see if that resolves it
- if that doesn't work, replace the sensor on the engine
- if that doesn't work look into bleeding any air bubbles out, and check to see if heat exchanger is gummed up, check the impeller to make sure it is working properly

Sailorchick's suggestion to check the thermostat was right on target. A good thing to add to your list.

If you bought the boat used, don't just check the impeller, replace it. They're cheap, and should be replaced every other year at a minimum. Some folks replace them yearly.

[sneuman]

You could have an air lock as you suggest. Another possibility is a clogged heat exchanger - you could remove it and have it pressure tested at a radiator shop.

I don't know Yanmars, but on my Isuzu, there's a hose from the fresh water pump on the engine block to the heat exchanger. If you disconnect that hose and back fill the pump with coolant, that might force an air bubble out.

Worth a try.

[tandem tantrum]

Plus one about having a fresh impeller!

[chrisjs]

The only time I had a temp reading problem on my Cummins, it turned out to be a loose electrical connection. Suggest you check all relevant connections from engine to display. There may be no real temperature issue.

[Outwest34au]

Check sender wiring.

More likely a sender failure than gauge.

Check the thermostat in a pot of boiling water if you like, they don't fail as often as they used to 20 years ago tho. Always a good idea to drill a 1/8" hole in the side flange of the thermostat to act as a self bleeder for filling if it doesnt have a "tickler".

A small steam pocket (yes a hot air bubble) can move around the end of the sender, this shows as HOT. With some troublesome engines I have tapped a 1/8" BSPT thread into the thermostat housing or taken a bleed line from the top corner of the head and run that to the top radiator tank. It is a constant air bleed and bypasses such a small amount of water cooling won't suffer.

[Wotname]

Yes, check wiring / connectors as suggested by last two posters. Wiring loom connectors account for many intermittent type faults.