Overheated today

[Ken Cross]

First time out on our new to us Hunter 30 and overheated. We had no such problem during sea trials.

The warning horn came on and I looked at the temp gauge and it was just below 160f. I shut it down and put up the sails for an hour or so. The idea was to go below and check the raw water screen (which was pretty clean) I re-cleaned it anyway and reinstalled. On the way back in there wasn't enough wind to go against the current. I cranked the engine and headed in just above an idle to minimize heat build up. I monitored the temp which remained below 160f but the horn went on again. I looked at the exhaust and water was still coming out so I figured I may have a failed sending unit for the horn. About 5 minutes from our slip I got steam from the engine compartment. Opening the engine cover revealed lots of steam and antifreeze. Since we were in the main fairway of a large marina, I didn't want to try to drop the hook. We just couldn't stay where we were. I came on in at an idle.

My plan is to tear down the raw water pump and change the impellor. If that looks okay, I'll tear down the fresh water side. I also plan to inspect the heat exchanger. I also need to cake a careful look at hoses.

I'm thinking more than one problem. the engine got hot and the indication was only 160.

What did I miss?
Ken

 

[Rick D]

Well, I had a similar issue on my Vision 32 and it's common with the 3GM's and perhaps others. The mixing elbow coked up and slowed the coolant flow. In fact, it was bad enough once that the hose leaked (like yours?) Anyhow, based upon my (several times) experience, I'd start there.

BTW, and not necessarily advice, I purchased a small diameter 3" spring which I put in my drill and sprayed carburetor cleaner while running it in and out of the manifold. Solved the problem. Then I did it annually.

Of course, it could be a lot of other things, like impeller blades in the exchanger, so understand this is just a suggestion.

 

[Ken Cross]

Thanks Rick. I hadn't considered that because it looked like I had adequate water. The elbow is defiantly going on my list.
Ken

 

[Mark Maulden]

Ken, since this boat is new to you, I think you should start at the seacock and be sure hoses aren't collapsing and go through the whole raw water circuit. Once you're satisfied, you'll know how much water is supposed to be squirting out the exhaust. If u don't find a smoking gun, the go through the fresh water side. Something's not happening somewhere. Go to Harbor Freight in EVT and get a cheapie laser therm and shoot different parts of the engine and check ur gauge

 

[centerline]

you mention antifreeze, so this engine has a closed loop cooling system on it.
in that case you could have a failed water circulation pump on the engine, which is separate from the raw water pump.... this would cause overheating even though there is plenty of raw water exiting the exhaust... a calcified heat exchanger could cause the problem also.

 

[bob328]

Check the heat exchanger. It may be partially plugged with salt. Flush it with fresh water from the raw water pump after disconnecting the hose to the mixing elbow. Worked well for me 5 weeks ago.

 

[woodster]

you mention antifreeze, so this engine has a closed loop cooling system on it.
in that case you could have a failed water circulation pump on the engine, which is separate from the raw water pump.... this would cause overheating even though there is plenty of raw water exiting the exhaust... a calcified heat exchanger could cause the problem also.

in most cases if the circulation pump were failed it would be leaking coolant out of the pully shaft ... and maybe even a belt slipping when the engine is running ...it could be a loose belt or even a bad bearing on the pump shaft

 

[kloudie1]

Which engine do you have in the boat, Ken? Good advice so far, I would add that with the alarm beeper on at a temp of 160, (verified, or existing gauge in boat?) ya may have a stuck thermostat.. If a Yanmar, the thermostat action is different from a normal car thermostat in that it must close the bypass and open the main heatex circuit at the same time.. It would unusual for it to fail that way, but not unheard of. So while you are fiddling around in that area, pop out the thermostat and check it in a pan of hot water. your other plans sound fine .. another one might be a plug at the thru-hull .. you can close the valve and remove the hose at the strainer.. if you are lucky, that hose, when turned vertically, will be long enough to be above the waterline in the boat and you can pull up the open end and open the valve without water entering.. then take a flex rod and poke it all the way through the open seacock to push any plastic or whatever out the thru hull.. check for good water flow, then re-attach.
Again, I am assuming Yanmar: the temp alarm should sound at around 220 F.. I would suspect the gauge before the alarm switch.

I had similar problem .. no overheat on sea trial but two days into delivery trip after purchase, overheat from loose alternator/water pump belt, and exhaust ell plugging.

 

[Gunni]

160 is a low running temperature. If the gauge is showing that, I would suspect the sender is not seeing coolant flow. Determine if the steam and overheat was in the raw water circuit, or the fresh water circuit.

 

[Ken Cross]

Which engine do you have in the boat, Ken? Good advice so far, I would add that with the alarm beeper on at a temp of 160, (verified, or existing gauge in boat?) ya may have a stuck thermostat.. If a Yanmar, the thermostat action is different from a normal car thermostat in that it must close the bypass and open the main heatex circuit at the same time.. It would unusual for it to fail that way, but not unheard of. So while you are fiddling around in that area, pop out the thermostat and check it in a pan of hot water. your other plans sound fine .. another one might be a plug at the thru-hull .. you can close the valve and remove the hose at the strainer.. if you are lucky, that hose, when turned vertically, will be long enough to be above the waterline in the boat and you can pull up the open end and open the valve without water entering.. then take a flex rod and poke it all the way through the open seacock to push any plastic or whatever out the thru hull.. check for good water flow, then re-attach.
Again, I am assuming Yanmar: the temp alarm should sound at around 220 F.. I would suspect the gauge before the alarm switch.

I had similar problem .. no overheat on sea trial but two days into delivery trip after purchase, overheat from loose alternator/water pump belt, and exhaust ell plugging.

Thanks for the reply
The engine is a Yanmar 2GM20F. Belts are tight and no indication of slippage, no leaks at pump shafts. The steam seemed to be antifreeze, not sea water. I still haven't been back onboard to look more. I wanted to let it cool before I started working on it. I don't think I can get the raw water hose above the waterline, but I may just remove the strainer cap open the through hull momentarily to check for good flow. The bulge pump will take it away.

I'll be heading back to the boat in an hour or so.
Ken

 

[kloudie1]

Yep.. Gunni is correct.. is why I thought it might be a stuck thermostat; coolant flow being restricted and not allowing a good reading at gauge..
Good Luck with it, Ken.

 

[Ken Cross]

problem found, Thanks everyone

I opened the raw water pump and it looked great. I decided to pull the impeller anyway and found the bronze center isn't bonded to the rubber. I can spin it with my fingers. The impeller still looks brand new. A mechanic suggested it may be evidence of not being run. (The previous owners were living aboard.) I installed a new impeller, but before I run it I plan to change the closed system impeller and flush the system as well.

Ken

 

[kloudie1]

The closed system impeller is a cast iron thingie that is press fit on the water pump shaft.. "no user serviceable parts inside" .. If it isn't leaking, don't mess with the coolant pump..
EDIT: there have been reports of some impellers for this pump failing like that within just a very few hours.. take note and carry a spare.... or three

 

[arf145]

I'd certainly take a look at the thermostat. Generally easy to get at, easy to test, and usually inexpensive.

 

[Gunni]

I recommend that you run the engine and evaluate this fix prior to tearing into the freshwater side of the cooling system. You previously mentioned that you saw seawater in the exhaust discharge. That doesn't square with your broken raw water impeller finding. Once you get everything working you can flush and replace antifreeze.

 

[kloudie1]

If you found an un-bonded impeller and replaced it.. and it did not overheat on sail trials, ya probably have the overheat problem in hand.. replace and test.. and smile if indicated.

 

[jibes138]

How much antifreeze was lost from your coolant tank? in a closed system the usual place for an overheat to release is the pressure cap on the tank. I'm wondering if you could have a leak in the heat exchanger allowing antifreeze coolant to enter the raw water side and slowly depleting the reservoir of antifreeze until it overheats? A very small leak would allow some time to run without the problem being noticed. It still doesn't make sense for the temp gauge to read 160 if you are overheating. Perhaps the thermostat is open but there is no coolant to flow?

 

[centerline]

I decided to pull the impeller anyway and found the bronze center isn't bonded to the rubber. I can spin it with my fingers.

Ken

i think you found the problem... that is rare. usually the fingers tear loose from the center, rather then the rubber separating from the brass core.

 

[BigEasy]

Ken,
My previous boat was a Hunter with a 2GM20F Yanmar. Purchased the boat when it was about 10 years old. Shortly after purchase it consistently ran hot if motoring over 2500 rpm. Changed the raw water impeller but it still ran hot. Decided to do "shotgun" approach & check out the entire system as I knew that PO was not on top of maintenance. I flushed the freshwater side, replaced the thermostat, removed the heat exchanger & cleaned as it was severely calcified, & removed the mixing elbow & power washed the inside. Refilled the system with antifreeze & 50% distlled water. Problem solved--never ran hot again.
I wouldn't bother with replacing the freshwater pump; however, I would replace the thermostat, mixing elbow (Yanmar recommends replacement periodically), clean the heat exchanger ( I used a wire brush from a gun cleaning kit for a 22 caliber rifle), change all of the hoses & belts. This is not an expensive project; however it takes some time and is a PITA! When you finish, at least you will be up to date on the cooling system maintenance & won't have to worry about being caught in a bad situation again due to overheating.

 

[Ken Cross]

Thanks guys. I suspect the water in the exhaust was just inadequate. I'm thinking the impeller may have been turning too slowly. I still plan to flush, check the thermostat, and mixing elbow. I have no idea what previous maintenance has been. The beautiful condition of the things I can see on the boat does make me suspect it had maintenance for most of it's time. The last 18 months a couple had lived on it and I suspect didn't sail much.

My biggest problem right now is I need to spend time cleaning the outside of the old boat (San Juan 28) so I can put it up for sale. It will be in the classifieds here when I finally do that. It's just too easy to ignore it and work on the Hunter.
Ken