Engine overheat

[mellis18]

My wife and I went for our annual 4th of July parade. Beautiful day on San Luis Bay. However, we had a little problem. After motoring for about 30 minutes my engine overheat light and buzzer came on. I quickly got back to the mooring and hooked her up. After the engine cooled down I removed the impeller housing to take home and inspect. While we were leaving the parking lot a fellow sailor said it was probably the raw water intake...most likely clogged with crap. I thought this made sense because the bottom needs a good cleaning (being done this Friday). The impeller looked excellent so that made think it was the intake after all. The fresh water level was fine and everything else looked good.
Next time I went out I re-installed the impeller. I decided to run the motor again. I ran it for a good 30 minutes and it didn't overheat. Now I'm wondering what it could have been. Some say if the prop is fouled with growth that will overheat the engine when under power.
Any thoughts or advice out there???

1984 Hunter 31 with Yanmar 2GMF motor.

 

[Rick]

Unless you were running her over 75% of WOT (wide open throttle) its probably not your prop AND goo doesnt grow symetrically so if you are in tune with your boat you should have felt a different vibration from normal. The raw water intake is normally a culprit. One tip is to actually unhook the hose from the thru hull and stick a hanger/thin piece of metal through it other than just checking the strainer basket. If your impeller was in good condition that is probably not the culprit either. Might I ask you about the condition, level of your antifreeze. Also, the mixing elbow, depending on how many hours the boat has on it can be a player but this is usually accompanied by black exhaust and lack of RPM at full throttle. Finally, the heat exchanger. Again typically this is a higher hour issue but if you buy a thermal gun (Harbor Freight Tools for a few bucks) you can shoot the temp of the hose as antifreeze leaves the thermostat and enters the exchanger. It should be around 160 to 170 going from the thermostat to the exchanger and then be somewhat cooler as it exits and re-enters the engine. Depends on the temp of your waters because sea water cools the freeze.

Just some thoughts and good luck

 

[Benny17441]

Hard to tell it could be a few things but a fouled prop not likely one of them. We have had floating plastic ice bags partially block the intake and once the engine is shut off and suction relieved the bag has dropped away. Things to check are the strainer, soft collapsing hoses, thermostat and belts for tightness. Not a must, but having a temperature gauge can helpdiagnose and deal with problems. We were once motoring at dusk in unfamiliar coastal waters when our temperature alarm went off. A quick check of the gauge revealed that although the temperature had risen it was showing stable and not at a critical level. We continued motoring for about 30 minutes until we reached our destination at a transient marina. We had shut the key switch off to stop the annoying buzzer and continued monitoring the temperature gauge. Next morning we cleaned the strainer and blew out any debri at the raw water intake with compressed air. If we had not had the gauge it could have made for a long night. Remeber the buzzer will sound well before a critical temperature is reached.

 

[Rick]

Hard to tell it could be a few things but a fouled prop not likely one of them. We have had floating plastic ice bags partially block the intake and once the engine is shut off and suction relieved the bag has dropped away. Things to check are the strainer, soft collapsing hoses, thermostat and belts for tightness. Not a must, but having a temperature gauge can helpdiagnose and deal with problems. We were once motoring at dusk in unfamiliar coastal waters when our temperature alarm went off. A quick check of the gauge revealed that although the temperature had risen it was showing stable and not at a critical level. We continued motoring for about 30 minutes until we reached our destination at a transient marina. We had shut the key switch off to stop the annoying buzzer and continued monitoring the temperature gauge. Next morning we cleaned the strainer and blew out any debri at the raw water intake with compressed air. If we had not had the gauge it could have made for a long night. Remeber the buzzer will sound well before a critical temperature is reached.

Sorry Benny but what did I just say... hello? How about something not mentioned perhaps.. to keep the thread in control.

Its just fun.. sorry

 

[Steve Dion]

This can also be a symptom of a clogged mixing elbow. If you get your bottom and prop cleaned you should have a smaller list of items to check.

You may want to check that impeller again to be sure that it is not spinning on the hub. They have been known to lose the bond between the hub and the rubber.

As I remember there is a lot of weed in that harbor, is that still the case?

 

[syoun10]

I've just installed an alarm that goes off when the raw water flow drops to zero. Earlier, in tracking down an overheating problem (successfully, I might add), I installed a temp gauge to back up the overheat alarm. I'm VERY glad I did that!!!

 

[Don12364]

Two Tips

Was watching a classic 'J' class race on The Solent a few years ago and we were ahead of the fleet which was overtaking us.
Those guys were hard on the wind and with crews of 30 plus they were taking no prisoners.
Suddenly my overheat alarm went off. In a panic I yelled to my crewmates "Turn on all the hot taps". They ran the galley, heads and forecabin basin faucets and the hot water from the hot tank was replaced by cold so any (temporary) loss of seawater cooling didn't matter.
The overheat alarm stopped within 10 seconds and we got the hell outta the way.
Then we had time to sort out the problem.

In the end we needed to blow back through the skin fitting with the dinghy pump to clear it.
Saved the ship though - and us!

 

[amcmahon]

Hey Mellis, some good responses on this. I share the appreciation of installing a temp gage for engine temp. I have had several cases where I could see problems developing without ever triggering an alarm. Once it was a leaf of seaweed near the water inlet scoop - easy solution. More recently went out on a planned overnight and noticed temp running higher than normal. Dropped the anchor and checked the inlet and although a few barnacles, no help when cleaned away. Then checked impeller, but that was good. On to strainer which had some sand build up, but not the cause of problem. After a good night sleep, worrying about heat exchanger, thought about belt. I had not adjusted for over a year (~400 hours). From experience I know to exercise great care here - too tight can ruin water pump, not tight enough and not enough flow. So a slight adjustment and temp back to normal. Temp gage is very valuable.

 

[mellis18]

Temp Gauge

Hey Mellis, some good responses on this. I share the appreciation of installing a temp gage for engine temp. I have had several cases where I could see problems developing without ever triggering an alarm. Once it was a leaf of seaweed near the water inlet scoop - easy solution. More recently went out on a planned overnight and noticed temp running higher than normal. Dropped the anchor and checked the inlet and although a few barnacles, no help when cleaned away. Then checked impeller, but that was good. On to strainer which had some sand build up, but not the cause of problem. After a good night sleep, worrying about heat exchanger, thought about belt. I had not adjusted for over a year (~400 hours). From experience I know to exercise great care here - too tight can ruin water pump, not tight enough and not enough flow. So a slight adjustment and temp back to normal. Temp gage is very valuable.

Installing a temp gauge is a great idea. I also have an hour meter to install so doing both at the same time will be good. I like where you positioned your gauges.
Question - The current sending unit for the the temp probably won't work for the temp gauge. How did you hook up your gauge? Is there a sending unit that will work for both? Do I need two seperate sending units? If I do where do I install the second one?

 

[mellis18]

This can also be a symptom of a clogged mixing elbow. If you get your bottom and prop cleaned you should have a smaller list of items to check.

You may want to check that impeller again to be sure that it is not spinning on the hub. They have been known to lose the bond between the hub and the rubber.

As I remember there is a lot of weed in that harbor, is that still the case?

You're right Steve...there is a lot of weeds and growth in this harbor. And currently there are a lot of Humpback whales :dance:

I had the bottom thoroughly cleaned last Friday. Diver said the bottom looked good structurally and had no blisters :dance: Also replaced all the zincs. After the cleaning I motored around the harbor for a good while and the motor ran great. No sign of overheating. I'm going to install a temp gauge though to have the extra safety net. The sending unit is where I have a question. Any ideas??

 

[syoun10]

The best location for the sending unit (& you're right that it needs to be a different one from the overheat alarm) will depend on the configuration of your engine and the space round it left by the Hunter designer.

I have a Hunter 33 with a 3YM30 engine and the best place I could find was in the line between the thermostat and the hot water heater. But very near the thermostat (so heat would not be lost) and connected to the thermostat by bronze fittings rather that rubber hose. By careful fitting I could just get it in and still be able to replace the companionway steps. Other things being equal, I probably would have preferred to put it in the line between the thermostat and the heat exchanger, but it wouldn't fit, and I'm quite satisfied with my result.