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Old 29-08-2010, 18:57   #1
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Engine Running Hot

I noticed that my 25 yr old 4000+ hr volvo MD17D 3 cylinder diesel has been running a bit hot lately... and seems to be getting "worse".

The temp gauge creeps up to the red zone, but not in so technically it is not overheating, but it is definitely warmer that it used to be.

I noticed coolant in the bilge which perhaps came from the pressure relief cap??? when the coolant boiled? I topped up with water, as the reservoir was below min and that would account for high temps. But topping didn't seem to send the temp gauge back to where it was.

My hunches are as follows:

Loose belt or worn belt - tightened the belt as it was loose, but it still could be slipping from age. I will replace the belt.

Pumps - water coming out the exhaust appears normal, but there could still be less than normal with blockage at the elbow. It could also be a damaged RW pump impeller. That one is about 3 years old...

Fresh water cooling pump could be crapping out too, or running slow because of the belt issue mentioned above.

Clogged heat exchanger? Fouled intake?

One odd observation was that running it at 1500 rpm the engine did not run as hot. Push to the normal 2000-2100 and she heats up. Drop it down and she clearly runs cooler.

Oil level was OK and oil pressure was normal.

Sea temps are quite hot these days too.

Any suggestions on how to tackle this problem.
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Old 29-08-2010, 19:01   #2
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Do the 90% fixes first....belt, seacock blocked, impeller (and 3 years is getting old)...fixing these are fast, easy, cheap. If that doesn't work then look at things like the exchanger.
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Old 29-08-2010, 19:37   #3
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Is the engine still making the same power? Is the boat speed the same at 2000-2100 as before? Are you noticing any black smoke?

These symptoms could indicate a fouled bottom or prop. This would make the engine work harder and develop more heat.

- You are losing coolant so the overheating symptoms are confirmed.
- You say you have similar/good flow out the exhaust so the raw water system is probably ok.
- fresh water pumps usually manifest failure as leaks - they are a pretty reliable piece of kit
- There is a possibility that the fresh water system is fouled or the thermostat is sticking.

I would do the simple thing next - thermostat change.

With the fresh water cap off start the engine and watch the fluid level. When the engine gets warm the thermostat will open and you will see the water circulate with potentially a visible drop in fluid level.
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Old 29-08-2010, 19:59   #4
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Losing coolant could be leaking also look for signe of an exhaust leak as well. A bad seal here or there or a salted up exchanger. A hose that dried up and cracked is possible too. There are a few ways this all could be happening but best to tend to it now while the engine still runs. It's easier to find the problem(s). Could be more than one. 4000 hours is not that old.
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Old 29-08-2010, 20:12   #5
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Raw water flow is the most critical item to go after first starting with the impeller. If blades are missing you need to disassemble all the pipes and hoses between the raw water pump and the heat exchanger to find and remove all the broken vanes which can lodge in corners and bends in the hoses and pipes.
- - Of course sea water strainer and inlet/through-hull/seacock are next along with reaming out the tubes in the heat exchanger. The big deal about raw water flow is that your exhaust system is probably made of rubber exhaust hose. Insufficient raw water flow into the exhaust hose and you will cook the hose and it will crack and fail. Now you have a very serious mess and danger as raw exhaust gases and salt water is being sprayed around inside the vessel.
- - After all that switch to the fresh water coolant system. Check to be sure there is no coolant leaking down into the oil pan. Also fill the coolant reservoir and run the engine but not to the overheat point. check to see if you have a lower coolant level in the reservoir. You may be pumping coolant through broken or worn out tubes in the heat exchanger and into the raw water system. Heat Exchangers do wear out especially if not zinc'd properly.
- - Next likely culprit is the fresh water engine coolant pump. Take off the belt and grab the pulley on the pump and see if there is a lot of play in the bearings. If so replace the pump. As mentioned by others normally you may see coolant leaking down the face of the engine into the bilge is you have bad bearings.
- - In very old engines it is common that the coolant galleries and thermostat are clogged with "mud" (corrosion product of the coolant flowing through the cylinder head galleries.). Remove the thermostat and check it for "mud" and/or not operating - staying closed. If there is a lot of "mud" on the thermostat then the cylinder head galleries need to be flushed and cleaned. Normally there are cover plates on the front and/or rear of the cylinder head that can be removed for cleaning out the galleries.
- - If all that is okay and you are still overheating - try buying a new temperature sender and install that. You can borrow an infrared temperature "wand" instrument and point it at the various parts of the engine to see if they are really getting that hot.
- - Finally, obstructions and clogs in your exhaust system from exhaust manifold to riser/water injector to the hose and overboard exhaust through-hull can create excessive back pressure and that will also cause over-heating.
- - There are probably a dozen other things that can cause the overheating from improper propeller size to dragging prop shaft but the above are the most common things to look after first.
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Old 30-08-2010, 05:59   #6
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Gents,

Thanks for all the helpful suggestions. I will put a list of together of possible causes/fixes and tackle them one at a time.

There definitely a some fouling of the boat, compared to when she was dropped in the water and very slippery. Her motoring speed is definitely done a bit (towing the dink is not helping).

We did a great sail a couple of weeks ago - reach in 15+ true and we were doing hull speed and towing the dink, but motoring at 2000 is not getting us there. Perhaps some fouling on the prop???

I think this Fall I will replace all the hoses (except the final exhaust hose which is only about 4 yrs old, the belt (sooner) and the RW impeller and try to flush out the coolant system and definitely inspect the thermostat for mud etc.

BTW no black or unusual smoke or exhaust.

I'll report back the progress and if I can pinpoint what's happening.

Thanks again, Keep the suggestions coming!
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Old 05-12-2010, 09:51   #7
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I am now thinking that my overheating (slight) was related to my fuel leak at the injector pump. For some reason this made the engine run hotter at higher revs because it was not at full power - 3rd cylinder was not getting proper fuel.

Just a guess.

Fuel leak is fixed and engine is winterized so the jury is still out till next spring.

Stay tuned.
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Old 05-12-2010, 11:53   #8
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I hope that's the culprit. I'd be interested in hearing how it works out this spring.
kind regards,
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Old 05-12-2010, 13:29   #9
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I'll let you know. The yard mechanic suggested that the fuel leak which taxed the engine might be the culprit. We'll find out.
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Old 05-12-2010, 17:07   #10
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If coolant is over flowing the pressure cap, that probably means more liquid is entering the system from the raw water side. I had that happen to me once on our Pathfinder engine, and the problem was raw water entering the coolant through the heat exchanger. Easy fix.
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Old 05-12-2010, 18:24   #11
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towing the dink

Quote:
Originally Posted by defjef View Post
There definitely a some fouling of the boat, compared to when she was dropped in the water and very slippery. Her motoring speed is definitely done a bit (towing the dink is not helping).

We did a great sail a couple of weeks ago - reach in 15+ true and we were doing hull speed and towing the dink, but motoring at 2000 is not getting us there. Perhaps some fouling on the prop???
Towing the dink is going to make your engine work harder. Is this something you've started doing recently? If so, it would be worth a test to hoist the dink onto the foredeck, run for an hour and see whether your engine is running cooler.

When you tow a dink you force a sailboat to act like a tugboat. They are not designed for that task.
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Old 05-12-2010, 19:14   #12
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I've towed the dink coastal for years. It is noticeably more drag when the dink's bottom is fouled. I never noticed the engine temp creeping up before when towing even a fouled dink. When I did pull the dink the fall the bottom was not foul as it had been anti fouled.

The prop may be fouled with barnacles and that would kill the efficiency. The raw water intake could be blocked as well, but the effluent seems normal.

The overheating seemed to only occur at the top end of normal engine revs. When we dropped down the temp eases back as well.

My thinking is that to get 2000 rpm with 2 good and one fouled cylinder makes the engine labor to get to that amount of revs... perhaps it's like running it at 2600... don't know what to expect with one cylinder compromised because of a fuel problem.
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