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post #1 of 5 Old 04-29-2013 Thread Starter
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Perkins 4108 Overheating

Bought a 1978 Cal 39 about two years ago, and the (Perkins 4108) engine coolant pump was frozen. The local mechanic changed the pump and it worked okay for docking and short motors. When we began using the motor for over a half hour, we noticed problems.

The temperature increases slowly all the way to the point where steam fills the cockpit (at about 190 degrees per the gauge). The transmission also gets quite hot.

This is what weve done:
1. We have removed the heat exchanger for inspection and it is pristinely clean. There is plenty of water coming out of the raw water exhaust. There is no water in the oil.

2. We also removed the rusted-out potable water heater recently but left those lines connected to a little heat exchanger that used to slide into the potable water heater. Should we plug or remove these lines?

3. We ran the engine, in gear, at the dock, at 800 rpm for 50 minutes and the temperature only went up to 140. No leaks/no steam.

4. Then yesterday we went for an engine check, motored at 1000 rpm for about an hour, and the temperature slowly and steadily rose to boiling with steam.

5. So, we removed the coolant reservoir. I was told there was supposed to be a thermostat located under the expansion tank, but when I pulled the tank off, there was no thermostat.
We have received divergent opinions from local marine mechanics about whether or not to replace the thermostat.

6. We read on another thread that the engine coolant water pump gaskets are of differing sizes - is it possible to verify proper gaskets without removing the pump to see if that's the problem?

7. The engine coolant is running through the dual engine oil and the transmission oil cooler. A local mechanic recommended plumbing this cooler with raw water. I'm wondering if the heat exchanger is big enough to handle this load, especially as weve read others with overheating 4108s have solved their problem by replacing the original with a larger one.

8. Weve also read threads about how air in the cooling system can cause overheating, but cannot find any bleed screw. Is it worth trying and if so, what would be the procedure.

FYI: Local water temperature: 79 degrees year-round for what that's worth
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post #2 of 5 Old 04-29-2013
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Re: Perkins 4108 Overheating

You don't mention the out flow from the exhaust, it should be a be solid stream of 8-10 gallons per minute. That's hard to measure but for reference a kitchen faucet is half that.
If it's less than that you have blockage or a bad impeller, or a loose belt to the pump.
I'd suggest that (bad flow) as the most likely problem as that explains the symptoms as presented (adequate at idle, inadequate even a tad above that).

I'm confused on the lack of thermostat - That's what is supposed to control the flow of raw water through the hot bits.
I'd not put raw water through any part of the engine not specifically designed for it and protected with zinc's. The best way to turn a hunk of steel into a hunk of rust is to introduce it to hot salty water.

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post #3 of 5 Old 04-29-2013
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Re: Perkins 4108 Overheating

What Chuckles said plus, Have you pulled the exhaust mixer elbow. It can over time coke up, when I did mine it was half blocked with what looked like a chunk of black coal. Also how is Your water trap, that may need a good clean out. Not having a a thermostat should make the engine run cooler. Other causes of overheating blocked or restricted exhaust and or blocked waterways check and flush both. faulty timing of valves and or injector pump will cause overheating. Start with the easy and hope you rectify it before the expensive stuff. Oh and a cracked head is also a cause. run your engine in gear at 2000 revs tied to you dock watch the exhast water it should be spraying out. then get down and watch the engine as it heats up, you may get to see where the steam is coming from. Before you do this just try running the engine at about 1000 revs with the coolant cap off, the coolant should just move as you have no thermostat If it bubbles or is blown out you have major head issues.


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post #4 of 5 Old 04-29-2013
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Re: Perkins 4108 Overheating

We had asimilar issue recently with our 4108 coming up the central American coast. We got through the Panama canal and cruised for a few months up the central American coast to Costa Rica, where issues started becoming more obvious. Our fresh water pump started leaking through the weeping holes, so we need a new one. Then the motor died off El

Salvador and it took us 14 days to sail 250 mile up to Mexico.

We have pulled our motor out of the boat now. There was very little oil getting onto the valves. The oil pump worked fine, and there was no clogs. We are going to rebuild the motor (as it is already out of the boat and we just bought the boat a year and half ago with poor maintenance records for the motor).

Trouble shoot:

-impeller on raw water pump
-heat exchanger clean
-thermostat working (remove and test in a cup of boiling water)
-belt tight on fresh water pump

-remove valve cover and look for good lubrication (turn the motor over and see if oil comes out the rocker)
-correct atomization in injectors (pull injector, hook up to fuel line, hold paper in front of it, bleed and turn motor over. Do not put your hand in front of it. Look to see a nice spray pattern) or you could just get the injectors refurbished at a diesel tech shop.

After that you may have a blown head gasket, but the smoke would be white if that was the case (or you may just have a small break in the head gasket seal) You might notice water in the cylinders or a bit of hydraulic locking at start up.

Not much else after that other than timing or worn seals, bearings, or liners. Or in my case a little from all the

good luck

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post #5 of 5 Old 04-29-2013
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Re: Perkins 4108 Overheating

Get one of these Infrared Thermometer and Thermal Leak Detector |
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