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Old 16-04-2007, 15:15   #16
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Alan - I have read many of your posts and respect your experience. In my case that air block was the problem. It would not move until vented. I belive the problem was also compounded by using a wrong thermostat installed by the PO. Combined, these two worked together to mind screw a few mechanics on the overheating symptoms. It's always the simplest things.
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Old 17-04-2007, 00:00   #17
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Maddog, don't get me wrong, I am not suggesting a fault like this could nto happen, I am just thinking Capt Kens problem is different as (if I understand correctly) he seems to be regularly and continually topping up with water. That makes me suspect it is a different issue to what you had.
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Old 17-04-2007, 09:25   #18
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Quote:
Originally Posted by Alan Wheeler
Maddog, don't get me wrong, I am not suggesting a fault like this could nto happen, I am just thinking Capt Kens problem is different as (if I understand correctly) he seems to be regularly and continually topping up with water. That makes me suspect it is a different issue to what you had.
I agree, I was never losing coolant. It's the only system in my engine that doesn't leak. I am guessing that he has a pin hole leak inside his inter-cooler and it is going out with the exhaust. Do the preasure test over a day and see what happens. Before you rip the head off. Drain the raw water out of the inter-cooler and do the pressure test again. If you get any coolant it's time for a new inter-cooler or a repair.
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Old 30-04-2007, 06:02   #19
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Perkins 4-108 Overheating Up-date ....

I've been unable to pin down the EXACT reason for my overheating/coolant loss problem, so I'm incorporating almost all the suggestions made so far.

First, I've replaced both hoses leading to and from the hot water heater. (All the other engine hoses are visible and appear to be in good shape.)

I've replaced the coolant "over temperature" sending unit. For reference my 4-108 and maybe others have two temperature sending units; One is of the variable output type and leads to the temperature gauge. The other is a normally open switch that simply closes when coolant temperature exceeds 277 degrees (!). This switch was apparently not operating or not correctly wired. I've replaced it with a new one and, using new 12 gage wire and fittings, wired it into my "loss-of-oil-pressure" alarm circuit: a nice LOUD bell.

Per Maddogs suggestion, I've installed an elbow that will enable me to top up the coolant at the new water temperature sensor on the highest point in the cooling system.

Per Chucks suggestion, I've installed an expansion tank with a lead to the overflow tube just under the cap on the heat exchanger. If this works as advertised I should be able to monitor coolant level more easily because it will be more visible. (I can understand how coolant can be pushed out of the engine here, but I'm mystified how it can be drawn back in considering the 7 pound pressure cap ... but so be it.)

Well, if everything works my overheating/coolant loss problem is solved. At least, if she does overheat the new over temperature switch should give me time to shut down the engine before she seizes.

We're soon to depart mid-Florida toward New England. We'll be sailing outside and motoring in the ICW depending on weather. About 1500 miles North and then 1500 miles back in the Fall. The voyage is sure to include lots of motoring. Wish us luck, and thanks for all your suggestions.
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Old 30-04-2007, 07:03   #20
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Originally Posted by KaptainKen
Perkins 4-108 Overheating Up-date ....

(I can understand how coolant can be pushed out of the engine here, but I'm mystified how it can be drawn back in considering the 7 pound pressure cap ... but so be it.)


Pressure caps have two valves, one to let out coolant when the radiator pressure is too high, one to let coolant back in when the radiator is under a partial vacuum when cold. What has been too long ago for me to remember, did radiator caps have the in valve before overflow tanks existed just to relieve the partial vacuum when cold? So I believe that there is a possibility that just adding the expansion tank without the correct cap does you no good. If you look at your cap closely, you can see how the two valves work.

John
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Old 30-04-2007, 09:12   #21
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Please keep us updated. The best repository for Perkins knowledge is in these forums.

Good luck with your trip. I think you'll be OK.

Did you try the preassure test? Also, what is the location of that second sender? I have only been able to locate water temp sender out of the head/manifold near the top of the engine just behind the coolant tank and the oil pressuer sender at the opposite end just below the injectors. Does that make sense?
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Old 30-04-2007, 21:30   #22
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One of the responders stated that he overheated at 2500 rpm. Check the prop pitch, you may be over propped. I was and changing to the propper pitch fixed it and now I go to 3600 RPM without overheating.

Now as to the original poster, the water loss. I havent heard one person mention the rubber caps on either end of the heat exchanger. I think I have a small leak there the clamp holds the boot to the cooler stack. If it leaks here you can loose fresh water into the salt water track and out the exhaust without any evidence of loss in the bilge ore elsewhere.

Mine looses about a cup a day from the freshwater track and I have just about come to the conclusion that the boot seal is leaking and its going out the exhaust. Thats my next project.
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Old 30-04-2007, 23:22   #23
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Quote:
One of the responders stated that he overheated at 2500 rpm. Check the prop pitch, you may be over propped. I was and changing to the propper pitch fixed it and now I go to 3600 RPM without overheating.
That was me.
Not over propped, get 4000 RPM..Right on the money.
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