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Old 08-05-2012, 05:59   #1
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mysterious coolant system leak

I have a four-cyl Isuzu marine diesel, known as a Pisces.

I have some overheating problems in the past, but seem to have solved them. Now I have a slightly different problem.

I'm getting some sort of a leak in what I believe is the raw water side of the equation. Not a lot, but enough to build up in the bilge at an unpleasant rate. It doesn't seem to negatively affect the proper cooling of the engine.

When I look for the source, I can't pinpoint it -- wherever it's coming from is inconveniently hidden from view. I can't find any leaks at the water pump">raw water pump or around the heat exchanger.

which leads to my next (stupid) question. What the hell is the cylinder-like object that straddles the transmission? There's a water hose coming from one side of it and I wonder if it's some sort of a heat exchanger (for the tranny?) and if the hose from it could be the source?

Any thoughts much appreciated.
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Old 08-05-2012, 06:32   #2
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Re: mysterious coolant system leak

I've owned two Isuzu vehicles. They are known for bad water pumps. Check the under side of the pump. Between the bearings there is a weep hole. Look to see if it's wet. If so, it's time to change the pump.

A heat exchanger would have at lease 2 hoses or more depending on how it's mounted.

If the motor has over heated, it could be a cracked hose or loose fitting.

Why did it over heat?
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Old 08-05-2012, 06:44   #3
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Re: mysterious coolant system leak

delmarrey,

It's not the raw water pump. It overheated because the heat exchanger was not properly secured and migrated down, causing an air lock (I think). That's solved. It's just so bizarre. I have had issue after issue with this engine and now that she seems to be running at the right temp, I have this stupid leak. Wherever the leak is, it seems to be coming from the right rear quadrant of the engine as you face aft. It's so freaking inconvenient to work on anything, too. My theory is that while access was probably never good, the repower with the Isuzu (under a previous owner) left even less space in the engine box. What I wouldn't do for real access to the engine!
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Old 08-05-2012, 06:59   #4
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Re: mysterious coolant system leak

... thanks always for your input. You're one of the few people who have experience with this engine. Is there any other possible source for a leak?
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Old 08-05-2012, 07:46   #5
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Re: mysterious coolant system leak

I have had to chase similar leaks with the same level of frustration. The two other places are the stems of any valves in the system. The hot water/coolant combination does not do the valves (like to adjust flows to your hot water heater) any good---and I have had them leak at the stem. The other is to go around and make sure that every clamp is tight and does not have some foreign object or crack in it. It is frustrating. Took me months to find one tiny leak.
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Old 08-05-2012, 08:11   #6
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Re: mysterious coolant system leak

Quote:
Originally Posted by sneuman View Post
Wherever the leak is, it seems to be coming from the right rear quadrant of the engine as you face aft.
Actually, I've owned 4 Isuzu's I forgot about the I-marks.
If you know about where the leak is, then that's the main place to look. Sometimes a pinhole will start right at the edge of a hose clamp. This is one main reason to keep machinery clean, so one can find any new leaks that show up.

I use to maintain two huge 4-stage CNG compressors (4000 psi) and if is wasn't for keeping the things spit shined it would have been a bitch to find all the little problems they had.

So get down in there with a mirror and flashlight around the hose fittings and you should find the source.
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Old 08-05-2012, 09:27   #7
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Re: mysterious coolant system leak

Try wrapping, or cable tying, some folded up paper towels around the suspect areas. Even a tiny leak is obvious and you can see from the stain if it's raw water, coolant, oil etc.
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