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Old 04-05-2010, 13:45   #1
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Perkins 4-108 NOT Overheating...Yet

Having an interesting problem and didn't see anything quite similar on here, so here goes:

Have a Perkins "New" 4-108 with approx 2200 hours, this is my second season with this boat. Last year, I would have around a cup of coolant in the pan under the engine after a days run.....I assumed it was coming from the hose that runs from the coolant fill cap on the heat exchanger to just above the engine pan. Engine always seems to run OK, right about 180 degrees and 50-60 lbs oil pressure. After engine cooled down, I would top up the coolant to about 1/2 way between the heat exchanger plate visible through the fill hole and the top of the reservoir. I did change the fill cap (same pressure, think it was 7 lbs) and that seemed to reduce the fluid loss but not eliminate it. Yesterday I ran the engine about 3 hours, medium load, temp and oil pressure appeared normal, but after shut down seemed to have well over a quart of coolant under the engine (surprised the temp never got above 180). I haven't actually seen the coolant come out so am making an assumption its from the overflow tube.....will be adding an expansion bottle this week, and then sit there and run it to verify that's where it's coming out, but think 1 quart is way too much and the overflow bottle won't be the answer. Any suggestions/recommendations on where the problem lies?
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Old 04-05-2010, 14:06   #2
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Well your taking the first correct step...

There are a myriad of hose clamps on a marine diesel so if your test comes up negative start checking connections...with a dry paper under the engine you should be able to narrow down the area of leak with the first couple of drops..then zero in with closer inspection.

No mater how new an engine there is always the possibility a gasket did not get set properly or torqued properly so don't rule out any water jacket flanges on the engine until you have the leak located.

I had a leak on the front of my 4-154 no amount of torquing would rectify...I had to take off the actual thermostat housing off the block and head and resurface it as it was badly corroded...so when you say "New 4-108"...what all parts of the engine are actually "New"?... they don't make them any more you know.
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Old 04-05-2010, 14:22   #3
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I'm in the midst of replacing the Fresh Water Circulation Pump. Look there. If you have coolant seeping out from the gasket or from the bearing (like Me!). Pull the pump and replace it. You have to look carefully because the pully hides the shaft and can obscure the edge of the gasket. If it is the pump, it is removed by 4 bolts. Along with the pump you will need to replace the gaskets. There are 2 of them. This is the layup
1: Gasket #1 between block and spacer plate.
2: Spacer plate (this is about 3/16" or 1/4" thick).
3: Gasket #2 between the spacer plate and the pump
4: The Pump.

INFORMATIONAL ALERT! INFORMATIONAL ALERT!
--REPEAT--
INFORMATIONAL ALERT!

The 2 gaskets are different. If you buy 2 of the same you are screwed. Deal with a Perkins part supplier who knows that engine. You are on the east Coast call TAD - Trans Atlantic Deisle. Also , you will have to take the old pump to the parts supplier, they will need to press it off your old pump and onto your new one. The whole thing should run about $160.

If it is not the fresh water pump. Follow the circut around. It may be either a hose or the bottom of the Heat Exchanger. The bottom cap is removable and has a gasket. I'm going to rule out a blown head gasket. Other problems would show up there.
I'm going to rule out internally leaking oil coolers or Heat Exchanger since you see the coolant collectly under the pan.

Good luck, this info is worth exactly what you paid for it and no, you may not borrow my tools.
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Old 04-05-2010, 15:53   #4
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"New" 4.108 was to differentiate my model from the older lowline and highline models (the "new" has an integral heat exchanger, header tank, and exhaust manifold)....as far as I know, it's the original (ca 1987) engine. Thanks both Stillraining and Maddog for comments......haven't noticed any spray pattern or random wetness in engine compartment so was assuming it wasn't coming off the water pump (plus I don't want it to be that ;-), but will check with clean dry paper towels after I get the expansion bottle installed.
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Old 04-05-2010, 17:11   #5
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Good luck - By your discription I have one of the "older" models. A quart is a significant amount. For me that is almost 25% of the entire amount of coolant in my system. And you are right, if it was leaking from the fresh water pump, the pully and belt would be slinging that slimey green crap every where. Don't ask me how I know.
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Old 04-05-2010, 20:14   #6
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There is coolant dye available, leak could be located with "black light".
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