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Old 20-03-2017, 22:35   #1
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Kohler 5E/4EF 7.3E/6EF Generator Overheating Resolved

Running higher temp or shutting down on high water temp:
I had a Kohler 6EF generator with intermittent running hot issues. With the help of online boating forums I have resolved the issue and all is well. However in the voyage to have a cool running Kohler I read many, many forums. The generator has the Kawasaki engine FD501D, with the Kohler standard maritime cooling equipment. To help others in this quest, I have assembled this listing of items to check and some resolution methods I have gathered from the forums and/or utilised myself. The post title covers 4 units, as per the Kohler Manual TP-5985. Section 4 of that manual has the trouble shooting table for the cooling system. Service Manual is TP-5986. Parts Manual is TP-5987. Kawasaki engine FD501V and Kawasaki engine FD501D supplementary cover the Kawasaki engine. In reality the FD501D supplementary does not contain any information of interest with respect to the Kohler set. All manuals are freely available via a google search on the www.

Issues other than the cooling system to also consider:
  • Correct fuel
  • Clean the fuel filter on the inlet
  • Correct grade and clean oil
  • Correct level of oil.
  • The oil level apparently needs to be checked by removing the dip stick and placing back in without screwing in.
  • Oil sender can also provide a shutdown engine signal
  • Clean air filter. This is checked by removing the 4 large cover bolts and opening the filter housing. OEM filter parts can be hard and or expensive to track down. A local lawnmower shop or rubber shop have filter material that can be cut to shape.
  • Correct spark plugs and gaps.

Cooling System:

Radiator cap is correct pressure and is sealing and relieving.
  • This can be seen by the water level going up and down in the expansion tank during running of the generator.
  • Check the overflow hose is complete and not leaking and it goes to the bottom of the overflow bottle, so it only returns coolant to the system.
If level is all over the place, shutdown, cool, remove radiator cap and then run with cap off. If you see bubbling that builds up, you may have blown head gaskets. ( See YouTube for typical effects)

Replacement of head gaskets is not covered here, but can be achieved if you have standard small motor knowledge and access to a torque wrench. Kawasaki engine FD501D mechanical manuals are available online with good details on teardown and rebuild. Allow 3 good days if you have good access and materials gathered.
  • Gaskets needed include:
  • Head gaskets (2)
  • Inlet manifold gaskets, L & R are different (2)
  • Head exhaust manifold gaskets (2)
  • Carburettor to inlet manifold gasket (1)
  • Heat exchanger manifold O- ring (2)
  • Engine block water outlet O-ring (1)

Check hull through valve is fully on and full sea water flow past the inlet strainer to mechanical pump. This is achieved by pulling hose at outlet of strainer.
If low sea water flow
  • Check through valve inlet cover on hull to ensure clear of marine growth
  • Clean strainer
  • Check though valve porting and valve are clear of marine growth
  • Check flexible hose is clear of marine growth or scaling.

Check the mechanical pump seal has not failed (sea water around generator is an indicator)
  • If it has then follow the removing pump sequence.
  • Replace seal.

Check pump is pumping (disconnect output hose at outlet of exchange cooler to see the flow under cranking only – but do not run like this.)

If it is not pumping take the cover off the pump and try to rotate it with the impeller with your fingers. It should feel locked in place.
If locked, then move to next step of checking condition of impeller.
If it moves, then remove the pump to replace coupling.
Achieve this by:
  • Loosening both hose clips
  • Removing four holding bolts
  • Remove complete pump
  • Don’t damage the seal face.

There are two allen key bolts on the housing that rests behind the water pump, the bolts are at the 12 o'clock and 6'oclock positions. Remove those bolts, they are short.
Remove the housing and you will find the shaft coupler (probably black in colour, with interior splines, or parts thereof scattered around.)
Replacements are a yellow plastic coupling that couples the drive motor shaft to the mechanical pump.
Reinstall all.

Check the mechanical pump impeller is fully complete and sound.
  • Achieve by removing three of four bolts, loosening the 4th and rotating the cover plate.
  • Take notice of rotational direction of the impeller blades so you replace the same way.
  • Removed impeller. Note the keyway. Ensure all blades of impellers are attached.
  • If missing impeller pieces, keep stripping down sea water side of system until all pieces are accounted for. If you don’t these pieces can and will continue to cause issues.
  • If you are this far in and the impeller has 500 run hours or 1-year-old replace the impeller anyway. [ Some forum members tend to change @ 150 hours]
  • Kohler Part No. 359978

Remove output hose from cooler post the anti- syphon valve where it attaches to the elbow into the manifold. Remove the elbow from the manifold and remove marine growth in the elbow.

Since the output house is now removed, and the pump is off, backflush the cooling circuit with at garden hose. Watch for impeller pieces (even if yours is good, as the last owner / mechanic may have not checked after an earlier impeller failure)

Check all the hoses for internal marine growth or scaling.
  • From inlet strainer to pump.
  • From pump to exchanger. This can be a struggle, but should be done as build up can be found at the inlet to the heat exchanger
  • From exchanger to inlet elbow via anti syphon U bend.
  • Check anti- syphon duck valve is flexible.

If the impeller parts are missing and pulling the hoses and or flushing does not find them, remove the heat exchanger.
  • To remove the exchanger, ensure you have drained the fresh water cooling system first. Capturing the coolant is easy if you remove the coolant hose above the oil filler area. Take care as the elbow it attaches to is plastic.
  • Remove the sea water hoses each side of the cooler.
  • Can be achieved by loosening the hose clips, the hose will let go when you pull the exchanger

Loosen the 4 bolts on the exchanger flange.
  • At this point, even when pre drained, some coolant water will run out.
  • Carefully remove the exchanger from the two seawater hoses
  • Carefully move the exchanger forward as the thermostat is in the inlet side of the exchanger.
  • Note direction of installation of thermostat, spring towards the filler cap.
  • Shake the exchanger and listen for plastic parts rattling around.
  • Flush the exchanger out with garden hose.
  • If marine growth internal to seawater side of exchanger, clean.
  • Exchanger has two O-rings that will need replacement when reinstalling.
  • Check thermostat in boiling water to ensure its opening, if not replace.

Check overheat switch. This is beside the inlet elbow.
  • Can be removed and tested in hot water in saucepan with multi- meter for open /closing.
  • After cleaning, reinstate all.

Fulling the internal coolant system is problematic.
The mixture of coolant to clean water should be as per the Kohler recommendation of percentage glycol to water and or the coolant instructions.
The Kohler manual has this procedure:
  • Loosen air bleed screw located on top of engine to allow trapped air to escape.
  • Place a rag around the screw to prevent coolant spillage onto block
  • Remove pressure cap located on top of engine and fill with recommended coolant until level is just below overflow tube opening.
  • Tighten bleed screw when coolant, free of air bubbles, starts to flow. Replace pressure cap.
  • Start generator set and allow to run for 20-30 seconds. STOP generator set and recheck coolant level by removing pressure cap. Repeat procedure, as necessary, unit coolant can no longer be added.

Other writer’s options on this if above method not successful include:
Continual to fill slowly for a minute, letting the bleed port bleed the air out, and then burping the system by squeezing the coolant hoses. Repeat by adding more coolant.

Using a 6” piece of tube the size of the filler cap to create a head of coolant. Maintain head, while squeezing the circulation hoses, and alternatively opening the bleed screw. The additional head pressure apparently helps burb the system.

Using a hand vacuum pump:
  • Fill the overflow bottle completely and leave lid off
  • Install the radiator cap
  • Attach a tube nibble to the bleed port
  • Run a clear tube to the tube nipple, connect an oil change extractor vacuum bottle or similar.
  • Pull a small vacuum on the bleed port.
  • Watch the bubbles travel up the tube from the port until they slow
  • Gradually pull more vacuum so coolant is now flowing, keeping filling up the overflow bottle. Do not let the overflow bottle bleed dry! Do this slowly with about 1 litre. Reduce vacuum and watch the bubbles travel up the tube reducing.
  • Takes patience, but when the bubbles slow, remove bleed nipple and replace bleed plug (using thread tape)
  • Top off overflow bottle to L mark, replace cap.

Run the generator, watching the overflow bottle to ensure the coolant stays level between the L when cool and H when hot.
  • If you have an IR temperature gun you can see the temperature change on the cooling manifold when the thermostat opens.
  • After running for 5 minutes on load, shutdown, let cool and check the coolant levels
  • Water temperature range 91-104°C (195-219°F).

Other issues and resolutions with the mechanical water pump.
  • Install a dry run impeller available from online vendors ( i.e. Global Marine )
  • Remove impeller totally and change out to a mains powered pump such as a 230/ or 120Vac March pump or similar meant for air conditioners, These pumps are not self-priming, they have to be below the water line, but will lift water a significant height. Wire to the generator circuit so it comes on as the generator starts.
  • Install a non- return valve in the sea water inlet line, post the strainer, so the impeller stays wet.

Happy Generating.

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Old 03-07-2017, 05:59   #2
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Re: Kohler 5E/4EF 7.3E/6EF Generator Overheating Resolved

My Kohler 5E was shutting down after 6 or 7 minutes as well. It has about 200 hours on it.

I removed the heat exchanger and replaced the thermostat. But after I placed the old one in a pan and heated the water, I found it was opening around 190F as it should. I blew out the heat exchanger with an air hose from the exit end of the water connection and after much shaking and blowing - removed 21 pieces of rubber from old impellers that had failed.

I replaced the heat exchanger and it still overheated. Adding anti-freeze mixture via the cap on top of the unit didn't help. It was full but still overheated. Due to the installation in my Sea Ray 290 Sundancer, the overflow reservoir is difficult if not impossible to get to. So my solution was:

-remove the bleeder screw
-route a rubber hose into the opening and into a small funnel
-taped the funnel to the boat
-poured anti-freeze mixture in the funnel and squeezed the hose that exits at the far side of the cast iron reservoir that holds the heat exchanger
-the anti-freeze would "glug glug" slowly into the bleeder opening
-I added probably a quart of mixture this way refilling the funnel at least ten or twelve times
-finally it would take no more and just overflow out the radiator type pressure cap opening (which I left open during this process)
-I replaced the pressure cap and started the generator

It has run perfectly ever since!! I had been dealing with this issue all of last boating season and into the beginning of this one. I was beginning to think the internal pump of the engine had failed. But after reading so many forums, I found almost no one finding this to be the case. It was almost always a clogged heat exchanger, a failed thermostat, and most often - an air locked cooling system.

This method worked great for me with the least amount of tools and aggravation. Hope it helps.


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Old 03-07-2017, 08:06   #3
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Re: Kohler 5E/4EF 7.3E/6EF Generator Overheating Resolved

Generators of course run at a steady RPM, for this reason it's easy to eliminate the rubber impeller pump and replace to with a 110VAC air conditioner pump.
That pump will run for thousands of hours without failure and cannot send rubber bits into the heat exchanger, it also has the advantage of not being able to flood the engine with water from excessive cranking, as it's not running until the generator is making power, which doesn't happen until right at operating RPM.
I removed mine after the seals went bad, spraying salt water all in the generator enclosure, but of course I didn't know that.
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Old 04-07-2017, 05:33   #4
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Re: Kohler 5E/4EF 7.3E/6EF Generator Overheating Resolved

Greetings and welcome aboard the CF, LearDriver.
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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