Yanmar coolant change

Dougcole · Mar 24, 2014

Hey All,

I'm getting ready to do my first coolant change on my Yanmar 4LHA-STP motors. Shouldn't there be some sort of drain low in the block so I can get out all of the coolant? I can't find it and there is no mention of it (that I have seen) in the manual. I can pull a hose off of the HE, but that won't get all the old coolant out.

Anybody know where it is?

Thanks,
Doug

DavidM · Mar 24, 2014

I just did a coolant change on my Yanmar 6LY. You are right, there is no mention of a drain point in the service manual that I could find. But boatdiesel was helpful.

On mine there was a petcock on the main heat exchanger and one low on the starboard, aft side of the block. The one on the heat exchanger drained easily, but the one on the block was plugged with coolant residue and since it was hard to get to to clean out I ignored it. The gurus on boatdiesel said that the heat exchanger drain would get 80% of the coolant out- 4 out of 5 gallons. So that is what I did.

The heat exchanger drain on your 4LH should be obvious so if that is all you can find then like me you should be alright.

It will take a while to get all of the air out after you refill. I filled as much as I could, ran it at the dock until the coolant was warm and topped it up as well as the overflow tank. Then went out for a run. When I got back the overflow tank was half full and when I removed the cap there was coolant up to the top, so it was good and full.

David

Dougcole · Mar 24, 2014

Cool. Thanks for the help David, that all makes good sense to me. I really like your Pilot BTW, if we didn't need more space I would have seriously considered one.

Ski in NC · Mar 24, 2014

I know the 6LY has a drain cock on the flywheel housing right side down pretty low, about where fw hsg meets block. The 4LH might have the same. If it is clogged, ususally a blast from a garden hose or compressed air will get it.

FF · Mar 27, 2014

Since its important to get rid of all the old acidified coolant , it is worth the extra $10. or so to drain , fill with distilled water , run a couple of min and drain again.

ONLY use the type antifreez the mfg suggests (color specific , dont mix colors ), and if a SCA is required the test strips to set the mixture is at most big trick stops.

Earl34Mainship · Mar 27, 2014

I can add to what djmarand, David, Ski in NC, and FF have posted. I have a 6LYA-STP in my 34T and had the same question as Doug when I changed coolant last year. The "experts" were telling me that they only get 3.5 gal out of the 5 gal crankcase then they refill with new coolant. Not good enough! The drain on the port side is obvious, but thanks to Marc and Frank at MarinePro in Cocoa, they pointed out the other drain and I got 4.+ gal out of the engine. I then flushed twice with distilled water before adding 50/50 coolant. Attached are photos of the drain on the starboard side... It's just aft of the lube oil cooler, and your 4LHA may not have the second drain in the same location as the 6LYA, but as others have said, getting every bit of old coolant out is important. BTW - if you don't get the answer you're comfortable with, call Marc or Frank at MarinePro, Cocoa. PS... on the backside of this drain, there's a stub out where you can attach a 1/4" hose and drain into your catch can...

jimL · May 29, 2017

Earl and all,

I resurrected your post based on my search to change the coolant in my Yanmar 6LY engines (circa 2005, 370HP).

As I identified the petcocks correctly, I tried to loosen the black plastic petcock on the starboard side, just aft of the lube oil cooler.

When I tried to loosen I heard and felt a CRACK and using a mirror I discovered the black plastic knob cracked at the base.

Help! No coolant came out, so I stopped there. Does the black plastic knob affix itself to a valve or petcock that I can open using another tool?

On my port engine, I did see the same setup, and evidence the PO used needle nose plyers or something to open it. I am reluctant to try on the port engine until I have more information.

Looking at Earl’s pic above, I have the same setup. Just wondering how to open the petcock when the block knob completing breaks off? Is there another way?

Thanks for the assistance.

Jim

Comodave · May 29, 2017

Not exactly to topic, but what is everyone doing to dispose of the old coolant?

Earl34Mainship · May 29, 2017

jimL said:
Earl and all,

I resurrected your post based on my search to change the coolant in my Yanmar 6LY engines (circa 2005, 370HP).

As I identified the petcocks correctly, I tried to loosen the black plastic petcock on the starboard side, just aft of the lube oil cooler.

When I tried to loosen I heard and felt a CRACK and using a mirror I discovered the black plastic knob cracked at the base.

Help! No coolant came out, so I stopped there. Does the black plastic knob affix itself to a valve or petcock that I can open using another tool?

On my port engine, I did see the same setup, and evidence the PO used needle nose plyers or something to open it. I am reluctant to try on the port engine until I have more information.

Looking at Earl’s pic above, I have the same setup. Just wondering how to open the petcock when the block knob completing breaks off? Is there another way?

Thanks for the assistance.

Jim

Jim... I wish I could help a fellow Mainship/Yanmar Bud, but I sold my 34 late last year and it's been a while since I changed coolant in he 370... The current owners are off to conquer the Great loop and enjoying their 34 foot treasure.... if I remember correctly, when I loosened the cap, the cap did not unscrew completely, but the coolant drained... So if the plastic cap is broken, the metal piece that connects the cap to the block may be replaceable which would give you a new (uncracked) cap. I relied on MarinePro in Cocoa, FL for answers to questions like this, and Frank (owner) was very wiling to assist.. Good luck with your project and Happy Mainshipping.. Earl

FF · May 30, 2017

As coolant may also be in other places , like a heater or water heater loop it is worthwhile to use a shop vac to blow into the fill to help the last bit to depart

jimL · May 30, 2017

Thanks Earl, I'm hoping other Yanmar owners will chime in about their experience with the black plastic petcock in the pic above.

Jim

Cigatoo · May 31, 2017

The petcocks on my 4lh are / were black plastic and broke also. Your Yanmar dealer will have replacements. Just put a wrench on the peacock and turn the whole assembly out. These are BSP threads so take note if sourcing from somewhere outside the dealer. Also take note that the replacements appear to be brass. The brass will tend to corrode on the salt water side so keep an eye on them.

jimL · Jul 24, 2017

This turned out more than I expected. When we went to remove the petcock it broke off with the threads still seated inside the engine. 4 hours later with the help of someone smarter than I we're in business.

The lesson here is to be careful about over torquing a component off, or it might break. I loosened (and tightened) the other petcock on the port engine so I shouldn't have the same experience.

We replaced the coolant and all is well.

Thanks for the assistance and the reference to the Cocoa, FL yard that came through with the part.

Jim

Yanmar coolant change

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