FWC intermittent overheat

[zialater]

Howdy Afourians,

My problem began a couple of weeks ago. I have FWC and about 4 months back I removed the t-stat and installed a moyer bypass valve. That brought my temp down about 20 degrees to 150-160 range and things were great. But in the last few weeks she would occasionally start running up into the 200+ range. But then about half the time, it runs up to 160-180 and remains there. BTW i have checked the temp gauge with an IR thermometer (great gadget) and it's pretty accurate.

The raw water side seems to be fine - impeller - flow output - batching - filter - all working as they should.

So, I just replaced the FWC impeller - it was due anyway but there were no vanes missing - in other words - no smoking gun there, darn. The heat exchanger might be the issue but i did a remove and clean about 2 years ago on it. I can feel the cool side where the raw water comes in but as i feel down lower on the exchanger it gets warm about 3/4 of the way up - see pic. Does that sound normal? I am guessing that removal and cleaning it is my next move. But the fact that sometimes it runs at a normal temp is puzzling.


Also - i use green prestone 50/50 diluted antifreeze - this was what the PO used.

I have played with the bypass valve but it does not seem to have much effect - i usually leave it at 45 degrees.

Any thoughts on a miracle cure would really be welcome! Hahaha, OK maybe a miracle cure is asking a bit much. Any thoughts on my next moves?

Sincerely,

Joe
C&C 30 MK1 "Zia"

[ndutton]

Back to basics

The overheating is virtually always a matter of flow, in your case in either the raw water or coolant circuits or both. The question then is how to determine which or decide who cares, I'm going for the full Monty.

Quantitative observations are difficult and therefore unreliable unless they are extreme. The raw water discharge may seem fine, as it has always been but can you really discern between 20 batches per minute and 15? Throw in variations in RPM and the casual observation isn't a great diagnostic tool. The coolant circuit is even harder because there's no visual to observe in normal operation.

I hate problems so I would go the full Monty but that's my dementia. I'd giver her an acid flush in both circuits, disassemble and roto-rooter the HX tubes, remove the engine side cover to inspect and muck out the water jacket, replace the cover with studs, replace both impellers and add M7 cam shoes, check the exhaust mixer. There, that oughta do it.

For a less aggressive approach, measuring the in and out raw water and coolant temps at the HX with a gun may indicate compromised flow within. In each case you're looking for a significant change in temps of in vs. out. I can't tell you what temps to expect, just the greater the difference the better. Looking inside the coolant reservoir (cap removed) with the engine running should indicate flow but we're back to how much is enough? When was the last time the coolant level was checked?

The intermittent nature suggests a migrating blockage.

[hanleyclifford]

When you removed the thermostat your coolant suddenly found itself able to run thru the block at a much faster rate. Small chips of metal could have gotten on board for the ride, but got hung up in the exchanger. I agree that cleaning the exchanger should be the first step. FWIW, I keep a strainer in the antifreeze loop just before the pump where the antifreeze is coolest.

[Al Schober]

I've got the Moyer fresh water cooling, no thermostat, and the coolant temperature only gets up to 120F if I'm pushing hard. I moved my coolant temp sensor from the head to a tee on the manifold outlet. Doing a full cleanout of the HX may be more than it needs, but at least you'll only have to do it once. Sometimes you gotta bite the bullet..

Hanley: great idea on the strainer. Any idea what strainer you used? Got a picture?

[romantic comedy]

curious as to why you removed the thermostat. Was it running hot?

[zialater]

Yes she was drifting up to 180 - 190. so I removed the Tstat and put in the bypass - she went right down to 150 -160.

[hanleyclifford]

I've got the Moyer fresh water cooling, no thermostat, and the coolant temperature only gets up to 120F if I'm pushing hard. I moved my coolant temp sensor from the head to a tee on the manifold outlet. Doing a full cleanout of the HX may be more than it needs, but at least you'll only have to do it once. Sometimes you gotta bite the bullet..

Hanley: great idea on the strainer. Any idea what strainer you used? Got a picture?

Nothing fancy, Al - just the garden variety Jabsco with a fine mesh as for a water puppy:http://www.moyermarine.com/forums/at...8&d=1438196341

[zialater]

Final update on my intermittent overheat (success!)

Thanks for all the good ideas/advice.

After the response from my first post, I disassembled the HX and found (what i thought was a smoking gun) some gunk in the raw water side - it looked like coagulated mud. I cleaned it out with a hose and the HX is nice and clean on both sides. Upon reinstall the overheat problem was still with me albeit somewhat less severe.

Next was a hose flush thru the FWC from both the manifold (front to back) and then from the coolant pump in and out the back of the manifold. A little gunk but not really much -and the overheat was still with me. The water ran thru the system and came out in a strong stream.

Finally - I bit the bullet and did a FWC acid flush - in thru the FWC pump and out through the back of the manifold into a 5 gallon bucket. I used 30% muriatic acid in about 4 gallons of water. Amazing black gunk came pouring out into my catch bucket. I left it in for 12 minutes (since it was a heavier concentration of acid) and then flushed for 15 minutes with fresh hose water.

That did it and the engine is now running all day around 150 - less if I close the bypass valve.

I am writing this up for any listers who think (as I did) that an FWC system is closed and does not need an occasional acid flush.

I hope this helps the next sailor who searches the forum for FWC acid flush - it's easier than it sounds although that acid is pretty nasty stuff (gloves - eye protection - watch out for the fumes too).

Cheers mates and thanks again.

Joe