fresh water cooled A4 overheating

[tombrcc]

While motoring home today, after 2 hours of perfect 180 temp my A4 overheated. Got a tow back then let the engine cool for a good 5 hours. Block was at same temp as surroundings. Restarted and she ran just like before but temp quickly reached 180 and passed.

I checked fresh water side of my heat exchanger and it was room temp, not even the slightest bit warm. My raw water pump is moving plenty of water. I inspected my fresh water impeller and all looks good. I'm by myself so don't want to pull outlet hose, takes too long to get from cockpit to cabin and back.

So, I'm thinking this is either a pump failure, thermostat or clog. Any advice on further troubleshooting? Plan to pull and test thermostat tomorrow. What throws me off is how cool the heat exchanger was, I figured it would be a little warm but I'm new to working on these.

Any advice is appreciated.

[Marian Claire]

With the engine cold. Remove the fill cap of the HX and start the engine. You should be able to visually check for movement/flow of the antifreeze.
I think someone recently posted about a pump where the impeller sheared of the shaft. Looked OK but was not pumping at all. If you have the T-stat out you could try running the engine with it removed just as a check. Seems to me that if the FW pump is shot there would be no flow of "hot" coolant to/thru the HX and with full raw water flow passing thru the HX the HX would stay at the ambient temperature of the water the boat is sitting in.
Dan
S/V Marian Claire

[edwardc]

I agree. You most likely have a clog in the coolant loop. If the thermostat was stuck, you'd still be getting some heat in the HX from the manifold. The most frequent clog sites are any elbows in the plumbing. Try the fitting at the exit of the manifold first, as it will tend to catch any crud or flakes of rust that come from either the Block or the manifold.

[tombrcc]

Thanks for the suggestions, I'm going to pull the impeller and check for clogs when I run over tonight.

Separate issue, do either of you (are anyone else for that matter) know what size hose to get for connecting up the overflow container? Got damaged and would like to replace it.

[tombrcc]

After some troubleshooting I determined that the fresh water side of my HX is clogged and causing my engine to overheat. Pulled the outlet hose at the bottom of the HX and no antifreeze came out. I placed the hose in a gallon of water and opened the outlet side of fresh water pump, water flowed as expected. Fresh water side of HX is completely full of antifreeze. Also pulled the thermostat, tested in water @ 160-180 and worked fine. Ran engine with no thermostat and still overheated just to finally ensure it wasn't there.

I plan to pull the HX out tonight and give it a good cleaning. Everything I've been able to find online address clogging on the raw water side and not much on the fresh side. Any recommendations on what I should do here? What chemicals/cleaning solutions would be best?

[joe_db]

http://www.moyermarineforum.com/forums/showthread.php?t=11073&highlight=heat+exchanger

[Al Schober]

Glycol should be on the 'outside' of the HX, and should be fine. Raw water (sea water) runs through the tubes, and these are accessible for cleaning after removing the end caps.
Cleaning method is 'whatever it takes'. I've worked on one where the initial tool was a long (special order) drill bit. After that I used a wire brush like used for cleaning gun barrels.

[indigo]

Antifreeze Side Blockage

I have seen several cases over the years wherein the small spaces (.040" wide) between tubes on the antifreeze side of the HX become blocked with accumulated debris that has come out of the block/head/manifold. The area where this occurs is typically at the top of tube bundle where the antifreeze leaves the horizontal leg at the top. Removing the HX, turning it upside down, and back flushing it with just water via the normal bottom discharge port normally cleans it out. You should do this over some sort of container so you can see what flushes out. Often it looks like sand.

Tom

[tombrcc]

Thanks for the help. I've pulled the HX and taking it home to flush. How much antifreeze will ki need to refill the system? I have a water heater mounted about 5 feet forward the engine.