atomic 4 overheating problem

[cynthialee]

My Universal engine overheated due to a split hose. That in turn fried the impeller. I have replaced the impeller and water flow from the exhaust is just fine but the engine still overheats under load (does not overheat if idling). Any suggestions as to where start looking first? Any help would be appriciated. Alex from Toronto.

[Tom Robb]

Thermostat?

[sv Lorelei]

(This assumes a new style engine with the thermostat housing cast into the head. 1st make sure you're thermostat is opening. Run the engine at idle and watch for the dip in temp as you reach temp (somewhere between 140 and 160 F) where the thermostat opens. If the thermostat is opening there's a chance that the original overheating knocked a good amount of scale loose from the cooling passages in the head and block and a significant number of them may be pretty well clogged up. If that's the case, you can try doing an acid flush of the system and see if that helps though to be quite frank, I've done that and still found significant scale build up when I took the head off. If the thermostat isn't opening, replace the thermostat.

[holzbt]

Check the impeller you removed. If it doesn't have all the vanes still acounted for you can bet one of them is plugging up something downstream from the pump. The blockage might be passing enough water to cool at idle but not enough under a load.

[Mike Keers]

I agree with Holzbt. I owned an 'original' A4 for years (no FWC upgrade), and several times when impellers came apart I found rubber vanes blocking water passages. Mine had a short section of copper tubing that came off the pump, and if the impeller was missing any rubber, that was the first likely place to look, and I often found portions of vanes jammed in there. Once I went inside the crankcase side cover and found a large hunk of vane that had made it thru the copper tube blocking a passage in the block itself. Good place to start your diagnosis anyway.

[cynthialee]

Thanks for the help. Even though I have allready thought of most of the things that were suggested, at least I know that I am on the right track.

[Figment]

www.moyermarine.com/forums/ is the place to find this answer and more.

The A4 doesn't pass a great volume of water under the best of conditions. Before I started turning wrenches to look for blockages, I'd start with an acid flush. It's easy, it's cheap, and there is some likelihood that it will do the trick.

[Kevin G]

Try a reverse flush with a garden hose.

attach the hose to the back of the manifold and let it run thru the engine backwards. I did that with mine after I had taken the inspection plate etc off. I found about 3 inches of crud in the block, so I took that out by hand and then flushed it. It took a couple of flushes (but I'm used to that) because there was a piece of crud caught in a bend.

Simple engine, simple solutions.

Kevin g

[cynthialee]

thanks for all the help! I wound up installing the valva affair to divert more water to the engine from the bypass line. It worked!

thanks, Alex