very hot very quick...

[anglosax]

Like radience91 post , this A4 has recently installed FWC and after 10 hours or so, running at 170-180 under normal cruising conditions, developed a severe overheat. We checked all hoses, the Holley t/stat, the coolant pump and the raw water circuit and all seemed ok but the overheat persisted. There was good raw water cooling stream out the exhaust but it went from stone cold to 225 and boiling in 3-4 minutes under load.
FUrther investigation of the heat exchanger[vertical type] and the lower hose coolant return line found them blocked with a scale type debris that lodged in the lower section of the heat exchanger and the return hose and fittings. It even blocked the return port of the coolant pump effectively stopping coolant flow back to the engine.
I have not seen this before with any A4, although FWC conversions are rare,does anyone know what causes this scale build up and what to do to prevent it in the future. FYI coolant was 50/50 antifreeze & water
Thanks

[rigspelt]

... this A4 has recently installed FWC and after 10 hours or so, running at 170-180 under normal cruising conditions, developed a severe overheat. ... Further investigation of the heat exchanger[vertical type] and the lower hose coolant return line found them blocked with a scale type debris that lodged in the lower section of the heat exchanger and the return hose and fittings. ... effectively stopping coolant flow back to the engine.
... does anyone know what causes this scale build up and what to do to prevent it in the future.

Scale present in the engine before the FWC kit was installed? I did a descaling/flushing prior to installing FWC on our A4.

[hanleyclifford]

You are in effect flushing the block but the debris lands in the exchanger. The remedy is to flush the block with outlet disconnected and thermostat removed. When you re-activate the antifreeze loop put a Jabsco style strainer just ahead of the antifreeze pump inlet temporarily and observe what accumulates. When you have achieved normal clean flow and 180 degree running (or cooler) remove the strainer and replace the thermostat.

[anglosax]

scale?

Thanks for the suggestions - I did a flush before the conversion but the amount of scale found now leads me to think something else is going on - however I will put a strainer in the system and see what happens next

[Bold Rascal]

Just had the same experience

Do yourself a favor and check for debris/scale blockage at the "out" fitting on the exhaust manifold. I did this innitially and thought all was well yet still overheated immediattely. I then actually removed the fitting from the manifold and found the blockage within the manifold itself.

Don't know what type of heat exchanger you have but you should be able to observe coolant flow at the fill cap.

[anglosax]

some like it hot...

Update - I found even more debris scale at the inlet of the HX but the manifold was clear at both ends. The scale is very interesting in as much as it appears to be layered around the inside of the coolant hoses and seems to have deen deposited in layers, some dull yellow but predominantly black. The hoses are standard black Goodyear heater hose and were new at conversion. There is a good handfull of scale out of the hoses - they are each 5 ft long as the HX is remote from the engine - it is definately not rust/carbon scale from the block - more like some wierd chemical deposit out of the coolant
[Does Anybody know what happens if you mix antifreeze with muriatic acid??]
With full circulation now restored the operating temp is back to 150-160
GO FIGURE!!!!

[edwardc]

... it is definately not rust/carbon scale from the block - more like some wierd chemical deposit out of the coolant...

Probably the organic "sludge" that accumulates on all surfaces of the cooling jacket as microscopic marine organisms get killed and cooked by the engine heat. It looks like black grease. It's really hard to get all this out with just flushing, even with acid.

One mechanic told me I'd be wasting my time converting an old raw-water cooled engine to FWC unless I thoroughly cleaned out all of the cooling jacket, preferably by hot-tanking the block! I found this position a little extreme, but the principle is sound.

I imagine over time that less and less will "plate out" in your new hoses and HX until the chemistry of the anti-freeze coolant stabilizes at a new equilibrium.

[ILikeRust]

One mechanic told me I'd be wasting my time converting an old raw-water cooled engine to FWC unless I thoroughly cleaned out all of the cooling jacket

Makes sense to me, considering the amount of sludge, crust, and crud I found in my engine. It's a 1983 engine, installed in 1983, run on raw water cooling in the Chesapeake Bay.

I am converting to FWC, but I spent literally a couple hours cleaning the block, head and manifold, inside and out. I cleaned the heck out of the water jacket and got a pretty impressive amount of crap out of it.

Which makes me feel pretty good about switching to FWC. It should have a good flow all around... I'm hoping.

[anglosax]

but I prefer it cool

I think and hope you are correct and I hope this adventure can help some other poor A4 owner tearing his hair out in frustration.
Just when you think youve seen it all.......

[anglosax]

huh?

"until the chemistry of the anti-freeze coolant stabilizes at a new equilibrium."
Ed - thats a $20 sentence if ever I saw one !!!!where do I send the check?

[edwardc]

"until the chemistry of the anti-freeze coolant stabilizes at a new equilibrium."
Ed - thats a $20 sentence if ever I saw one !!!!where do I send the check?

Sorry. I think I need to go sailing more!

With that in mind, I blew off bleach-treating my water tanks today and took the boat out instead.

[Dana Mace]

Scale present in the engine before the FWC kit was installed? I did a descaling/flushing prior to installing FWC on our A4.

Installed FWC in my 1976 allways raw water C&C 27 and for a whole season filled a strainer with rusty crud. I still have the strainer as I have had problems with my adjustable indigo thermostat of which Tom has since changed to a different device (thanks) and wants another $80.