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Dexcool or its equivalant is available everywhere. The Heat exchanger connects to the engine coolant crossover by two seals that are pressfit. If you are leaking coolant replace them and lube them with a silicone lube first.

Thanks for the help. Getting her out next week for a trip up to PIB!! See ya on the water.

Hey guys, I found the Prestone 50/50 pre-mix with DexCool at Autozone. Is this the stuff I want. I noticed it is already premixed, so should I buy the other stuff and mix it myself? Thanks

Quote:

Originally Posted by gcarter (Post 3084698)

While diluting the Dexcool is the way to do it, I would reccomend using reverse osmosis water, distilled water, or deionized water to dilute it with. Tap water is usually saturated with hardness minerals (calcium carbonate etc.) that scale the HE and the inside of the engine and reduces heat transfer.
I usually open the bottle of anti freeze and dump it into a 5 gallon bucket. Then I fill the the bottle with pure water and add it to the bucket. Mix thouroughly and use. If you're into the second bottle of anti freeze mix, put any excess back into the second bottle and keep it around to top up with.

Second the distilled water, never use tap unless in a pinch. Contains too many minerals that will leave deposits.

Leaking seals and closed cooling issues on Merc 496's

It appears that many Mercruiser 496's and Merc Racing engines with the front mount crossover closed cooling tanks can develop leaks in the rubber seals under the cooler from generally two reasons:

1.
The seals are getting old, have developed cracks or tears, or a moderate to severe overheat in the closed cooling system can cause these seals and end tank seals to develop leaks.

Solution:s The seals are relativly inexpensive and not to hard to change so change them carefully.
The older 2001-2003 Merc 496's tank band clamp systems were weak and not adjustable and would fail easily sometimes allowing the tanks to raise up and leak all or most of the dex-cool out.
(very serious issue and has genaded quite a few engines!)

If you have this early small fixed clamp system, take them off carefully and replace with newer stainless heavy duty band clamps with tightening screws.
DO NOT OVERTIGHTEN THE CLAMPS -DAMAGES SEALS AND TANKS!!

2. Storing these engines in winter in freezing or expremely cold temperatures, causes shrinkage in the rubber seals under the tanks and the coolant can and does many times leak into the bilge.
Suggestion: For these cold winter layups and storage drain the dex-cool level down just below the seal level and then refill to the proper fill point on resivoir in spring get ready refit and service. Be careful when refilling and servicing the closed cooling systems to use proper Dex-Cool at Merc recommended mixes. The seals unless to old or damaged should thaw out and be re-useable, however be careful and recheck coolant levels and for leaks and temperature problems on first startups and runs!

This seal leak issue is not really a part or engine issue as much as getting proper service and maintenance on the engines and doing the winter layups properly in the fall.

Hope this info and suggestions helps avoid leak problems especially for Merc 496 owners and gives you guys an idea of whats really happening to create the issue.

Best Regards,
Ray @ Raylar

Raylar, awesome post! Thanks for the info to all who helped. I got the boat out yesterday and added coolant and started up without any issues. I'll be taking her out next week.

Phil