What Is This Goo?

[Delancey]

Tearing apart the old engine. This jelly-like goo was in the top of the thermostat. What is it?

[deckofficer]

My guess if it is a closed loop cooling system and you run a water/antifreeze mix, just maybe over time you mixed OAT antifreeze with Ethylene-Glycol antifreeze. This creates a slimy, gel like goo.

[Delancey]

Thirty year old boat, have owned it for about three years. Universal 44hp. Can't say the PO was big on maintenance. You might notice I broke the bolts off when I removed the cover. Repowering, so fun tearing it down knowing I don't have to fix broken bolts.

Regarding the goo, can't say about OAT antifreeze. Who knows? My impression of the PO is that anything is possible.

[leftbrainstuff]

Could also be from a 'miracle' leak sealer. Are you repowering because of a related issue?

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[atoll]

my guess would be aluminium oxide ,brass thermostat in an aluminium housing casing eletrolysis,look for pitting in the top cover

[Delancey]

Spot on with that assessment my friend. I wasn't paying attention but you can see the white aluminum oxide on the face, hence the broken bolts. Doubtful the cover has ever been removed.

I notice the goo is on the non-flow side. Suppose that is a factor in its accumulation as this sort of concentrated jelly? Does it affect the performance of the thermostat?

[atoll]

Originally Posted by Delancey

Spot on with that assessment my friend. I wasn't paying attention but you can see the white aluminum oxide on the face, hence the broken bolts. Doubtful the cover has ever been removed.

I notice the goo is on the non-flow side. Suppose that is a factor in its accumulation as this sort of concentrated jelly? Does it affect the performance of the thermostat?

I would think if the engine was running regularly the oxide would not be a problem.

problem comes when the engine stands without running,oxide should dissolve once there is a bit of flow if it is still "jelly" like.

seen this many times on outboards,where the cooling galleries have become totally blocked by oxide and salt which will quickly overheat an engine.

the oxide crystalises if it dries out and becomes hard but should stay soluable in liquid