Stuck thermostat cover

Hello all,
I’m rebuilding a 1983 evinrude 9.9 and am currently disassembling the power head. I have what appears to be a stuck thermostat cover on my cylinder head. I’ve soaked the gasket in penetrating oil for days, even tried a wood dowel and a hammer to see if I could shock it loose. Any ideas from the collective on this? The cylinder head is toast and I have a replacement on order, but I need to reuse the cover.
Thanks much,
Lucas

Heat hammer? Heat ... cool, thermal shock ... whack bolt with hammer to loosen the threads.

Some heat from a heat gun or propane torch should help things along.

Don't be tempted to pry it up with a screwdriver, cast aluminum is pretty easy to break.

Is it stuck on a stud, or is it just stuck by the gasket?

MrGiggles said:

Some heat from a heat gun or propane torch should help things along.

Don't be tempted to pry it up with a screwdriver, cast aluminum is pretty easy to break.

Is it stuck on a stud, or is it just stuck by the gasket?

Click to expand...

Screwdriver is a solid no.

A scraper on the other hand worked carefully around the edge will split a stuck gasket.

A utiltity blade, handle with care, use gloves. Better yet hold it with pinch nose pliers. Tap gently into joint.

Razor blade with a hammer got it done! Thank you all.