When you have an engine that old, that's done a lot of sitting, you get all kind of issues, especially with rubber items and corrosion internally. If not the water pump, you might have a lifter sticking a bit then frees up after it gets more oil pressure. I agree with the moderator I would use 10-30 not 40 weight. I was able to permanently cure this exact problem with a can of Lenckite poured in with the engine cold. Lenckite has in it some ether, which is one of the best cleaner/solvents known. You can get the same product under the label Avblend that is FAA approved for aircraft engines. Ether evaporates very quickly with heat, so the product must be added to the oil with the engine cold and then start the engine right away. The ether dissolves the varnish deposits and breaks down any bits of carbon that could be hanging up the lifter. I don't generally advise oil additives but this is one that works as intended. Of course after you run the engine for 5 -10 minutes drain the oil and put in new. The old oil will come out very black from the dissolved junk.
Retired Anesthetist. LTP. Pilot with mechanic/inspection ratings. Between rigs right now.. Wife and daughter. Four cats which we must obey.
