realized this is a better place to post. Generally, what causes lifter noise and why am i getting it only when the engine is hot after turning it off for a short time and restarting? In 5 or so min of restarting, it will go away again.

 

There are many reasons for "lifter noises". In your case it sounds like the lifters or lifter is leaking down when the oil gets hot and thins out. You didn't state the year and mileage of the engine. Actually the lifters don't make any noise the valve train makes the noise due to increased clearances, i.e. valve tap. The lifter is a piston inside a cylinder (the lifter body), with very tight and precision clearances. There are other components inside also, a check ball and spring and metering disk. The piston is trying to compress oil inside the lifter body and since it can't it acts like a solid lifter. The push rod bears on end of the piston like a connecting rod. If there is any excessive wear or dirt in the lifter the oil cushion tends to leak out --remember there is the constant pressure on the lifters internal piston from the valve spring via the pushrod. When the oil is hot and thin and if the conditions are right (due to wear or internal contamination ) the lifter tends to leak down, that is the oil cushion the piston is sitting on leaks out and the piston moves closer to bottoming out (collapsed). This leads to excessive valve to rocker arm clearances ( if the lifter preload is small this occurs with little leakdown) and valve clatter /tapping (lifter noise). There is also the metal expansion factor due to normal engine heat. When you restart the engine the lifter is pumped up again by the engine oil pressure via a hole in the lifter body and a check valve in the lifter. This is not instantaneous as the engine oil pressure is less that the valve spring pressure, so the engine clatters for a period of time, until the oil cushion in the lifter builds up again. The discussion above is a bit simplistic and there are other factors at work, but that is basically it.

 

Stractor, thank you for your reply, I feel like i have a pretty good understanding of the lifter issue.

A few things you said make me wonder if the 5w/30w oil the mechanic put in this old engine is part of the problem. I am getting strong oil pressure when the engine is cold, but when hot, pressure at idle drops to 22. I was disappointed when the 5/30 was put in this old engine , a 1975 300 inline six (i also have a 1975 amc 360 5.9 liter and he put the 5/30 in it too). Both are hunting buggies with high mileage and are used in moderate climates (florida). .

do you think the lifter chatter can be controlled or minimized with 15/40, since florida weather is moderate? Is it worth draining the new 5/30 oil to achieve this?

 

could be that parts and clearances have worn out a lil wider over the years... could try running 10w-40 first see if that helps...

do you know what you were running previously in there?

i dunno if your one of them people who do it themselfs or one who just takes it to the shop every time... thats why i ask..

 

"the 5w/30w oil the mechanic put in " --Well There's Your Problem------ Unless you live in the colder climates, that is wayyyy to thin for an older engine. In your case I would probably use 20-50w, In fact I have used 20-50 here in the northeast for several years but switched to 15-40 Delo 400 . The 20-50 is slightly too thick in the winters here but fine in the summers. In the summer my engine oil pressure drops to around 20 after the engine gets really hot ( on a 90+degree day ) but comes right back to 45. If the pressure never came back I would be a little worried. I have a 90 with 98K miles. For your type of usage even a straight 40W would work fine.

 

thats the same reason i run 20w-50 in my truck... well sorta.. during the summer the needle pretty much pegs the top side of my water temp gauge.. and i know theres nothing wrong with my cooling system.. think it all stems from that 3qt oil pan.. winters ill run 10w-40 cuz 20w-50's too thick to run then.. and also dont have a cooling problem in the winter... but during the summer it just gets that oil too hot and will thin it out to the consistency of water... so i run the 20w-50 to compensate for that..