I just aqquired an '83 supra. The 5mge sounds good except when I start it up there's some audible scrapey chatter for just a moment and them it sounds fine. Also the oil pressure guage never goes over 50% (also Ive never taken it over 4KRPM) and reads about 10-15% when warmed up in idle. Honestly Im not sure if its getting bad pressure, a bad guage or sensor, or if the 5mge is just supposed to be a low pressure oil system...
I've read that theres alot of quirks with the oil pump/pressure on this engine and Toyota didn't fix it until 84, when they put in a better pump and a bigger oil pan to accomodate.
My question is should I try and replace with some kind of stock pump or is there something that works better if this really is a common 5mge quirk?

Is the chattering sound coming from the engine or the transmition? When I had my 85 supra, I had the same issue. The oil pressure always seems to go up and down every now and then. I replaced it and other related parts. Still the same... So, I left it alone. But when I raced the car it'll show a high pressure. And at idle it drops.

IR

Sorry it took half a year to reply...
I ended up getting about 3-4k out of that engine before it threw a rod at 233K. Since then I've had a remanufactured Jasper 5mge installed. It still makes this sound on startup! One mechanic told me that it was the oil pump and the delay getting oil up to the cams or valve train. Another told me it was probably a noisy starter motor.
Right now I'm at about 700 miles on the new engine, and breaking it in with 10w-30 dino juice. My next tactic is to switch to a 5w-40 synthetic oil and see if the ligther cold weight helps at all...

My '85 does the same thing. It only happens for about 2 seconds and then goes away. Usually happens longer in very cold weather.
Using lighter weight oil will let it get to the head faster but it will probably still "knock" on startup. I've tried differnt weights, brands, regular, synthetics, and it still occurs. Mine also has low oil pressure similar to how u described.

This message has been edited. Last edited by: un-naturally aspirated,