R. Riggs writes:
>> Does anyone out there definitely *know* that readings on the pressure
>> gauge of 10 to 20psi when hot at 800 rpm idle are dangerous? My
>> experience says they aren't.
> I drove my TR6 several thousand miles with (hot) 10 psi @ idle and 30 psi @
> 2K. The bearings were all worn when I rebuilt the motor, but no damage had
> been done, and it didn't require much machining. I think as long as you
> keep a tired engine cool and don't push it hard, it'll last quite a while
> (IMHO).
I think we need to define the word "dangerous" here. Webster defines
the root word danger as: "1. Exposure or vulnerability to harm or risk."
IMHO, low oil pressure readings are "risky". The top end of the motor
(in the TR6's case) is the last to receive lubrication. Low oil
pressure means that either the bearings in the low-end are well loved,
or the oil pump is giving up the ghost. (or there is a clogged
passage, or even a bad oil pressure gauge, or something else I'm not
thinking about!) Either way, the rocker shaft is going to suffer.
If the bearings are worn (most likely case wrt low oil pressure), oil
slops out the sides of the big ends of the connecting rods and dumps
back into the pan, never reaching other points of the engine. Low oil
pressure is not good.
I've read in some manuals that replacing the connecting rod bearings
every 50,000 miles is routine maintenance! (Haynes I believe) I find
this a bit extreme, but it will save machining the crank, and really
isn't that difficult a job on a TR6.
My oil pressure on my 6 was less than 15 when I completely rebuilt the
engine. The bearings had worn through to the copper, and it was time.
I had to machine the crank. Maybe it was past time.
Low oil pressure is dangerous. But it isn't catastrophic. (" 1. A
great and sudden calamity; disaster.") If you have 10-20psi at idle
oil pressure, and you're running 5W30, then yeah, no big deal. But if
you have 10-20psi and there's a fresh batch of 20W50 in there, time to
tear it down. But if you don't rebuild it then, I doubt that your
engine will explode into a puff of smoke. It'll just need a little
more machining when it's time to do the rebuild. (no big deal really :-)
Using low oil pressure isn't enough to decide when it's time to
rebuild an engine. That is a personal decision that takes in many
factors. I rebuilt mine because I was planning on running my car for
another 20 years. (It's for sale now. :-)
Cheers,
-Scotty
'75 TR6 (for sale!)
'70 TR6 (TBR - to be restored)
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