Steve,
First off... you should be using a 15W-40 minimum even on a new engine. The
original 1962 TR4 owners book called for 20W-40 (The TR4 engine is the same in
every respect for this discussion). If the engine is along in miles... 20W50
makes more sense.
Normal behavior on a new engine running 20W-50 with the engine warmed up...
should be 70lbs at speed and about 45-50 at idle. That same engine at full
hot on 10W-30 might drop slightly below 70lbs at speed and get down to 35-40
at idle.
I experienced the same thing you did when I bought my car. The oil pressure
was like yours and the oil was old so I changed to 10W-30 Mobil-1 and a new
filter. The oil pressure was OK at cold start but went south just like yours
when I it warmed up and even worse have a long drive at speed.
I ended up rebuilding the engine and found the rod bearings to be badly worn
and the oil pump was worn to out-of-spec. There were other issues that added
up to a rebuild. If I had not rebuilt it... I would have used 20W-50 and
milked for as long a I could.
The other issue here is the oil pressure limit switch. If the spring is
broken or limp... the valve will kick in too early... before 70. A reasonable
test is after changing to 20W-50... on a cool morning the first oil reading
should be about 70lbs. If not the spring may need replacing or the adjustment
nut might need a couple of flats towaed tightening.
Hope this helps
Brian Sanborn
62 TR4 CT16260L soon to be "O" - Groton, MA
My TR4 Restoration Web Site
http://www.net1plus.com/users/sanborn
E-Mail: sanborn@net1plus.com
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