All:
Yesterday I wrote of my problems with Miss Molly winking at me with her
oil pressure light. I received several suggestions as to what might be
the problem; I send a big "Thank You!" to everyone that offered advice.
Here's the background:
Last year I rebuilt Molly's engine. Had problems with the light
flickering then, so I replaced the oil pump (needed it anyway) and the
bypass spring. Put her away for the winter; didn't drive her long enough
to get the engine thoroughly hot (read an hour or more). She has about
2500 miles on the rebuilt engine.
This year I have driven her several times and had no repeats of the
problems until yesterday, which was the first time I have driven her for
an extended time (more than an hour) in temps above 60 degrees. I have
also recently installed a T-fitting to run both the oil light and a
mechanical guage, the guage is accurate. The thermostat is rated at 190
degrees, and I live in SW Iowa.
I do not have an oil cooler installed; while it's on my wish list, it
won't happen anytime soon.
The oil level is correct and is Castrol GTX 20W50. The filter is also
new as from the time of the rebuild, I changed oil and filter at 500,
1000, and 2000 miles. I use a standard Fram replacement filter (on all
my hobby cars I have a habit of changing the oil and filter every 2000
miles after the break-in period, while also changing the filter halfway
between oil changes). Oil pressure has been 75 pounds at idle on a cold
engine, and 40 pounds on a warm engine.
Yesterday afternoon, after a couple of hours of on/off driving in 70
degree heat, the pressure dropped to 25-30 and the light flickered and
then came on at an idle of approximately 1000 RPMs. The light went off
as soon as I tapped the throttle and it came above 1400 RPMs. The temp
guage was reading 190 degrees but shot up to 220 degrees when I shut her
down. No evidence or sign of overheating.
Last night, in 50 degree temps, the light began flickering as soon as the
engine reached 190 degrees (within ten minutes of being started). The
oil pressure guage was reading 40 lbs. Pressure did not drop below 40
lbs at idle but the light would still come on, and go out when I
increased the RPMs and the pressure went above 45 lbs.
I am reasoning that my problem is a compendium of three things:
* Too high a rating on the thermostat: I think I should change down to a
165 degree one to reduce the oil thinning at the higher temperature.
* A bad oil pressure sending unit. I am seeing some oil leakage around
the plastic portion of the fitting. I think I'll try replacing it with a
Chevy six cylinder one, as the threads are the same, and I think they are
rated the same.
* Bleeding off of pressure at the valve train. I thought I was picking
up a bit more valve noise than initially, so I plan to readjust the valve
clearance back to 0.010 (as suggested by Bob Howard and Dave Ramsey), as
I haven't done that since the rebuild (guess I got too used to hydraulic
lifters).
What is the correct / normal oil pressure on the 1500 engine?
Anyone have any suggestions, care to call me an idiot, or offer any other
critiques or advice?
Rich
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