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89 chevy k1500 v 350 motor oil pressure jumpping around irraticaLLY.

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5 years 1 week ago #27914 by wacoeagle
OK this is just a foollow up, the old pressure sensor located above the oil filter, was reading abt 23 to 25, then jumping around like crazy with revving or decellerating of the engine. it never climbed much past 30. I replaced it and now oil pressure is around 30 psi at idle , very steady, and climbs to around 70 with a throttle snap.
I cut open the old sensor, it is basically a potentiometer with a lever assembly that moves back and forth with pressure, and varies the voltage signal.
my sensor was gooked up with thick tarry oil., and the electrical connector that sits inside was not making good contact, because it was rusty inside.
I wonder how it actually functioned at all. it also looked to have a small leak around the seam of the top of it. im happy to know I now have a correct oil pressure reading, and my engine is in good shape according to my pressure readings. (my other 350 reads abt 35 at idle). on cold start up.
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5 years 1 week ago #27916 by Dylan
Thx for the follow up! I'm moving your post to the repair section ;)
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5 years 1 week ago #27960 by Andy.MacFadyen
Good job I have never taken the gauge sensor type apart for an autopsy, but I have cut the on/off oil pressure switches open they are just a diaphragm and a ball bearing as spring loaded contact. With oil pressure switches and sensors weeping round the rim is probably enough to justify going straight for a parts swap after doing a quick by-pass and supply volts test on the wire.

I did toy with the idea of buying a cheap oil pressure test gauge set but these days low oil pressure issues are almost unheard of. It was different 40 years back an oil pressure lights glowing at idle was not that unusual on high milers, quite often if an oil change with good old 20w-50 didn't work we used to fit a lower pressure switch to stop the owner worrying too much, the engine was knackered anyway so Why Worry Be Happy .

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



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5 years 1 week ago #27961 by wacoeagle
I have a strong 350 in my 94 and put some leftover 20w50 in it. I got abt 1/2 mile down the road and it blew one of the spark plugs out, not the threads, but the ceramic part. She like the valvoline 10 w30 so thats what ive been running.

the 89 I did the head job and top gasket set on had a bad blown head gasket, Ive replaced the oil 3 times, and the filter. I cut the filter open and look at it.. its amazing how much residual gunk remains in an engine after head gasket failure. oil pressure is now holding at 40 psi at a cold idle, and engine sounds very good.
I will have over 100.00 in oil and filter changes in it by the time im done, but its too much work to take a chance. I know once these 350s are right they can run a very long time without major issues.
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4 years 11 months ago - 4 years 11 months ago #28846 by Andy.MacFadyen
I have seen the creamic blow out on a couple ofspark plugs one was a Hitachi I can't remember what the other one was in both cases manufacruring defects on brand new plugs .

Valvoline make good mineral oils this is tradditionally because the raw feed stock available to US specialist lubrication oil producers came from the Gulf of Mexico and had built in multi-grade viscosity characteristics without additional additives -- North Sea oil has similar properties.

20w-50 oil was the first multigrade oil to hit the market around the late 1950's early 1960's it was essentially a straight SAE 30 grade oil with a minimal ammout of additives. The problem with additives is after 5,000 miles or so they become exhausted.

The best synthetic oils have almost zero addtives as they are naturally multi-grade and naturally detergent and don't breakdown to anything like the same extent under intense heat so the engine and the oil stays cleaner. Unless the engine is already internally dirty you might want to consider using a 10w-40 or better 5w-40 as these grades will give more constant oil pressure from cold winter through hot traffic jam conditions. Even cheap suppmarket synthetics are good deal better than any straight mineral oil ---- I must add a rider to that no quality mineral oil sold these days dosen't have some synthetic in the blend and 98% of fully synthetic oils contain some mineral oil.

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



Last edit: 4 years 11 months ago by Andy.MacFadyen.
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