Oil pressure too high?

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1974DartSwinger

1974DartSwinger

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Ok, so the weirdest thing happened tonight. Well, ok maybe not THE weirdest but it has gotten me thinking and can't figure it out. . .

Driving my '66 Cuda with a 1974 stock 360 4bbl in it. I've put about 4,000 miles on it so far this summer, changed the oil and filter maybe 800 miles ago. Used my good trusty Rotella 10-40. Have had no problems at all ever before.

Went out for a drive tonight. Usually the oil pressure is a little over the "half way mark" on the gauge when its cold at idle but then drops down to just below the half way mark. As she warms up at cruise, 50mpg 2,000rpm it sits right about the 3/4 mark, it has never gotten above that unless I'm on the highway going 70 or 75. Ok, getting a little rambling, but it is 1am here and I had a final exam this morning ;)

Basically, when I went out for a drive tonight the oil pressure was staying in the high 3/4 tick area at idle after it was warmed up and just cruising around at 30-40mph it was pegged, the gauge was dam near maxed out! I dont really know whats going on. I figure too much oil pressure is better than none but Hmmm . . . at a couple lights it would get back into the "normal" range but as soon as the revs got over 1,000 pressure would be right back up there too high.

Before everyone says anything, yea I know 10-40 is a tad thick but its been above 70 here and I drop to thinner stuff when it cools off so I dont think it has anything to do with that, plus it was about 80 here today.

What the heck would cause the oil pressure to spike like that and stay spiked? For snickers I may drop the oil filter tomorrow and see if anything got stuck in it . . . or if some sludge broke loose? Thats about all I can think of, she runs like a top
any other ideas?
 
The gauge may have failed. Run a non-electric one to the port where the factory one screws in and see what it reads.
 
Yup. Verify the gage is accurate. Sounds more like a gage issue. Does it read differetly when the headlights are on? (no..seriously...lol)
 
Could be the gauge. Could be the sender. Also check the wire to the oil sender. It may be chaffed to ground ever so slightly and intermittently.
If the temp gauge goes up just a little higher than normal also,
the mechaical voltage limiter is at fault.
 
I'm going to order a new pressure sending switch just for the heck of it . . . theoretically if the switch is fine and the gauge is fine, what else could cause oil pressure to spike so high like this?


Could something I havent thought of cause it (something other than sludge or junk getting caught in a passage)

For the record, I'm pretty darn sure my gauge and switch are actually working fine. Maybe it would be a good idea to get an aftermarket oil pressure gauge to stash under the dash for a more accurate reading.
 
1974DartSwinger said:
I'm going to order a new pressure sending switch just for the heck of it . . . theoretically if the switch is fine and the gauge is fine, what else could cause oil pressure to spike so high like this?


Could something I havent thought of cause it (something other than sludge or junk getting caught in a passage)

For the record, I'm pretty darn sure my gauge and switch are actually working fine. Maybe it would be a good idea to get an aftermarket oil pressure gauge to stash under the dash for a more accurate reading.
Click to expand...

Your kidding, you trust factory electric gauges?? I have yet to see any be accurate unless they are sent off to a reputable gauge re-manufacturer and calibrated. The only thing that can cause excessively high oil pressure is the relief valve in the oil pump stuck. In nearly 30 yrs. of working on engines I have only seen one stick and that was in a Jeep. It's possible, but not very likely. The chance of a sending unit going bad is pretty high. I've replaced more of them that I can even remember. Sometimes your lucky to get a year or 2 out of them.
 
I've seen relief valves stuck but never intmitently. Always blows the oil filter leaving no question what the fault is.
 
is there any way to see if the relief valve is stuck? Or is that something you have to put in a new oil pump?

Out of curiosity what weight oil are you guys running? Do you think the 15-40 Rotella T is too thick for my 360? I've been using it since the diesel oil has the good additives for old school engines. I've ran it in my '71 Honda 750 motorcycle for 6 years after the rebuild and its great stuff.

(haha now I'm going to get all the oil science guys to reply)
 
I run 15/40 in my Neon, my truck, and a lot of customer engines. It's fine. The relief valve ona small block is up in the pump casting so you have to drop the pan and remove the pump to get to it. A stuck relief would blow the filter. I've over-shimmed a standard volume pump and gotten 120psi on a fresh engine before. But if it stuck you'd really know it. Get a cheapo mechanical gage and stick it on it to see what it's doing. If the system's fine, you can always go back to using the factory gage althought I probably wouldnt unless you had the gage fixed.
 
Ok, I'll see if I can borrow a friends or buy a cheap pressure gauge.
Couple follow up Qs:
-Can I hook up my multi-meter to the pressure sending unit and use a voltage reading to see if the sensor and/or factory gauge is bad? Anyone know the conversion or where I could find it for this?
-If I'm going to hook up an aftermarket oil pressure gauge where would be a good place to hook into an oil passage? Or is it best to just go where the factory sending unit plugs in?

Thanks a bunch guys!!
 
I had that happen once. Electric gauge, I don't remember exactly what was happening at the sending unit but it either had a bad connection or it was grounding out.

Whatever it was, I was expecting my oil pump to self destruct or other bad things to happen because it suddenly looked like my relief valve had stuck shut.
 
sorry for the hi-jack...... but diesel oil...? really? I thought it was bad to run for a prolong time? I Just used it once to break in the cam.
 
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