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  1. #1

    Default Oil Pressure: Too high!

    I have a 1986 C10 with a 350 SB crate engine. One day the truck began to run very sluggish and I noticed the oil pressure was a little high. I stopped to check under the hood and discovered the oil was approximately one quart low. Very unusually for this truck! It does not burn, or leak any oil. It is garage kept, very well maintained, and driven less than 2000 miles a year for the past 4 years that I've owned it. Engine mileage is about 50,000. The previous owner who restored the truck kept it extremely well maintained also.

    I added one quart of oil to bring the level up to where it is suppose to be, started the truck and it was no longer sluggish since that time at all however, the oil pressure would sometimes be normal, and sometimes be a little too high. Over the next few days, the oil pressure began staying higher than what it is suppose to be for longer periods of time. Finally the oil pressure stays way too high all the time.

    I have not been driving the truck due to this problem. I have noticed that the valve cover gaskets are leaking oil now.

    Yesterday I replaced the oil pump (standard pressure and volume) and this made no difference in oil pressure. Today I removed the oil filter adapter and inspected it. The by-pass valve appears to be functioning properly, and the adapter was clean & free of any debris.

    When I removed the oil pan to replace the oil pump, I was kind of shocked as to how clean everything inside the oil pan and bottom end of the engine were. Everything still looked like brand-new condition! Not the slightest bit of dirt, sludge, or debris of any kind.

    This engine has regular oil and filter changes in spring and fall whether it's needed or not, and the oil that comes out at each change has always been very clean and no debris, metal shavings, etc. at all.

    I'm really stumped on what could be causing this high oil pressure problem. I know for sure that the pressure really is too high because I test it using mechanical oil pressure testing gauges. On one gauge that reads up to 50psi, the needle goes past the 50 and almost pegs out at the zero mark. On the gauge that reads out to 600psi, the oil pressure is right around 75psi.

    Any one else every encountered this problem? Or know what could be the cause of it?

  2. #2
    Jr. Apprentice smitht65's Avatar
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    it could be from using too thick of an oil , or possibly tolerances being too tight between reciprocating parts
    1977 Chevy Suburban K-20 4X4
    "MUD CHUKKER"

  3. #3
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    Welcome to the GM truck club 86. This is unusual to say the least. Since you know how to check oil press & where the press relief valve is, are able to change oil pump etc I'm guessing you are doing your own oil changes, so I won't suggest that some error prone mech. at the Jiffy Lube put 90 weight gear oil in your engine by accident.<-- Sounds funny but it HAS happened before.
    Replacing the oil pump would have taken care of the press relief spring/valve being stuck closed in the pump, so I would look at the bypass relief valve again. I know you have checked this also & it seemed free, but I would check the oil passage beyond the p.r.valve. Try blowing some compressed air into it and make sure the passage is not plugged. If the passage is free and clear, then the only other thing I can think of is that maybe one or two of the cam bearings have slipped and the oiling holes are not lined up any longer & might be causing the high oil pressure. One cam bearing oiling hole out of line with the block could cause 15-20% higher press, 2 out 30-40% etc.

    Whatever you find please repost because we are always interested to know how these mysteries turn out.
    Last edited by stephan; 10-27-2010 at 12:32 AM.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  4. #4

    Default

    Wow! I was just surfing the forums here and was surprised how fast I received responses to my post. This is a great forum!

    Hello smith 65 and stephan,

    The oil viscosity can be ruled out, I'm using 10w30, and as far as the tolerances being too tight, I really don't think that is the problem in my case.

    stephan: Yes, I do all my own mechanical work.

    "I would look at the bypass relief valve again. I know you have checked this also & it seemed free, but I would check the oil passage beyond the p.r.valve. Try blowing some compressed air into it and make sure the passage is not plugged."

    I will check the two passage in the oil filter adapter cavity tomorrow and let you know what I find. To do this compressed air test I am going to turn the compressor setting down to 45psi, and should I test both the inflow and outflow passages this way, or do the air test on just the outflow passage?

  5. #5
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    Ok I'm guessing here that the oil filter "adapter" that you are refering to has 2 lines comeing off the front of it and they go to an oil cooler in the front. If this is correct, that is not what I am talking about checking. Blowing air through there will only evacuate the oil out of the oil cooler. I don't think your cooler is blocked with the good service this vehicle has gotten & even if it was it would not cause this kind of pressure increase. Go back to the oil pressure bypass relief valve that you checked before, and blow the air pressure in there (35psi would be plenty) and see if the passage beyond the valve is clear. Use a small piece of rubber hose/fuel line on the end of your air gun to make it easier to seal to the valve. If you can't get air to pass that point, then something is blocking it.
    From the service history that you relate from you & the previous owner & your description of how clean the oil pan was I don't believe that it would be sludge blocking this passage, but in rare cases oil filter media has been known to tear, & sometimes a small piece of it can circulate & get lodged somewhere.

    If they retained the closed breather system when they installed the crate motor, be sure and take the oil filler cap off before you put the air pressure to the p.r. valve & passage.
    Last edited by stephan; 10-27-2010 at 02:47 AM.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  6. #6

    Default

    Nope. No oil cooler. Just the stock GM oil filter adapter just like the one shown here .

    I'll set the compressor to 35psi like you recommended, and test the passage that goes beyond the relief valve (outward flow direction from the oil filter). Hopefully I'll find a blockage/restriction in that passage and clean it out rather than having to tear into the engine and replacing the cam bearings. It's getting too cold out to do that kind of extensive work in an unheated garage. lol

    I'll post the results here sometime tomorrow.

    P.S. I almost forgot to ask about the "closed breather system"
    I'm not sure what that is. It does have an air cleaner that is not enclosed. It is open all the way around it's circumference. The valve covers are not stock either. The only opening on the left (driver's) side valve cover is for the PVC valve (that is where I have to fill the oil). The only opening on the right (passenger) side is for the breather tube that went to the stock air cleaner housing which was left open for several months without a filter/breather element attached to it (my own stupidity on the breather tube being left open). That breather tube has had a filter/breather element attached to it for I think at least one month before this high oil pressure problem started.
    Last edited by 86_C10; 10-27-2010 at 04:23 AM.

  7. #7
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    OK, on the o.f. adapter, go ahead and take it off. It'll give you easier access to blow out the passages. It will also give you a second chance to look & see if there's anything unusual in there again. That area never gets drained completely & is a good spot to look for residuals of "anything" that you might have not seen the first time. Also inspect the adapter carefully.
    When you replaced the oil pump did you change the oil & filter? If not I would take a shot at this before proceeding with anything else. I have never had a problem with an oil filter but I have never had a problem with too much oil press either & it is easier that the other things. Just to humor me, replace the oil filter with a different brand like an A.C. or a Fram.
    On the breather system: You had mentioned that there was extra oil around the valve covers, & I wanted to know what you had for a functioning b. system. Oil leaks at v.c. indicate high crankcase pressure. I have seen high c.c.press start to slow an engine & cause it to be sluggish, & that is the only thing I could think of that could even remotely be associated with that part of your problem. Pull the breather tube out & have a look & make sure it's clear. Pull the pcv valve out and shake it back & forth (it should rattle) If it doesn't it is either stuck open or closed. Can you remember anything that happened shortly before either of these problems started?
    The sluggish engine description & the high oil pressure don't go together. The only way I can think of to link them together would be if the oil pressure was so high that the oil pump was being worked excessively hard & if it was working hard enough to slow the engine down, it would have snapped the o.p. shaft off.

    edit** Cut your old oil filter open & see if there is anything unusual going on it it. Look for torn paper element, & residuals of anything

    edit** where did you check the oil press? At the top rear of block, or the one on lower left by the oil filter?
    Did you check it with engine warm or cold?
    Last edited by stephan; 10-27-2010 at 02:05 PM.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  8. #8

    Default

    I visually rechecked the oil filter adapter, and the cavity & passages for dirt, debris, etc.. Everything looked clean with the exception of some oil which is natural.

    I just ran the compressed air test on the p.r. valve side (outflow direction from oil filter) of the oil filter adapter cavity, at 30-35psi.
    Attachment 21977 Attachment 21978

    I've never done this before so I'm not sure what the resistance should feel like. I can feel that there is not a total blockage, however, I did feel a little resistance. Is this normal, or should the air have just flowed through completely resistance free?

    When the oil pump was replaced, even though the oil that came out was new, I replaced it anyway. The filter was also new, but not replaced after the new oil pump was installed. Let me explain in more detail which will also answer some of your questions in the last reply.

    Back around June or July of this year, there was a real bad storm heading toward the village I live in. I'm a storm spotter for the county I live in and for the National Weather Service Quad Cities IA/IL. I was parked out on the edge of town with the engine running when a report came in that a very strong straight line wind was about to hit where I was at. At the same time I noticed a funnel cloud forming right across the street from my location which was headed for the village and was going to pass directly over my house! I immediately hauled my butt home to get the family in the basement. Heavy acceleration and breaking occurred during a one minute time period to get home. The truck has an automatic transmission so the engine was not red lined or over revved. My speed did not go over 60 mph in that short distance. No spinning of the tires either. I pulled the truck straight into the garage, shut it down, and did not notice anything abnormal at that time. Prior to this event, the truck has always ran top notch with no indications of any problems.

    Either the next day, or the day after that, I started the truck to go somewhere. The oil pressure was in it's normal range of 30-45psi on the stock electrical oil gauge. The engine started and sounded normal also. After about maybe five miles down the road, I noticed a little hesitation going up a very slight incline. At this time the eng. temp. was normal, no check eng. light, but the oil pressure was a little above normal. It was about 50psi. I was about half-way to where I was going and just hoped to make it there. I could not pull over anywhere at that time to check things out. More than normal acceleration caused hestitation at all speeds up to 65mph. Don't know what it would do above 65mph.
    When I was able to stop and look things over, I discovered that the oil level was about 1 qt. low so I topped it off. When I started the engine, it ran perfectly fine but still had random high oil pressure around 50psi. Upon returning home, I decided to do an unexpected mid-summer oil & filter change to see if that would correct the high pressure problem. Pennzoil 10w30 and a Fram oil filter. 4qt.'s plus 1qt. for the filter. This did not make any difference to oil pressure other than noticing that the pressure was now sometimes hitting 50-57psi. Only using the truck at this point when absolutely necessary, over the next few days the oil pressure was staying at these higher psi's for longer periods of time and occasional hitting 60-60+psi. At this point I decided it was best to not drive it anymore.
    I replaced the oil sending unit which made no difference in readings. Now it was time to break out the mechanical test gauges. High pressure was verified by the mechanical gauges. At that time I figured one of the two pressure relief valves where sticking and decided to replace the oil pump which was the most likely out of the two. I installed the same type of pump that was originally in the engine, a Melling M55 standard pressure/standard volume oil pump. I refilled the oil pan with 4qt.'s Valvoline 10w30 but did not replace the oil filter since it had just been changed after the start of the high pressure problem. During the priming stage of the pump using a 0-1500 rpm electric drill, the gauge quickly hit 50psi and higher at about 3/4th trigger (approx. 1125 rpms) within about 6-7 seconds. I continued to fully prime the pump for about 30 seconds turning the primer tool just fast enough to keep the pressure around 40-45psi.
    After priming the pump and reinstalling the distributor, I started the engine and the mechanical gauge that goes from 0-50psi instantly went right past the 50psi and hit the back side of the zero pegging the needle to max. I shut down the engine immediately.
    Now I assumed the high pressure was being caused by the p.r. valve in the oil filter adapter. I removed the oil filter, visually inspected the oil filter adapter, then removed the adapter and visually inspected it, and the cavity in the block where it was removed from as well. No visible debris anywhere, the p.r. valve opened and closed freely by hand with little pressure.

    While I had the distributor out, I removed and inspected the cap & rotor. The cap was not in bad shape but I replaced it anyway. The rotor button was at the point of being questionable and I replaced it too. Now as far as the one occurrence of the engine being sluggish, I'm pretty sure I located the cause of that. I think it was due to the rotor button. There was quite a bit of loose carbon all around the center button in which I believe a small amount of that carbon dust became temporarily lodged between the tab on the rotor button and the button on the dist. cap. This sluggish incident only happened once as in the way I described above and never happened after that one time.

    "I have never had a problem with an oil filter but I have never had a problem with too much oil press either & it is easier that the other things. Just to humor me, replace the oil filter with a different brand like an A.C. or a Fram."

    I picked up two ACDelco oil filters today. In the past I've always used Fram. Just to rule out the possibility of two defective Fram oil filters in a row, I am going to install one these ACDelco oil filters. But, and this is a big 'but', I have a question for you stephan, since I removed the oil filter adapter without any damage to the gasket which is still attached to the block (no rips, tears, frays, etc.) is it safe to temporarily reinstall the oil filter adapter on this gasket for a quick oil pressure test with the ACDelco filter?

    About the valve cover gaskets: They are leaking a minimal amount of oil. They have not been changed in the 4-years (10,000 miles) that I've owned it. Last fall I noticed just a little bit of oil around a couple of corners. But now there is oil (even though very little) all around both v. covers. Maybe it is because of high pressure, maybe it is just time to replace them.
    The breather tube was removed this spring and replaced it with a little filter thingy as shown in the picture below..
    Attachment 21979
    As you may be able see, the engine is dusty, but the breather filter is absolutely clean. I can very easily blow through it.

    The PVC valve was replaced either last fall or this spring. It too is very clean other than the typical oil found inside it, the valve rattles freely and I can blow through it very easily too, as well as the hose coming from it going to the carb.

    The oil pressure tests are being performed through the fitting at the top rear of the engine. Should I also test at the other location you mentioned at the left of the oil filter housing? And is the bolt/plug in the picture below to the left of the oil filter housing and just above the oil pan the place that you are explaining?
    Attachment 21980

    I haven't cut open the oil filter yet, that will be done tomorrow. As far as the oil filter that was on the truck when this problem began, it was thrown away.

    Warm or clod testing: With the pressure being 60+psi, I do not let the engine run any longer than a few seconds. Test are being performed on a cold start.

  9. #9
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    Are you related to Count Leo Tolstoy? ha ha
    ok, no need to replace the filter again. I didn't know that it got a new filter after the first incident of high pressure, and no need to check the oil press. at the lower port either.
    Yes the resistance you felt was normal. 35 psi is mimicking a good oil press @ normal driving/rpms, so the problem is not there, as long as all the air didn't blow back at you, then it is ok.
    I don't think your hard driving had anything to do with either of these issues. (sluggish, or high oil press). If your short stint of hard driving brought it to the surface, then it was going to happen anyway.
    I have driven many small block Chevys harder than that for extended periods of time (hours) with no problems.
    The valve cover gaskets I thought might be related as much to the crank case breather & to the sluggish problem because too much crankcase pressure will find gasket weak spots & blow the oil out, but if the breather is clear then no worries there & is also not cause of the sluggishness. The oil from the vc gskts is more a problem of the high oil pressure only. Right now with such high press @ idle, you probably have as much oil up in the top end (3 quarts) as you would at 5,000 rpm if the press was normal & it just can't drain back fast enough.
    I don't know why the oil picked that particular time to be 1 qt. low. I don't think it is related to these issues, & was probably just a coincidence. May indicate that it is starting to burn some oil since it has 50k on it.
    You did everything right on priming the pump etc. Many people don't do important things like that lol. Also glad to hear you didn't go for the hp/hv Corvette pump.
    I tried all your links #77,78,79,80.& I got the v-bulletin message from the site: "invalid attachment specified" what ever that means... No worries about trying to resend them. I can tell that you know what you're doing & when you say the breather is clean, or the engine is clean that "it's clean" & you know what you're talkin about.
    I would go ahead & cut open the old filter. It will be well worth a look to see if you can see any metal between the pleats. Don't use a hack saw as it will contaminate it with metal fileings & you won't be able to tell what was in it before. Use tin snips if you have them. Use a Bowie knife or a big wood chisel to get a cut started for the tin snips. Cut it near the top ring so you don't have to cut it twice. Spread a nice big sheet of clean newspaper out to dissect the filter paper onto. Don't do any cutting of the metal filter cannister over the paper or small metal pieces can get on the paper & you might think they came out of the filter.
    I have re-read & see that on the day when you noticed it was sluggish & oil press was high the engine was running at normal operating temp. This answers a que & changes my mind about the cold temps & cold oil being partially responsible.
    Yes reusing the adapter gasket is fine. It probably won't ever leak. Just keep an eye on it for a few days. Usually if they are going to leak because they were disturbed, they will leak right away.
    Oil press. check up top or on the side. I only wanted to know where you checked it because I thought you might have checked it on the lower left by the o.f. & it would have read higher there. Top rear where you checked it is the best place because it will show you the minimum there & most cases low oil press is the prob people are trying to check.
    You have done everything correctly since this began, (oil pump, oil change, o filter, o.f. adapter, bypass valve,etc) to eliminate the things I would have tried first, & unfortunately the high o.p. is still pointing to a bearing that has moved or spun and is covering one or more oil passages. I just can't imagine that happening in a GM crate engine because they are usually bullet proof. If you find metal in the oil filter that will confirm it & we will go from there. If you find no metal in the filter, then before you start tearing it down, give me a few more days & I will call some old timers that might have 1 or 2 more things to check first.

    edit** Forgot to tell you to use scissors to cut the filter paper. They work a lot better than a knife. Be sure & wipe off the oil before returning them to your wife ha ha
    Last edited by stephan; 10-28-2010 at 02:21 AM.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  10. #10

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    lol. Sorry about that. My last post almost was a small novel, but there was quite a bit to explain.

    You have a great personality stephan! I like that. You seem like a really nice, and well educated person. A rare bread these days!
    I see the problem that you mentioned about not being able to view the images I posted. They are there, you just can't see them using Windows Internet Explorer. The problem is due to the program coding of this forum. I am also a webmaster (design & maintenance of websites). If you use Mozilla Firefox, a much more secure, faster and reliable web browser, then you can see them.

    "Right now with such high press @ idle, you probably have as much oil up in the top end (3 quarts) as you would at 5,000 rpm if the press was normal & it just can't drain back fast enough."

    I'm starting to wonder now if that 1-2 year period where the breather tube was open (unfiltered), if a moth, spider or bug of some sort got into it somehow and just recently became lodged in a passage. I live smack dab in the middle of farm country, lots of bugs out here, and dust too! lol. Over the next couple of days I'm going to remove both v. covers and see what it looks like in there. Is it at all possible that there could be a restriction or blockage in the right bank that would result in this weird gradual increase in oil pressure?

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