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HELP!!!! Oil pressure/Temperature Problem...........

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Can Can, May 12, 2001.

  1. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Today when I fired up the 84, I noticed that the oil pressure gauge was reading a tad low(3 or 4 PSI lower than normal). I've learned to ignore little things like that in the last few years- most of the time they disappear within a day anyhow!!!!!![​IMG] Anyway, we started out on the highway and it wasn't long before I noticed that my temp gauge was reading a wee bit higher, like 10-15 degrees higher than normal. It stayed like that for the entire trip(about 70 miles).

    At the first light I hit when I got into the city, the oil pressure gauge dropped to about 14PSI(the truck normally runs at around 30 hot)and the temp climbed another 15 degrees. I threw the tranny into neutral, pumped up the RPMs, and she started to cool down a bit, but the oil pressure stayed low.

    I pulled over and checked as much as I could- Oil was clean and full, coolant was full and circulating, and thermostat was open. SO......................<font color=red>WTF??????????????</font color=red>For what it's worth, I put on about 200 miles today and there were no other problems other than the fluctuating temps and pressures.

    Do oil pumps break down slowly, or do they just stop working? I'm worried that my oil pump is about to let go........

    Any suggestions would be much appreciated!!!!!!!!!!!!


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  2. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    I would pull a valve cover a make sure it still can make a mess.
    Sounds like a plugged system or pickup problem.
    Is the oil foamy? (leak in pickup tube)
    Does the oil smell bad?
     
  3. Jeff427

    Jeff427 1/2 ton status

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    Hey Canmore, my dad has a 76 3/4 ton Chevy with 200,000+ miles on it that hasn't been opened. It reads 0 psi [​IMG] on the gauge at an idle, it reads about 10 going down the road. It has been this way for about 5 years, and we use it to plow snow [​IMG]. The only way I know of that the oil pump can completely fail is if you twist off the oil pump drive shaft. They usually just get weaker over time. If it worries you, I'm fairly sure that you can change the oil pump with the motor still in your Blazer, just drain the oil drop the pan and change the pump. The temp problem may be related to your thermostat, or the internal condition of your radiator. You may need to flush the radiator, and/or change the thermostat.

    BTW, did you get the CHEVROLET sticker installed OK [​IMG]? I'm really looking forward to getting the twilight picture of your Blazer [​IMG]. Let me know.

    Jeff427
    <font color=red>Mud Dog Off Road Club</font color=red>
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  4. Twiz

    Twiz 1/2 ton status

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    Oil pressure has more to do with bearing clearance (crankshaft/rod bearings) than the oil pump. Oil pumps on s.m.c. rearly get worn to an extent that it would lower the oil pressure gage reading.(-in my opinion-) It might help if you think of it like this; Take a garden hose and pinch the end (reduce the clearance) the water pressure in the hose goes up. Open up the end (increase the clearance) and water pressure in the hose gose down.-does that make sense? So if the bearing clearance has worn- the oil pressure would go down.

    Stock oil pressure gages are known to be off- they are just a little better than a "dummy light". A.M. gages are a tad more acurate (depending on the quality of the gage). Also, oil pressure sending units can get gummed up and cause a sudden change in oil preasure gage readings. Heat will also reduce oil pressure by thining out the oil. Oil viscosity also has a impact on oil pressure. What oil do you have in it now? 5/30 is to thin for the summer, I think. 10/30 is perfect, You might want to go one step higher and see if it changes your gage reading. Some of the newer engines run 4 - 8 lbs of oil pressure at idle- right out of the factory.

    Random thoughts- hope it helps out.

    Twiztid
     
  5. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    What I am worried about here is the perceived changes thay
    Can experienced. If those cahnges are real, something (bad)is going on....
    Any updates
     
  6. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Twiztid- I'm currently running 10w30. Always have and always will. I realize that heat thins out the oil, but how much could a 10-15 degree increase in operating temperature affect my pressure?

    Thanks for the concern, 96C4. I think I've got the problem figured out-

    This morning, I took the truck out for a little test run. Today the oil pressure was normal at start up(FRIGGIN TRUCK!!!)[​IMG] Once I got going, I kept a close eye on my gauges. I waited for the temps to rise and watched the temp gauge drop when the thermostat opened. So far so good............ While driving up one of our bigger hills here in town, the temp started to rise again but the oil pressure never moved. I turned around and went downhill and she cooled off again. I took her out on the highway for a couple of miles and only then did I get any movement from the oil pressure gauge- My pressure dropped about 5 pounds and my temp increased about 10 degrees.

    I think my thermostat is the culprit. I'd been driving for at least 10 minutes before I saw my PSI budge, and that was only once I'd been on the highway for a few minutes. There was a lot of movement on the temp gauge though.

    I'll replace the thermostat tomorrow after work and let you know if that helps out. My only question is- How much does a 10-15 degree increase affect oil viscosity? Does it seem right that yesterday my oil pressure dropped so much with only a slight increase in operating temperature?

    Jeff- I haven't installed the sticker yet[​IMG]........Things have been a little hectic over the last few weeks. I'll let you know the minute it's on and I'll make sure to get some good pics showing the reflective capability!!!!



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  7. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    10 - 15 degree WATER may translate into 50 + degree in oil temp. The Vette oil temp is so high it is scary - but normal.
    And the pressure does not fluctuate once it is at operating temp.
    Replace your oil sending unit when you do the thermostat. Is it electric or mechanical?
    This is a good one!
     
  8. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    The oil sending unit is electrical, 96C4. Might be worth changing out while I'm under the hood.

    My wife had the truck out for about a half an hour this afternoon- according to her, oil pressure was slightly lower than normal and temp was slightly higher once again. This was at city speeds....

    Doesn't it make sense that if the truck is running a little too warm, the oil will be a little thinner and as a result offer less resistance = lowered oil pressure??????

    My main worry is that my oil pump is ready to die, but everyone I've talked to and everything I've read tells me that when an oil pump goes, it goes NOW!!! If thats the case, then the oil pump probably isn't the problem.

    The next logical cause would have to be a faulty thermostat. If a small increase in op. temp can cause the oil to get much hotter and thinner, this would explain why both problems are occuring at the same time...............

    Once again, I'll keep you posted.




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  9. Jeff427

    Jeff427 1/2 ton status

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    Canmore,
    I personally know of three different instances where oil pumps failed, and it was always the oil pump driveshaft twisting off, either because something jammed the pump gears, or because someone was using 20w50 with a high volume pump, on a -30 degree day, without warming up his truck (my uncle). There was nothing progressive about it either, it was normal pressure, then suddenly none. I don't think you have to worry about the pump failing.

    Jeff427
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