Why all of a sudden is my oil pressure dropping? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

JoetheMobster · 03-23-2002, 06:57 PM

Hey folks,

Just changed the oil in my truck for the first time (haven't had it THAT long, so I hope it was changed at least once, before I got it...hahaha) Anyway, after changing the oil and filter, I fired 'er up, and looked for leaks around oil filter, and drain plug. Seems to be none. So I decide to take the ol' pig out for a boot, and I notice that my oil pressure gauge is reading just above the "half" mark as I'm pulling out of the driveway. As I'm heading to drop off the old oil, I notice the pressure gauge is dropping slowly! When I get back to the house, the gauge is just below the "quarter" mark!! What the heck is going on here? The dipstick says that it's topped up, and there seems to be no leaks. Anyone have any suggestions? I'd hate to seize the motor, as I don't have the space, or the money to do a rebuild, or replacement.

------------------
1970 GMC 1500, 350ci, 3 in a tree

http://members.tripod.com/~Jungleman_2/1970GMC.html

Vancouver, B.C.

JoetheMobster · 03-23-2002, 07:01 PM

Sorry for the double post! (almost same message below this one) I finished typing it, and Internet Explorer crashed as I hit the "post" button, so I didn't think it made it! I tried to delete it, but very bad things happened! hahaa

------------------
1970 GMC 1500, 350ci, 3 in a tree

http://members.tripod.com/~Jungleman_2/1970GMC.html

Vancouver, B.C.

slam33 · 03-23-2002, 07:32 PM

what was in it before you changed it. 30wt, 40wt, 10w40 ?. you might have got a thinner oil.

------------------
71 basic C-10 350. The only option is the rust.No nothing on it, but thats all about to change. <A HREF="http://www.geocities.com/stevemau/slam33page.html?1004806705410

" TARGET=_blank>http://www.geocities.com/stevemau/slam33page.html?1004806705410

</A>

71GMCstreet · 03-23-2002, 07:35 PM

Thinner oil, lower pressure.

67Blacksheep · 03-23-2002, 09:54 PM

Mobster-
Like the others suggest, it is probably that you put the correct oil in, and someone before you had heavier in it. Does the engine have any noise now with the thinner oil?? Shame to say, but alot of folks load engines up with thick additives before they sell.( ie- Motor Honey ). If you are worried about seizing your engine, put a mechanical guage on it and get as accurate as possible. Truth be told, it doesn't take THAT many pounds to keep the engine lubed, just ensure you have enough!

------------------

mooneyes · 03-23-2002, 10:48 PM

rule of thumb 10lbs at idle and 10lbs for every 1,000 rpm's after

------------------
70 short step from vegas woo hoo !!!Ken Lyons Slippery Rock PA yahoo messenger:mooneyes4b "things always look different from higher up" Clint Eastwood (fist full of dollars)

JoetheMobster · 03-24-2002, 02:26 AM

Sorry for such a long delay in responding, I was outta the house all day. I have no idea what was in the truck before changing the oil, as it was the same crap that was in there when I bought it. It was black, stinkin like a dirty arsehole and was pretty thick! I don't think it's been changed in a l-o-n-g time! Guy that had it before me, used to like to drive it hard! He was showing me the truck before I bought it, and was revving the engine up to about 6 grand! (not in gear) I was imagining that that's not very healthy to do very often! Usually I shift at about 2500-3000 rpm. I put in fresh 30w (10w30) oil, 5 liters of it. I had to fight the damn oil filter off! The guy that owned it before me must have used damn impact wrench to tighten the oil filter on! I bought an "oil filter socket" that was made out of "super graphite, made in the USA" and I shattered it in the first try! I got a replacment, and that ended up rounding off the oil filter's notches! I finally bought an adjustable clamping wrench, again (damn tools, once lent out, they never seem to come back, haha) and that finally did the trick. BTW, I didn't re-tighten the new oil filter to 180 ft/lbs! lol! The oil level seems to be alright, I'll re-check it in the morn' and see if anything has changed.

------------------
1970 GMC 1500, 350ci, 3 in a tree

http://members.tripod.com/~Jungleman_2/1970GMC.html

Vancouver, B.C.

[This message has been edited by JoetheMobster (edited March 24, 2002).]

kurts72 · 03-24-2002, 08:27 AM

Joe, when the oil warms up the oil pressure will drop quite a bit. I have owned vehicles that the oil pressure "gauge" has said nearly zero and I never had any problems. As long as you don't hear engine knocking at idle you are ok. I like to run thick oil 20w50 summer and 10w40 winter and never had any problems. Good luck

Longhorn Man · 03-24-2002, 10:15 AM

I agree with kurt on oil thickness. When you don't know how many miles are on an engine, it is nice to have thicker oil taking up the possable extra clearance on the main and rod bearings.

------------------
'69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man
I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it.
Need to pick up the one ton Longhorn with a PONTIAC 350/350soon.
Thanks every one!

Check out The Longhorn Webite.
If you need a pic posted, E-mail me at longhornmail@yahoo.com
Andy, in Columbus Ohio

lukecp · 03-24-2002, 10:54 AM

Before i got my engine rebuilt, i switched from 10w30 to 20w50 oil. The heavier stuff made the oil pressure rise a little bit, and it didn't smoke quite as much. You could drain out the oil that is in it now and put in some heavier stuff, but that would be a waste of $10 or so....

------------------
Lucas

drop_shift@hotmail.com

My Daily-Driver: '72 Chevy LWB Custom/10. Rebuilt 350, 300 HP thanks to a few go-fast goodies. Ochre with a white top. Future plans include a frame off restoration, and maybe a blown 383.

*nucleus* · 03-24-2002, 11:43 AM

10w will go through an old engine like real Mexican food through a gringo. 20w is better - I run 30w until I can afford a rebuilt long block (it stills smokes, but consumption is down)

I prefer 'straight' weights rather than blends. If your cooling system is working ok then your engine running temp should be consistent. Starting temp makes some difference with heavier oils (unless garaged or not in a cold climate)

------------------
: 69 C20
: anything with tits or wheels is nothing but trouble ...

03-23-2002, 06:57 PM	#1
JoetheMobster Listening since '86 Join Date: Sep 2001 Location: Canada Posts: 1,799	Why all of a sudden is my oil pressure dropping? Hey folks, Just changed the oil in my truck for the first time (haven't had it THAT long, so I hope it was changed at least once, before I got it...hahaha) Anyway, after changing the oil and filter, I fired 'er up, and looked for leaks around oil filter, and drain plug. Seems to be none. So I decide to take the ol' pig out for a boot, and I notice that my oil pressure gauge is reading just above the "half" mark as I'm pulling out of the driveway. As I'm heading to drop off the old oil, I notice the pressure gauge is dropping slowly! When I get back to the house, the gauge is just below the "quarter" mark!! What the heck is going on here? The dipstick says that it's topped up, and there seems to be no leaks. Anyone have any suggestions? I'd hate to seize the motor, as I don't have the space, or the money to do a rebuild, or replacement. ------------------ 1970 GMC 1500, 350ci, 3 in a tree http://members.tripod.com/~Jungleman_2/1970GMC.html Vancouver, B.C. __________________ 2007 Saturn Aura - hey it WAS a GM product

03-23-2002, 07:01 PM	#2
JoetheMobster Listening since '86 Join Date: Sep 2001 Location: Canada Posts: 1,799	Sorry for the double post! (almost same message below this one) I finished typing it, and Internet Explorer crashed as I hit the "post" button, so I didn't think it made it! I tried to delete it, but very bad things happened! hahaa ------------------ 1970 GMC 1500, 350ci, 3 in a tree http://members.tripod.com/~Jungleman_2/1970GMC.html Vancouver, B.C. __________________ 2007 Saturn Aura - hey it WAS a GM product

03-23-2002, 07:32 PM	#3
slam33 Registered User Join Date: Aug 2001 Location: Long Beach, Ca Posts: 1,432	what was in it before you changed it. 30wt, 40wt, 10w40 ?. you might have got a thinner oil. ------------------ 71 basic C-10 350. The only option is the rust.No nothing on it, but thats all about to change. <A HREF="http://www.geocities.com/stevemau/slam33page.html?1004806705410 " TARGET=_blank>http://www.geocities.com/stevemau/slam33page.html?1004806705410 </A> __________________ 71 LWB 350/350still working on it but it's going tp be sweet. www.geocities.com/stevemau/slam33page.html " TARGET=_blank>http://www.geocities.com/stevemau/slam33page.html?1004806705410 </A>

03-23-2002, 09:54 PM	#5
67Blacksheep Registered User Join Date: Mar 2002 Location: Ohio Posts: 135	Mobster- Like the others suggest, it is probably that you put the correct oil in, and someone before you had heavier in it. Does the engine have any noise now with the thinner oil?? Shame to say, but alot of folks load engines up with thick additives before they sell.( ie- Motor Honey ). If you are worried about seizing your engine, put a mechanical guage on it and get as accurate as possible. Truth be told, it doesn't take THAT many pounds to keep the engine lubed, just ensure you have enough! ------------------ __________________ '94 GMC Seirra Ext. Cab '67 Formula Firebird '89 GSX-R 750

03-23-2002, 10:48 PM	#6
mooneyes Registered User Join Date: Jan 2002 Location: Slippery Rock PA USA Posts: 1,692	rule of thumb 10lbs at idle and 10lbs for every 1,000 rpm's after ------------------ 70 short step from vegas woo hoo !!!Ken Lyons Slippery Rock PA yahoo messenger:mooneyes4b "things always look different from higher up" Clint Eastwood (fist full of dollars) __________________ Ken Lyons, Slippery rock pa 68 short step 327 t10 4 gear 72 2wd blazer project 70 lwb 305/700r driver 78 caprice project 02 cavalier D.D ( hate it!!)

03-23-2002, 07:35 PM	#4
71GMCstreet Registered User Join Date: Dec 2001 Posts: 97	Thinner oil, lower pressure.

03-24-2002, 02:26 AM	#7
JoetheMobster Listening since '86 Join Date: Sep 2001 Location: Canada Posts: 1,799	Sorry for such a long delay in responding, I was outta the house all day. I have no idea what was in the truck before changing the oil, as it was the same crap that was in there when I bought it. It was black, stinkin like a dirty arsehole and was pretty thick! I don't think it's been changed in a l-o-n-g time! Guy that had it before me, used to like to drive it hard! He was showing me the truck before I bought it, and was revving the engine up to about 6 grand! (not in gear) I was imagining that that's not very healthy to do very often! Usually I shift at about 2500-3000 rpm. I put in fresh 30w (10w30) oil, 5 liters of it. I had to fight the damn oil filter off! The guy that owned it before me must have used damn impact wrench to tighten the oil filter on! I bought an "oil filter socket" that was made out of "super graphite, made in the USA" and I shattered it in the first try! I got a replacment, and that ended up rounding off the oil filter's notches! I finally bought an adjustable clamping wrench, again (damn tools, once lent out, they never seem to come back, haha) and that finally did the trick. BTW, I didn't re-tighten the new oil filter to 180 ft/lbs! lol! The oil level seems to be alright, I'll re-check it in the morn' and see if anything has changed. ------------------ 1970 GMC 1500, 350ci, 3 in a tree http://members.tripod.com/~Jungleman_2/1970GMC.html Vancouver, B.C. [This message has been edited by JoetheMobster (edited March 24, 2002).] __________________ 2007 Saturn Aura - hey it WAS a GM product

03-24-2002, 08:27 AM	#8
kurts72 Registered User Join Date: Dec 2001 Location: Durand, IL Posts: 98	Joe, when the oil warms up the oil pressure will drop quite a bit. I have owned vehicles that the oil pressure "gauge" has said nearly zero and I never had any problems. As long as you don't hear engine knocking at idle you are ok. I like to run thick oil 20w50 summer and 10w40 winter and never had any problems. Good luck __________________ Kurt in Durand, IL

03-24-2002, 10:15 AM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	I agree with kurt on oil thickness. When you don't know how many miles are on an engine, it is nice to have thicker oil taking up the possable extra clearance on the main and rod bearings. ------------------ '69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it. Need to pick up the one ton Longhorn with a PONTIAC 350/350soon. Thanks every one! Check out The Longhorn Webite. If you need a pic posted, E-mail me at longhornmail@yahoo.com Andy, in Columbus Ohio

03-24-2002, 10:54 AM	#10
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	Before i got my engine rebuilt, i switched from 10w30 to 20w50 oil. The heavier stuff made the oil pressure rise a little bit, and it didn't smoke quite as much. You could drain out the oil that is in it now and put in some heavier stuff, but that would be a waste of $10 or so.... ------------------ Lucas drop_shift@hotmail.com My Daily-Driver: '72 Chevy LWB Custom/10. Rebuilt 350, 300 HP thanks to a few go-fast goodies. Ochre with a white top. Future plans include a frame off restoration, and maybe a blown 383. __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

03-24-2002, 11:43 AM	#11
nucleus Account Suspended Join Date: Dec 2001 Location: U$A Posts: 896	10w will go through an old engine like real Mexican food through a gringo. 20w is better - I run 30w until I can afford a rebuilt long block (it stills smokes, but consumption is down) I prefer 'straight' weights rather than blends. If your cooling system is working ok then your engine running temp should be consistent. Starting temp makes some difference with heavier oils (unless garaged or not in a cold climate) ------------------ : 69 C20 : anything with tits or wheels is nothing but trouble ...

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