low oil-pressure

[FishinRanger]

My '91 Ranger oil gauge has always been steady on the 'N' of NORMAL, until I got an oil change at the dealer. Now it's bouncing around, but generally goes down to red line and stays there.
I've read many places that this is a 'dummy' gauge and there's "usually" something wrong with the sending unit. BUT, why would it suddenly go bad after an oil change???
That was the first change since I bought the truck...so who knows what oil weight was in there before.
So, today I changed the oil to 20w-50 and added a bottle of STP just to see if the dealer put in 5w-30 and it was too thin for a truck w/90K miles.
Same low/bouncing reading on gauge still. Also, before, when I took the oil cap off with the engine running to add some Gunk oil-detergent, the engine started to bog down.
Is my engine toast??

Thanks--
(I know I'll have to go to dealer to get pressure checked with real gauge, but just wanted off-hand opinions/experiences)

 

[289-tiger-]

My '91 Ranger oil gauge has always been steady on the 'N' of NORMAL, until I got an oil change at the dealer. Now it's bouncing around, but generally goes down to red line and stays there.
I've read many places that this is a 'dummy' gauge and there's "usually" something wrong with the sending unit. BUT, why would it suddenly go bad after an oil change???
That was the first change since I bought the truck...so who knows what oil weight was in there before.
So, today I changed the oil to 20w-50 and added a bottle of STP just to see if the dealer put in 5w-30 and it was too thin for a truck w/90K miles.
Same low/bouncing reading on gauge still. Also, before, when I took the oil cap off with the engine running to add some Gunk oil-detergent, the engine started to bog down.
Is my engine toast??

Thanks--
(I know I'll have to go to dealer to get pressure checked with real gauge, but just wanted off-hand opinions/experiences)

No offense intended but get that 20W-50 out of there, save that stuff for air cooled VW's. 5 or 10W30 in before the valve train is damaged.

 

[Giant squid]

ALSO Putting detergent can be a terrible thing to an older engine. You free'd up all the gunk and now its roaming around your engine ruining bearings and plugging other small passages. Just be aware.

 

[289-tiger-]

ALSO Putting detergent can be a terrible thing to an older engine. You free'd up all the gunk and now its roaming around your engine ruining bearings and plugging other small passages. Just be aware.

Correct Squid, at least though in the thick oil it will only go as far as the oil does.

Good evening

 

[FishinRanger]

20w-50 is getting drained tomorrow & 10w-30 put in. I haven't driven it yet...just let it run in the garage for 10-15 min. I just wanted to see if the thinner oil was leaking through somewhere (maybe the PO had some thicker "motor honey" stuff keeping the pressure stable?).
As for the low pressure _immediately_ following the dealer's oil change...what do you guys think?

 

[Wicked_Sludge]

things work up to a point then they fail...thats just how vehicles are. its pretty hard to screw up an oil change (it can be done though).

 

[289-tiger-]

20w-50 is getting drained tomorrow & 10w-30 put in. I haven't driven it yet...just let it run in the garage for 10-15 min. I just wanted to see if the thinner oil was leaking through somewhere (maybe the PO had some thicker "motor honey" stuff keeping the pressure stable?).
As for the low pressure _immediately_ following the dealer's oil change...what do you guys think?

Good, 90k is pretty low for a 91, hope you get many more miles from it. The sending unit may have material blocking its passage or entering its diapragm that could happen after an oil change. To put you at ease if you do not have a mechanical gauge, listen for the filter (new) and system priming immediately after start up after the oil change. (No clicking or knocking after a few seconds is good)

Good luck

 

[Big Jim M]

Oil filters have a bypass valve in them...Did you change the filter also? If not change to a good brand and see if that is your problem.
Big Jim

 

[FishinRanger]

The dealer put in a Purolator filter and I just put in a high-end AC-Delco (black).
It's going in tomorrow for pressure test.

 

[Wicked_Sludge]

your ford dealer used a purolator filter?

or by "dealer" do you mean "not dealer".

 

[Sasquatch_Ryda]

Just replace the sending unit, it an under $10 dollar part, I betcha your problem goes away. That gauge really has nothing to do with actual oil pressure. Another thing to check is to see if the wire that goes to the terminal of the sending unit is loose fitting on it or if its full of corrosion. Clean it up and put some die electric grease in it.

 

[FishinRanger]

Bad sending unit. I have plenty of pressure.

Thanks guys....close the book on this thread.

Now, on to the transfer-case motor and cab-corner supports.

edit: yup, Purolator...I think they have different levels of oil change. If you want Motorcraft and non-bulk oil it costs more.

 

[Sasquatch_Ryda]

Wow, we don't have anything but Motorcraft oil filters at the dealership i work at.

 

[Wicked_Sludge]

ya, the dealership here is the same way. on the rare occasion we get a non-ford product in, it gets a carquest (wix) filter. all fords get motorcraft.

 

[Evan]

I thought the position of the RBV oil pressure gauges is pretty much meaningless.