I have a 1997 F150 with the 4.2 Liter V-6. Here’s my problem. After I run the engine about 20 minutes, the oil pressure gauge starts to fluctuate at idle. It’s fine when the RPMs are up.

I have changed the oil sending unit, put in new plugs and wires, and changed the oil (I suspected that I may be getting viscosity breakdown due to water in the oil). The oil is not showing any signs of having water / coolant in it.

Not sure what to try next. My thoughts are to check the oil pressure at the sending unit to make sure I am not getting a false reading. If it is losing pressure I was going to change out the oil pump and see if that helped. Trying to get the easy things out of the way first.

The engine only has 90K miles. Any help would be appreciated.

Parrothead

 

I got the same problem, i was told that my gauge might be wrong, or like you said mabye the signs of a oil pump goin bad. All i know is that i dont know what the deal is, and i wanna find out cause i gotta few more miles on mine(115,000) than you do??IT's strange though cause when you raise the RPM"s then it stops flucuating. I aint got the money right to buy a new oil pump, but if you find out the problem man, please let me know, id really appreciate it! Oh yeah is urs a 5 speed manual tranny??

97 4.2 5speed
SIngle cab flareside

 

Install a mechanical oil pressure gauge. Check the readings at cold start,warmed up,and cruising speed. I think oil pressure should be 40-60 psi at idle. Theoretically,an engine can survive on 10 psi for every 1000 rpm.Thats too low for me tho. :santa:

 

Well, a solution has been found.

The intake gasket leaked coolant into the oil. Main bearings are shot. Needs a complete overhaul.

Opted to replace the engine.

If your oil gauge is fluctuating, test for coolant in the oil. Catch it early so you don't have to replace engines.

P.S. - This 97 F150 is my last Ford product. Nothing but problems for 7 years.

 

well mine decided it wanted to do the oil pressure fluctuation the day after i put on te underdrive pulley and was rollin down the interstate at 65 mph pullin my 3000 lb. boat and trailer and when i came to a stop and idled for a second it started bouncin then just above idle it would go back to normal.

I changed the oil right after that happened and it didnt do it right away. then i drove it to work the next day and it was doing it when i got off the interstate. was looking into replacing the oil pump. and also checked the ford website to look into an 04 model. must have scared my truck into working right again. no fluctuation today at all. might seem that my gauge reads alittle lower then it used to (but still more towards the high side then the low side) now but i might be imagining that.

my theory is i either got some gunk in the releif valve from the intake gasket replacement even though i was very careful to do a clean job. and changed the oil before starting it and ran 2 quarts through it to get any gunk out. or the pump is going out from the load i put on it pulling the boat.

116k now and im gonna let it be for now and wait and see if it ever does it again.

and for those that are wondering it is a 5 speed manual. im starting to see a trend with the oil pressue fluctuations on the manuals. maybe the autos just idle alittle higher so it is not noticable.

I've had mine since 97 and i still love it even with its quirks. and the 04s body doesnt appeal to me much. i liked how they were rounded kinda reminded me of the 50s style alittle.

 

mine has the exact same problem.It started yesterday.I was wondering if you had your timing cover gasket changed recently.A friend of mine who is a mechanic said particals could of fallen in the holes they changed it.

 

i had the timing cover done along time ago. but i just recently did the lower intake gaskets. it is possably some gunk got in there or i dislogded some gunk when i did that but i was real careful. but at 116k im thinking oil pump and if that dont fix it replaceing the pressure releif valve in the front cover but i really dont want to pull front cover again. maybe if i order one of those high performance cams i will.

the oil pump is the easiest to change and what i will start with when i get money for a new pump. its only remove filter remove the six bolts replace o-ring and install new pump. should take about 5 minutes.

 

hmmm i just came up with another theory to why this might seem to affect the manual 5 speeds more. and why it only happens when its warmed up. I'm thinking the IAC motor might be sticking. I might have to try that first thats way easier to change then an oil pump.

bad IAC motors on autos ussually cause stalling when shifted from park to drive or reverse because of the load and the way the idle drops. on manuals they always run at about 850 rpm maybe my iac is runnin it at 750 rpm and i cant detect the differenct on my little tach.

i'm gonna have to look into this more tommarrow.

the guys over at the t-bird site are having the same issuse with some of the 3.8 L in manual super coupes they say they replace IAC and all is good.

 

Mine is auto and doesnt stall so it must not be that.

 

So i need to get a new IAC motor, I just just changed my oil and didnt find ne coolant, but im checkin it on a regualr basis now. Where can i go to find an IAC motor????


97' Ford Flareside
4.2 liter V6 5speed
Reg Cab

 

ok i checked my oil pressure and this is what i got:

cold start at idle 70-80 psi

idle 850 rpm HOT when gauge is bouncing 14-25 psi

HOT at 2500 rpm 40-45 psi this is the one they use to see if its in specs.

SPECs are 40-125 psi hot at 2500 rpm. so I'm gonna do some more research and figure out what this means before replacing anything.

i fear it is indicating worn bearings because of the big drop in pressure once its hot. i'll let you know if i get more info.

 

HAve you found ne more info about it mabye being the bearings?? Could mine be going out at 116,000 miles, and when is the reccommended time to change the spark plugs and wires??

 

it very well could be bearings and it is looking more like bearings now that i have changed the sender ran an oil pressure check and am still losing oil pressure hot.

 

Mr B,what weight oil are you using? If you want a temporary fix,try using a single weight oil,like 30 weight,to start.If that then makes the pressure still drop,go to a 50 weight.I use to rebuild SBC engines and before rebuilding some of them ide run Kendall Nitro 70 weight in them.It was a temporary fix until I rebuilt them.One more tip;use no name brand oils.They are cheaper in price and you can save over using name brand.Good luck and keep us posted. :santa:

 

i was pullin the boat along today and i noticed my temp gauge was climbing higher then it normally does. i think i might have just wore out this 4.2 at 116k prolly waited to long on the intake leak. looking at acouple different fords to replace as the tow vehicle but i will keep the 4.2 and put in a new motor when the time comes. it hasnt started knocking yet.