1997 4.2L F-150 Oil Sending Unit

Ok, my oil pressure on my truck gets low and the needle starts bouncing when at low idle speeds (in drive or reverse) but returns to normal pressure when in park or neutral. This all happens after it warms up, and the oil pressure gauge will be all the way at zero at some times.

I replaced the oil pump, oil filter and oil (K&N oil filter, Royal Purple 5w-30, and a Melling oil pump). It still does it. So I ran some sea-foam through my fuel and my oil, and it helped out tremendously, although the needle is still bouncing a little bit and still making noises. I have had had all the lifters replaced as well.

I just bought a new oil sending unit to install. Now what I want to know is, if the location of the sending unit is high enough to where I can just change it without draining the oil, and if there is anything I should do specifically when changing it.

If this doesn't work I'm pulling the motor and changing the sending tube and the oil pan gasket and will scrub the stuff down real good, but hopefully it's just the sending unit is bad.

i hate to be the bear of bad news but.....when in reverse or drive your putting a load on the engine as where in nuetral or park your not. i'd say main bearing are wore out because it does it when warm.

Did you drain the oil after you put the seafoam in?

I just changed the oil to Royal Purple about 300 miles ago, and put in the sea-foam. I figured it can have a nice long oil life to clean the motor out. the motor just reached 135,000 miles so it is still very young for a 4.2L and when it was getting the lifters changed it still looked fairly new.

medwards29 said:

I just changed the oil to Royal Purple about 300 miles ago, and put in the sea-foam. I figured it can have a nice long oil life to clean the motor out. the motor just reached 135,000 miles so it is still very young for a 4.2L and when it was getting the lifters changed it still looked fairly new.

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Let me get this straight... you have been running the engine for the past 300 miles with the seafoam in the oil?!?!?! You need a set of bearings now for sure . You are suppose to put that in, run it for about 15-20 min and drain the oil.

And 130k is alot of miles for a 4.2. Most only make it to 100k before a catastrophic failure. those engines are garbage

ya man if the seafoam has been in there for 300 miles your bearings are toast!! get ready for another motor!

91idi said:

It doesn't have 300 miles on the sea foam. Thanks for the heads up on the sea foam, the bottle says you can use it for extened periods of time.

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Yeah. in the fuel system

an oil pump does not create oil pressure persay, all it does is pump oil, your rod bearings, main bearings, and cam bearings create oil pressure. reason i say that is if they are wore, your oil pressure will go down. also the first thing to do is ck oil pressure with a mechanical gauge, not to throw parts at it for the hope of fixing it. since you stated that your hearing noises and had the lifters changed i would say you have a oil pressure problem. but right now your best bet is to change your oil with straight 50w oil, and see what your oil pressure is then. when you change your oil with thicker oil, and your oil pressure is better, that pretty much says you have a bearing clearance problem, which i would almost bet money you do. but i have seen a oil pump screen half stopped up and have this same issue, and the 4.2 is a good engine, i know of plenty of them with superchargers and turbochargers and they unleash hell on them and they hold up. but sometimes a mass produced engine will not last as long as some others.

why don't I just install the new oil pressure sending unit I just bought for 10 bucks and see if that fixes it and possibly save me the time and money because I'm almost 100% positive that it is the problem seeing that the 4.2L f-150 is notorious for oil pressure sending unit failures. All I asked was if I had to drain the oil to install it but nevermind, I'll just install it on my next oil change. Thanks for your opinions.

Medwards29 - Did you replace the oil sending unit and did it solve the bouncing needle condition? I have the same problem with the same engine and plan to replace the sending unit this weekend. I've never replaced one before, but from asking around it seems to be faily simple. I've heard that the special socket isn't necessary, but we'll see. I'll let you know how mine goes.

Depends on the year of the engine. 97-98 had intake problems that would cause dumb stuff like hydrolocking and such.

99+ are good. I have seen many at 200,000 plus with little maintance. I have a 2000 model that runs great.

The sending unit is a very common problem with these trucks. It is located near the oil filter on these engines. The part is about 10 bucks. You will loose some oil. I would advise pulling the oil filter and changing the oil at the same time.

But be warned, these gauge are just dummy lights. Mine has had this problem since new and I have never bothered too fix it. If you want too know your real oil presser you will need a real gauge.

Oil sending unit replacement

Sal said:

Depends on the year of the engine. 97-98 had intake problems that would cause dumb stuff like hydrolocking and such.

99+ are good. I have seen many at 200,000 plus with little maintance. I have a 2000 model that runs great.

The sending unit is a very common problem with these trucks. It is located near the oil filter on these engines. The part is about 10 bucks. You will loose some oil. I would advise pulling the oil filter and changing the oil at the same time.

But be warned, these gauge are just dummy lights. Mine has had this problem since new and I have never bothered too fix it. If you want too know your real oil presser you will need a real gauge.

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I replaced the oil sending unit and it solved the bouncing and low indications from my oil pressure guage. It also stopped the oil pressure light from comming on occasionally. I attached a few pics that may help others with a 97 Ford F150 4.2l.
I'm thinking that the sending unit went bad because I used an engine flush as a last resort to stop a ticking valve. The flush stopped the ticking valve, but at the expense of a $15 OSU. I'm OK with that.

Haha
Pray that a cam follower didn't fall off. Lol


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4.2s are not OHC. They have rods.

Crap. I was thinking of the 4.6.


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