Just got a 1994 F150 for $620. First the brake lines, then the springs, the wheels won't come off, and now I have no oil pressure? Well I guess I got what I paid for. My oil pressure gauge goes down to 0 when at idle and back up to normal when I'm driving or when I rev up the engine. Anybody have any idea whats going on? I have a feeling its just the gauge going bad cause my speedometer also acts up from time to time too, but I don't know.
check the connections on the pressure sending unit, and also make sure your grounds are in good shape, if possible hook a mechanical guage up to see how much pressure you really have, the stock guages arent that reliable
If it turns out your rocker just popped off, fix it. Then try that Chemtool cleaner in the oil like I said to break that gunk loose. Put 10w-40 in instead and don't forget a new filter. I bet the pressure comes back up.
I'm gonna take off the rocker covers tomorrow and take a look at it. I found out that the guy I bought it from actually did have someone change his oil every 3K miles and that sticker was old. So now I'm trying to find out exactly what went wrong and why I still have no pressure even after replacing the oil sending unit. Remember this oil pressure problem happened 2 days after I changed the oil.
Someone correct me if I'm wrong here but all oil in these engines passes through the oil filter, right? Now, if you changed the oil and dirt and gunk broke loose, it may have plugged the oil filter and that could cause a large restriction.
filters have a bypass valve, so if they are completely plugged, the oil will bypass the filter and just not be filtered
if a rocker has "fallen off" it will not really affect the oil pressure, you would have one dead cylinder
it sounds to me like you have wasted the main, rod, and/or cam bearings....the pump produces oil flow, restriction to that flow is what creates the pressure, and the bearings are what creates that restriction...if the gap is too large, then there is less restriction and the oil just falls out without building up to any pressure...the pressure raises with RPM because that is also increasing the speed that the oil pump is turning, which means it is now pushing a higher volume of oil, which cant fall out of the gap between the bearings as fast, so it creates some restriction
sounds like your $620 beater needs a new motor, or a rebuild..or you can go the cheap route and just rol some new bearings into it without doing any machine work, or do a crank kit...got several options, anyway
What engine? I have a 4.9 that does the same thing, the reason it drops to nothing is when it senses less then 5 psi, it drops to 0, kinda like an idiot light but in a gauge. I have ran my for 10k so far, and it still makes no noise, and ran great until I broke something else. As long as you aren't getting noise from the engine I wouldn't worry about it.
Its a 351. It knocks now and it burns a little bit of oil, but I think its just one of the rockers that popped off. When I first start the truck I have full oil pressure then after about 5 minutes it warms up and the gauge drops to 0. The pressure also goes back up when I give it gas.
Put in a new Wix filter. Change your oil to 20w50 Valvoline. Put in 2 cans of Restore for V8 engines. Take it out for a 1hr drive. Be sure to put 1/2 quart less 20w50 when you change it.
Park it next day you should have 30+ pressure. I had a 69 302 with Zero pressure, have a fresh 302 on the stand for it. Still driving it everyday, & I run the piss out of it.
I took the motor out of the truck and tore it down since it was knocking, and found out the oil pump seized up, and it spun all the bearings. Gonna be a $500 rebuild. That's just what I need.
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