Death to a motor...
RandomTask
02-10-2005, 11:59 AM
Yesterday while driving my 2M4 fiero I was sitting at a stoplight. Im pretty anal about checking my gauges so I saw it as soon as it started happening. My oil pressure kept rising from 50-60psi at 1k rpm, up to 120 psi at 800 rpm. I knew that wasn't good, but I had to get home from school, so I kept on it. About 1 mile from house, the needle was buried all the way down. (Passed 120) and it started making a wierd sound. It wasn't the grinding sound most people are familiar with, rather the type of grinding when your on a mill cutting into steel. I think I spun a main but does anyone have any other suspicions? I'll be sure to post pics!
curtis73
02-10-2005, 01:46 PM
I wish I could offer an answer... I anxiously await knowing what happened, but I just wanted to sympathize.
Even if the pump spring froze, I don't think the pump would be capable of supplying 120 psi. I would drain the oil and see if it tels you anything. Metal shavings? Are they ferrous or not?
Not too familiar with the underside of those Fieros, but is it possible to drop the pan with the engine in the car?
If it were me, I'd be on ebay shopping for a Northstar to put in it. :)
Even if the pump spring froze, I don't think the pump would be capable of supplying 120 psi. I would drain the oil and see if it tels you anything. Metal shavings? Are they ferrous or not?
Not too familiar with the underside of those Fieros, but is it possible to drop the pan with the engine in the car?
If it were me, I'd be on ebay shopping for a Northstar to put in it. :)
RandomTask
02-10-2005, 10:03 PM
Oh northstar, where art though?
That would be a fun swap, I think I want to make it my next, but I need a fiero/car for a daily driver, the other is for beating the crap out of. If I can find an inexpensive northstar local, or semi-local (va area) I'd be more than willing/anxious to drop it in... I'm going to dig into it hard saturday... I just hate that now , im back to horrible gas mileage on a tiny gas tank... =P
That would be a fun swap, I think I want to make it my next, but I need a fiero/car for a daily driver, the other is for beating the crap out of. If I can find an inexpensive northstar local, or semi-local (va area) I'd be more than willing/anxious to drop it in... I'm going to dig into it hard saturday... I just hate that now , im back to horrible gas mileage on a tiny gas tank... =P
Schister66
02-12-2005, 06:24 PM
Alright here's what happened.
An oil pump is a positive displacement pump, meaning that it is going to pump oil if it is turning, and the higher the RPM, the faster it turns, and the faster it turns the more it oil it pumps (more pressure).
Oil pumps are capable of pumping 1000+psi, but they don't because oil filters can only hold 120psi or less and other engine components can only handle so much pressure too. Therefore the pump has to have a way that it can pump less than 120psi and still compensate for accessories that need more oil. (If you were to install an oil cooler or something that took pressure away, the pump makes enough pressure to compensate for the loss in pressure)
Ok got that part...?
There is a little valve in the oil pump called the bypass valve that allows the excess pressure to escape being pumped so that the oil pump doesn't pump too much pressure and wreck something. Now if that were to get clogged, your oil pump would pump all of the pressure through the system and that's why the guage reads excessive pressure.
This is actually a simple fix in most cars. All you have to do is drop the oil pan and replace the pump or clean out the bypass.
BTW, if you spin a main bearing, the oil pressure will fall because there is an excessive gap between the thrust bearing and the journal on the crankshaft which will allow the oil to fly everywhere from the oiler hole on the crankshaft journal.
The reason the pump wouldn't compensate for the loss of pressure is that it is such an extreme loss of pressure that spring in the bypass hole wouldn't be able to close enough to keep all of the pressure in the system. The spring on the bypass can only flex so much.
I hope this helps.
An oil pump is a positive displacement pump, meaning that it is going to pump oil if it is turning, and the higher the RPM, the faster it turns, and the faster it turns the more it oil it pumps (more pressure).
Oil pumps are capable of pumping 1000+psi, but they don't because oil filters can only hold 120psi or less and other engine components can only handle so much pressure too. Therefore the pump has to have a way that it can pump less than 120psi and still compensate for accessories that need more oil. (If you were to install an oil cooler or something that took pressure away, the pump makes enough pressure to compensate for the loss in pressure)
Ok got that part...?
There is a little valve in the oil pump called the bypass valve that allows the excess pressure to escape being pumped so that the oil pump doesn't pump too much pressure and wreck something. Now if that were to get clogged, your oil pump would pump all of the pressure through the system and that's why the guage reads excessive pressure.
This is actually a simple fix in most cars. All you have to do is drop the oil pan and replace the pump or clean out the bypass.
BTW, if you spin a main bearing, the oil pressure will fall because there is an excessive gap between the thrust bearing and the journal on the crankshaft which will allow the oil to fly everywhere from the oiler hole on the crankshaft journal.
The reason the pump wouldn't compensate for the loss of pressure is that it is such an extreme loss of pressure that spring in the bypass hole wouldn't be able to close enough to keep all of the pressure in the system. The spring on the bypass can only flex so much.
I hope this helps.
RandomTask
02-14-2005, 05:14 PM
Excellent, I was going to do the motor today but have a ton of studying instead. It will defintely be something to look into and I'm very curious to see if thats the actual cause. The reason I listed as spinning a main is the noise that its making. Again, I'm taking all this as new information and trying to learn as much as I can with this diagnosis. Thanks and I'll keep you posted!
MagicRat
02-14-2005, 07:01 PM
Good post from 66.
I have had the bypass valve stick closed before in small block chevys. The oil filters will rupture long before any other damage is done. However, you lose ALL oil pressure instantly when that happens so subsequent damage occurs rapidly unless you shut off the engine.
Now, I aqm speculating here, but if the valve got partially stuck, the increased pump load mught overstress the cam/distributor/pump drive causing noise. Specifically the camshaft gets shoved 'forwards' (away from the transmission) in the engine block. There is a cam 'button' intended to take this load, and when overstressed, can make this grinding noise. It might also be the cam drive chain or gears getting slightly out-of-line as the cam get moved out of place.
Finally, are you sure the gauge is accurate? These electric gauges read higher as the electrical resistance in the circuit falls. If the sensor fails or there is a short in the wiring, you can get a false reading. You could install a mechanical gauge in place of the stock sender and measure it that way.
I have had the bypass valve stick closed before in small block chevys. The oil filters will rupture long before any other damage is done. However, you lose ALL oil pressure instantly when that happens so subsequent damage occurs rapidly unless you shut off the engine.
Now, I aqm speculating here, but if the valve got partially stuck, the increased pump load mught overstress the cam/distributor/pump drive causing noise. Specifically the camshaft gets shoved 'forwards' (away from the transmission) in the engine block. There is a cam 'button' intended to take this load, and when overstressed, can make this grinding noise. It might also be the cam drive chain or gears getting slightly out-of-line as the cam get moved out of place.
Finally, are you sure the gauge is accurate? These electric gauges read higher as the electrical resistance in the circuit falls. If the sensor fails or there is a short in the wiring, you can get a false reading. You could install a mechanical gauge in place of the stock sender and measure it that way.
Schister66
02-15-2005, 08:17 PM
How long did the guage read more than 100psi?? If it was more than say 15 sec, i would wager that the sending unit or the guage are off somehow. I would check the oil pump and then if that isn't the cause, i would repost and we'll find a different solution. For now, i would check the bypass valve in the oil pump.
RandomTask
02-15-2005, 11:08 PM
It fluctuated between 80-120 psi, increasing with the RPM's for the (approx) 5 minutes it took to get me home. If it were a short, I would imagine it to draw as much current as it could until a fuse blew, am I correct? I really haven't had the time to tear it apart over the last couple of days but am trying to set aside some time this sunday. 66, your help has been extremely informative and is appreciated! (And I still love you curtis...)
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