freebird87

I have a 87 trans am 305 tpi, and I was wondering what would cause negative crankcase pressure. Its been like that for a long time now and the car was running super strong. The other day i was driving down the road and suddenly lost oil pressure and started overheating, would the case pressure have anything to do with it its my daily driver so if anybody could help it would be much appreciated.

vetteoz

iTrader: (13)

What is negative crankcase pressure? How do you know you have it?

flaming-ford

iTrader: (7)

negative crank case pressure is no big deal and in fact is engineered to be that way, if memory serves me correct.

some have even used vaccumm pumps to increase this negative crankcase pressure. Theory behind it would be better ring sealing for the most part i beleive ,but don't quote me on it.

as for the theory behind it, im pretty spotty, so i'll let someone else speak up.

as for your car overheating it's probably a whole different scenario

think thermostat or electric fan operation if it does it again. make sure your fan or both of your fans are on and if your upper radiator hose is hot or cold (tells you if the t-stat) is open or not.

vetteoz

iTrader: (13)

The factory PCV system operates to create a controlled airflow through the crankcase to remove fumes and contaminants.I don't think it would be considered "negative" as in the system used on race cars for ring sealing.

freebird87

well thanks for the advice but i have my fans straight wired so that they stay on all the time and i'm not running a t-stat i still don't know what it is, the reason i know that i have it is because i can take out the pcv and the motor is sucking air in when it should be blowing it out.

vetteoz

iTrader: (13)

Are the lines hooked up the right way? Sounds like you have the vacumm supply or PCV on the wrong side. Disconnect the line on the other valve cover and see if it still has" negative " pressure

There is nothing in the engine to "suck" air in if the PCV is disconnected ; usually the engine pumps fumes out when hot

vetteoz

iTrader: (13)

Are you losing coolant?
Sounds like a blown head gasket or failed water pump

freebird87

its all right and yes its still sucking in air, it is confusing me greatly, i have a new water pump and im not losing any coolant. i've thought about all of this and still nothing...

vetteoz

iTrader: (13)

With nothing connected to either rocker cover you are still sucking air in?

AaronIROCZ

iTrader: (5)

Negative crankcase pressure will not have any effect on you loosing oil pressure or overheating. The lack of the thermostat will cause overheating issues. The coolant is flowing too fast for it to transfer heat properly from the engine and to the radiator. Check out this thread for further information.

https://www.thirdgen.org/forums/cool...l-true-no.html

vetteoz

iTrader: (13)

But how do you get negative pressure in the crankcase; where is the air going to?
Unless he has a intake gasket leak?

flaming-ford

iTrader: (7)

you need to run a restrictor plate at a bare minimum for the t-stat.

i'm thinking like the above check your vaccumm hose routing and check for vaccumm leaks.

AaronIROCZ

iTrader: (5)

In my situation I have aftermarket valve covers so I only have a spot for the pcv valve and the oil fill cap (plug in my case). I get engine vacuum since I have the pcv valve hooked up to the intake behind the throttle body and the other valve cover plugged off with the oil cap.

freebird87

yep sure is

freebird87

I see the theory but I've had the car for about a year now and it never had one in it and its always run 185 until the other day so I don't think that the t-stat has anything to do with it. When my oil pressure dropped is when it started overheating so it was just the friction. I'm just tryin to figure out what made me lose oil pressure still I know the pump only creates flow not psi so I'm once again stuck


and I forgot to put this earlier I do have a small intake manifold leak but its extremely small not even enough to make the vacuum gauge leak down

vetteoz

iTrader: (13)

That could account for the neg pressure; fumes are being sucked straight in to engine

AaronIROCZ

iTrader: (5)

If you think friction is what caused the overheating then my next step would be is to drop the oil to see if there is any metal mixed in it. If it ran for that long to cause the overheating due to friction then you might have other issues. How low of oil pressure are you getting, 0 or around 5-10ish. Either the oil pump has failed, the oil pump pickup tube has fell off or something in the driveshaft/distributor has failed. How does it run right now?? Any misses or white smoke??

freebird87

the oil pick up may be, but no white smoke and the car runs strong, I can turn it on and the oil pressure will stay around 10psi for 5 to 10 minutes then drops to zero, I took it down the road one time and it went to 14psi and no matter what the rpm was it stayed constant till it dropped all the way I let it sit for a min oil pressure went back up and I drove it home.

JakeJr

On another Forum, a guy posted about the same problem. Consensus is his oil pump pick-up fell off and is laying in the bottom of the oil pan.

One easy way to check is to drain the oil, then rap on the side of the oil pan and listen/feel for movement of the pick-up. Of course, you can always drop the oil pan to see what's going on.

Either way, you need to find out the cause before engine damage results.

Hope this helps.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!

freebird87

well bad news for me i dropped the oil pan today i've been held up or i would of done it sooner and i found piston #7 in the pan never heard a thing honest to God. so yea new motor coming soon hopefully. for all the help