Help! First Foxbody, Having Mystery Oil Leak

bryant91gt

New Member
Mar 20, 2014
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My name is Austin and I'm 19 years old. I recently bought an 86 mustang gt with a 91 mustang gt engine in it, 5.0 HO motor. Bought it in Kentucky and drove it back fine. After driving the car for a bit and looking around, Ive kinda found the few things the guy had Jerry Rigged. For example, a COMPLETELY covered water pump in JB Weld, my gas tank fell because of poor support from THICK GAUGE SPEAKERWIRE holding it up, and lastly some lazy wiring. But anyways, about a week ago I noticed that oil was starting to pool up on the crevices and little valleys on top of my motor. Leaking from behind my intake and covering the back end of the motor onto my transmission and exhaust. It doesn't leak a whole lot, it has just started to gather the more I drive it. Therefore causing it to smoke when motor is hot. I bought intake gaskets and valve cover gaskets, because that what I THINK it is. I'm new to the 5.0s and know nothing of their common problems, so I would love to hear any advice or tips on what could be wrong and what I could do to learn and make this right. ALSO, sometimes my car idles high at random times. Between 1100 to 2000 rpms. Not sure if its a serious problem or what. Like I said, I'm new to these cars, as I was always a Mopar guy. If anyone could help me out, it would be greatly appreciated! Please and thank you!
 
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At the rear of your lower intake is your pcv valve. Underneath it, inserted into the hole in the lower intake is a screen. Sounds like this could be plugged up or even non existant. They can be cleaned out with carb or break cleaner.

Pop the pcv valve out by pullin straight up on it. Shake it, if it rattles its still good and can be reused.

Theres also a rubber grommet that should be there that the pcv valve itself sits into. These also wear out and loosen up. They can be picked up at any auto parts store in the vacuum tubing or help section.
 
Thank you guys! I went ahead and bought the PCV valve along with the grommet just in case I needed them before I messed with it. Also, bought myself a water pump to install as well because of the rigged old one was just an accident waiting to happen. But now, my car is making a new sound. I installed a 190 degree thermostat the other day because my car had no heat. It was working fine, blowing heat and the temperature was even perfect. I got in it today to drive to the parts store and my car was making this weirs bubbling liquid sound coming from behind my vents but mainly on the passenger side. I stopped, checked underneath the hood and seen some coolant leaking from close to my thermostat. Not much, but it was noticeable. I don't know if this is a serious problem or what.
At the rear of your lower intake is your pcv valve. Underneath it, inserted into the hole in the lower intake is a screen. Sounds like this could be plugged up or even non existant. They can be cleaned out with carb or break cleaner.

Pop the pcv valve out by pullin straight up on it. Shake it, if it rattles its still good and can be reused.

Theres also a rubber grommet that should be there that the pcv valve itself sits into. These also wear out and loosen up. They can be picked up at any auto parts store in the vacuum tubing or help section.
 
Ill bet you didnt seat the thermostat down into the groove properly, or installed it upside down
I checked and the thermostat was installed correctly. Installed a new water pump about two weeks ago. Drove it and it overheated and got up to 250 degrees! Turned it off and let it cool down. Took out my thermostat because it was sticking and it ran better after. I also found out that my oil leak was due to my valve covers not being tightened and finding that the recent owner had used home appliance silicone instead of a gasket. But I'm still having the idling problem. When it warms up, it will drop to 1000rpms and if I drive it for 10 minutes it will be fine, then start again at random times. Was told it might be throttle position sensor? And it stalls sometimes as well, could be MAF sensor?
 
Pulling codes would be a good idea just to see where you stand, as far as idle problems, they are common with the 5.0. The first place to start is the free stuff like cleaning the IAC valve ( cylindrical thing on the side of the throttle body) it has a plunger inside that can get gunked up and cause idle issues.
 
2 things for random idle surge...

pcv: did you replace the screen cage under the pcv valve and grommet,as madspeed advised? if not replacing pcv has no impact it needs to breathe through that screen

intake/throttlebody/MAF: get a can of crc or similar throttle body cleaner. pull the air tube, take off the MAF unplug and bolts holding bracket (maf is the metal piece between the filter and the throttlebody) spray the heck out of it and let cleaner run out of it and evaporate... now spray the throttlebody inside really well, ive done TB with car running and not running...just do what cleaner says do on that...

from what youve described i highly doubt previous owner did this process, typically anytime you have idle surge this is the place to start... pulling codes also helpful in knowing what the computer sees such as vaccum leaks, faulty sensors etc

thermostat. place it in boiling water, with a thermometer test water temp, should start opening near the designated temp ie 190 degrees if not its faulty if it does recheck how you installed it can be installed backward and block water flow also if ir has a little tab be sure its in the groove at top... a sticky gasket helps hold the thermostat in place making install easy as well...
 
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You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 134,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
 
check your passenger side carpet near the firewall for coolant. The heater core for your interior heat is behind the dash on the passenger side, and when they leak (possibly from overheating) they drip coolant onto the floor in the car. That could be the noise you heard.