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1986 Bronco 302 and 1996 Bronco 351
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Discussion Starter · #1 ·
I have a 1996 bronco 351. It had a pretty heavy oil leak. Replaced rear main seal and oil pan and oil pan gasket. Leak stopped— until it got cold at night. Now, every time temperature dips below freezing, it leaks oil. Above freezing? Does not leak oil. Something is clearly expanding or contracting and forcing oil out of somewhere when temp dips below 30 at night. Any ideas?
 

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If it is not a Bronco, it's just not worth driving.....
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1,900 Posts
Can you tell what area of the engine the leak is coming from? Its kinda hard to give you some pointers with the information given. Does it leak oil with the engine off or just while running?

See if you can locate a oil trail on the engine area. Might be coming from the valve cover gaskets or could even be the timing chain cover area. Could even be from the oil pan gasket that was replaced.
 

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Registered
1986 Bronco 302 and 1996 Bronco 351
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43 Posts
Discussion Starter · #3 ·
Yes it is coming from right where the oil pan meets the transmission. It only leaks when it is not running and it is below freezing out.
 

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2,016 Posts
I replaced my rear main seal a few years ago and not long after it was leaking again. I guess I should have used a shaft repair sleeve. Unfortunately I didn't know about the sleeve kit at the time but I read about it a couple years after the fact on this forum.
 

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Yo gentbronco,
Following from 1996 All F-150, F-250, F-350, F-Super Duty and Bronco Vehicles Equipped with 4.9L, 5.0L, 5.8L or 7.5L Gasoline Engines, and 7.3L Diesel Engines Workshop Manual @ http://www.diesel-dave.com/vehic/manual/stj/s
Section 03-00: Engine, Service
SERVICE PROCEDURES
Engine Oil Leaks
When diagnosing engine oil leaks, the source and location of the leak must be identified prior to service.

Fluorescent Oil Additive Method
  1. Add Rotunda Gas Engine Dye 164-R3705 or equivalent to the engine oil. Use 29.6 ml (1 ounce) of fluorescent additive in all engines.
  1. Clean engine with a suitable solvent to remove all traces of oil.
  1. Run engine for 15 minutes.
  1. Stop the engine and inspect all seal, gasket and galley plug areas for leaks using Rotunda Oil Leak Detector 164-R0756 or equivalent. A clear bright yellow or orange area will identify leak. For extremely small leaks, several hours may be required for the leak to appear.
  1. NOTE: For minor gasket leaks tightening the retaining bolts may resolve the problem.
    Service all leaks as required.
Next up to bat is;
Section 03-00: Engine, Service
1996 All F-150, F-250, F-350, F-Super Duty and Bronco Vehicles Equipped with 4.9L, 5.0L, 5.8L or 7.5L Gasoline Engines, and 7.3L Diesel Engines Workshop Manual​
SERVICE PROCEDURES
Leakage Points
Examine the following areas for oil leakage.
Underhood
Valve cover gaskets (6584)
Intake manifold gaskets (9439)
Head gaskets (6051)
Oil bypass filter (6714)
Distributor O-ring
Oil level indicator (dipstick) tube connection
Oil pressure sensor (9278)
Cup plugs and/or pipe plugs at end of oil passages

Under Engine, with Vehicle on Hoist

Oil pan gasket (6710)
Oil pan front and rear end seals
Crankshaft front seal (6700)
Crankshaft rear oil seal (6701)
Engine damper keyway (damper to damper bolt/washer interfac
 
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