Do I panic? - Rear main oil leak.
 

My special coupe just sprung a rear main oil leak. Do I panic, or just keep oil in it as I drive the car?


Bill Harms
Walworth, New York.

Re: Do I panic? - Rear main oil leak.
 

Sometimes it is the front, and it trails back as you travel down the road. Wipe everything clean, push it onto clean pavement, start it up and slide under it.

From there you can asses. How many miles on engine? lightened flywheel? I take it that it leaked zero before? Are you a member of a local Model-A club chapter?

Re: Do I panic? - Rear main oil leak.
 

Is it leaking a 1" puddle or a 6" puddle? If a 1" puddle, that is normal. If a 6"puddle and it happened suddenly and is coming from the rear of the engine, the rear main babbit bearing has probably cratered and you need an engine rebuilt.

Re: Do I panic? - Rear main oil leak.
 

Good afternoon...Can you please tell us how big the spot is or photograph it with a tape measure beside it. You might check to see if your breathing tube is clogged with something...the pipe that you use to add oil...I have found paper towells in those pipes in the past...Ernie in Arizona

Re: Do I panic? - Rear main oil leak.
 

Or could just be over filled with oil. Make sure the dip stick is all the way in and check the level. Oil spreads, so a small puddle can turn into a large one fairly fast.

Re: Do I panic? - Rear main oil leak.
 

I do not know how may miles are on the engine. I know it has been rebuilt at least once, possibly twice.

Don't know about the flywheel yet.

That is correct, no or minimal leak out of this spot before. It started all of a sudden.

Yes, and I have been in contact with a Model A mechanic in the local chapter about this problem. He just told me to monitor the leak.

My concern is the suddenness of the leak and wondering if there is not something more going on.

What is disheartening to me is that I have had an engine sputtering issue and just replaced a condenser which fixed the problem. No sooner was that fixed, them this issue popped up.

Bill
Walworth, NY

Re: Do I panic? - Rear main oil leak.
 

It is a fairy good sized leak after sitting just a few minutes. I have not measured it, but I guess it is at least 6 or 8 inches.

The doggone engine runs as smooth as silk, and the compression on all four cylinders is just below 75 psi each. It has an aluminum cylinder head (high compression.) I imagine the compression ratio is about 5.5 to 1. The engine is rather peppy.

So, I am loathe to take the engine apart if it is a simple leak, or is there such a things as a simple leak?

As noted elsewhere, a local Model A mechanic told me to take a "wait and see" position on this issue for now. He said to just make sure it has enough oil and put down an oil pan or doggy pads when parking it.

Bill
Walworth, NY

Re: Do I panic? - Rear main oil leak.
 

Actually, I checked the oil earlier this evening, and it was above the Full mark on the dipstick. It is possible that there is too much oil in the crankcase. We last changed the oil about 500 miles ago with the prescribed 4.5 quarts. Is that too much? Coincidentally, I was going to change the oil again this week,

Bill

Re: Do I panic? - Rear main oil leak.
 

Next time when you drain the oil, only put back in 4 quarts. The conventional wisdom is that the engine retains 1/2" quart in the dipper tray and valve galley, but I think it is more particularly if the oil has not drained down out of the valve galley fully. I have gotten into the habit of adding only 4 quarts on an oil change and it shows halfway between Full and Low on the stick. If I add 4 1/2" quarts, it doesn't come out the rear main so much as it slobbers out the front seal and runs back on the engine, making a mess. Yeah, I need to address that.....As they say, "Your Mileage May Vary."

Re: Do I panic? - Rear main oil leak.
 

Re: Do I panic? - Rear main oil leak.
 

Bob is spot on
Also shocks leaked or did very shortly in use

Re: Do I panic? - Rear main oil leak.
 

Four quarts for a stock engine. Change every 500 miles.

Re: Do I panic? - Rear main oil leak.
 

I have a drip pan under the radiator, the transmission/engine (big pan) and one under the rear. I drive the car very often and enjoy it. I've driven from NJ to Gettyburg in 2017...JUST DRIVE IT. Check the fluids and enjoy it. I may suggest a lot of folks here use Valvoline 20/50 Racing Oil ($8.00 a quart). The higher viscosity when hot may help. They all leak, until they are empty. What are you going to rebuild an engine to put 1,000 miles on it.....fill it up it's cheaper and just fine. One last point you should wipe it all down and start checking bolts, my valve cover was leaking pretty good and so was the oil pan. Watch those oil pan bolts, very weak...not much pressure please or snap. Check all the rear banjo bolts they then to loosen around the area of the driveshaft. Relax man you finally got it drivable....drive.

Re: Do I panic? - Rear main oil leak.
 

The instruction book says "up to the F" drain some or don't add any more and see if it finds a level it likes or the level gets to "L"

Re: Do I panic? - Rear main oil leak.
 

Based on what you said, at the most I would change the oil pan gasket set. Ya have noting to lose by getting under there with a 1/4 ratchet and an extension and making sure the bolts are snug. I kind of think you are fine. Forget about the stains on the driveway, and start watching the dipstick in the mornings before you fire it up. The spots can be deceiving. I use a piece of cardboard, and toss it in the trash every so often, or you can simply take it out back and light it off.

Re: Do I panic? - Rear main oil leak.
 

Well, I am not sure what is going on. The amount of oil leaking has subsided, and is down to almost nothing. There is still a bit coming out, but now as bad as before. Interestingly, the oil level in the crankcase has not gone down that much. I imagine that when we replaced the timing gear, the crankcase oil seeped out into the rear housing. And when we started to drive it and it was on level ground, it started to gush out. Let's hope this is the case anyway.


What was disturbing to me was the suddenness of the leak and the volume. Since it has apparently subsided (as of yesterday) I am not going to worry about it.

Re: Do I panic? - Rear main oil leak.
 

Yes, someone here in the local Model A Club Chapter suggested the Valvoline racing oil at 50 weight. I will also try putting in four quarts at the next oil change.

Re: Do I panic? - Rear main oil leak.
 

Has anybody here mentioned the drain tube on the rear main bearing cap. Those have been known to beak off or unscrew themselves.

Re: Do I panic? - Rear main oil leak.
 

Okay, from where does one get a drip pan?

Re: Do I panic? - Rear main oil leak.
 

Do not panic.
before you worry about a rebuild,
check the main bearing clearances- too much on the rear lets oil out.
then you can get the new pan gasket instsalled.

Go-no-go method with aluminum foil works better and easier than Plastigauge for bearing clearance. (check the rods too!)

Restorer magazine Mar/Apr 2002, pages 16-18 has the ultimate procedure for leak-free pan gasket install