Do you notice some puddles of oil on the ground, particularly when the engine is running? That’s probably one of the most obvious symptoms of a rear main seal leak. So don’t be shocked when a mechanic tells you that the oil is leaking from the rear main seal.
The rear main seal is that critical of a seal on your car that you don’t expect it to leak around unless you’re dropping your engine or transmission because to get to the rear main seal, you need to dissemble the engine or transmission first before you can access it.
The most common cause of the rear main seal failure almost always comes from either inside the engine or at least on a part closely connected to the engine.
That kind of news can ruin your day because the rear main seal replacement is among the most expensive repair jobs to do on your vehicle, and it’s also one that many people fear the most. It can set you back anywhere from $600 to $900 or more at a dealership.
Fortunately, there is a shortcut to it. But before you lift your hands in panic, note that it is by no mean a permanent fix, which explains why we are taking a long look at the signs of a rear main seal leak and how exactly to replace it.
What is a rear main seal?
What is a rear main seal and how does it work? The rear main seal resides at the rear of the engine between the engine and the transmission, keeping the end of the crankshaft from leaking.
The repair is costly because, most of the time, the transmission must be removed or the engine dismantled.
On front-wheel cars, the engine is usually mounted diagonally, so the rear of the engine is opposite side number one with the idler pulleys, tensioners, and serpentine belt.
Engine oil leak from the rear crankshaft seal is tough to diagnose, unless you’re a gearhead like me, because the oil typically drips from where the transmission connects to the engine and drips elsewhere, like the crankcase.
The rear crankshaft seal is typically made of silicone or rubber. The seal wears out over time due to road salt corrosion, crankshaft forces from rotation, and other environmental factors.
If you have a rear main seal leak, you are in big trouble. You risk complete engine failure.
Rear Main Seal Leak Symptoms
Because of the location of this seal, it is difficult and complicated to recognize and fix an oil leak.
Just as with every other moving mechanical part or component, there will be signs and symptoms alerting the driver of a defective/lost rear crankshaft seal.
#1. Puddles of oil.
The major sign of a rear crankshaft seal is oil puddles on the driveway or garage floor. The oil puddles can be observed either while parked for a long time; or while driving.
Oil can leak from different parts of an engine so it’s advisable to diagnose from where exactly the oil is leaking before concluding it’s the rear main seal.
#2. Smoke from under the vehicle.
A leaking rear crankshaft seal will most times drip on the exhaust and lead to smoke from under the car.
If smoke is coming from under the car, you should be able to tell that smoke is not from the tailpipe. Smoke from the tailpipe means that the engine is burning excess oil. Not a rear crankshaft seal leak.
#3. Accumulation of dirt and debris.
Oil leaks make up an adhesive. When you have a rear crankshaft seal leak, dirt and debris from the driveway stick to places covered with oil; accumulation of dirt and debris is one of the early signs of a component leakage.
Simply put, if you see the accumulation of dirt and debris between the transmission and engine, it’s a sign of a leaking rear crankshaft seal. You need a rear main seal leak sealer or additives to stop it leaking at this point.
#4. Quick Oil Reduction.
If your automobile has started losing considerable amounts of oil without apparent damage, it’s most likely a result of the seal in the rear main carrier behind your crankshaft. A rear main seal leak is caused by all manner of things; including wear and tear of the seals themselves.
You see it on your routine checkups with dipstick oil level coming down to low level. Noise while you a driving, and it keeps blinking. The best do is to check your car oil in the morning before going everywhere.
What causes the rear main seal leak?
Many other factors can cause the rear main to leak. Let us look at factors that can deform and deteriorate the rear crankshaft seal.
#1. Engine oil condition.
Even the wrong engine oil or level of engine oil present in your engine can cause the rear crankshaft seal to leak.
Most engine oils these days contain some chemical additives that can affect all the seals in your engine.
Irregular oil change will lead to deteriorating seals. The seals deplete over time, together with other buffers in the oil. The inner lip driving on the crankshaft dries off and becomes stiff and useless in sealing the crankshaft.
#2. Worn main bearing.
A worn out or bad engine main bearing causes the crankshaft to dangle inside the bearing leading to stretching and moving of the rear crankshaft seal while the engine is running.
That is, your engine is suffering from worn main bearing. We all know the importance of main bearings, in case this is true, you should ready yourself for lots of work to rebuild your vehicle’s engine and replacing many of the bad parts, the rear crankshaft seal inclusive.
#3. Crankshaft condition.
The rear crankshaft seal lip rides directly on the crankshaft. That is, the crankshaft surface that the inner seal drives along is very crucial.
Any imperfection or wear on the crankshaft can lead to a leak. A sleeve kit can be installed on it to restore the seal surface.
#4. Clogged or defective PVC system.
As the inner lip of the rear crankshaft seal rides on the shaft when it is forced to do so by excessive pressure of crankcase, it will pull the seal on to the crankshaft and ultimately cause it to swell, likely resulting in an oil leak.
What causes too much pressure of the crankcase? A faulty or blocked positive crankcase ventilation (PCV) will increase pressure in the crankcase and may cause to blow out the seal.
Also, if the engine is of the turbocharged or supercharged kind, excessive blow-by from defective or worn piston rings can increase the pressure of the crankcase and have an effect on the seals, causing oil leaks.
#5. Alignment Problems.
Whatever your transmission is auto or manual, problems on the input shaft of the transmission or broken flex plate can strain the rear crankshaft seal.
Always check in an automatic the flex plate for damage. When it is a manual transmission, the input shaft.
#6. Seal coating.
Some rear crankshaft seal has a polytetrafluoroethylene coating and is employed to be installed dry.
It will transfer a layer of PTFE to, which the inner lip will sit on. The PTFE prevents wear and seals pretty much better than Viton and silicones. If by any means the seal is coated with oil at the time of installation there will be an effect on the sealing making it leak in a short time.
How to Replace the Rear Main Seal?
A rear main seal leak can be a disaster for your car. If you’re losing oil in that area, you have to quickly fix that leak before it can wreak havoc upon your engine.
You do not need to spend a lot of your time if the seal shrunk or slightly deteriorates, or deformed due to irregular oil change. If that’s the case, the seal does not need to be replaced; it just has to be reconditioned.
It is no news that engine seals deteriorate in a long period of use due to the oil acidity, heat, and several other related issues usually due to poor maintenance.
In such a case, the rear main seal stop leak is needed to recondition the seal and last for a few thousand miles.
To recondition the rear main seal, get a blue devil rear main sealer. This item is uniquely formulated to stop the rear main seal leak.
It does this by restoring rubber gaskets and seals, it’s also a good repair for the timing cover leaks, and it’s harmless to be used for both gas and diesel engines.
It’s also compatible with both synthetic and conventional oils. Bear in mind that this will not work if you have chunks, tears, or holes on the seal.
No item can fix a big chunk or a hole on a rubber seal. So if you have a massive hole in the rear crankshaft seal, follow the below steps.
Disconnect the battery
You have to disconnect the negative battery terminal in this step since you are required to remove the starter. To prevent getting a jolt or short circuit, disconnect the battery terminal.
Remove the transmission
Some vehicles need the removal of some vital components like an exhaust system, or a driveshaft in order to remove the transmission. Remove whatever is preventing you from removing the transmission.
If you are working on an automatic vehicle, you will have to disconnect the torque converter from the flex plate. Lose the torque converter bolts one at a time with the proper size socket and ratchet handle.
After losing the first bolt, turn the engine clockwise until the next bolt presents. Lose the second bolt and do the same for the rest of the bolts.
Remove flywheel
If you own a manual transmission vehicle, you will be required to remove the clutch and the flywheel. If automatic, then remove the flex plate.
Remove rear main seal bolts
Now that you have removed the transmission, the clutch and the flex plate, the next thing is to remove the rear main seal. You may sight some crankcase bolts linking the crankcase to the rear crankshaft seal housing, break free and remove these bolts.
The rear crankshaft seal housing has some 10mm or 12mm bolts attaching on the back of the engine block. Take off these bolts and remove the seal housing. The housing may be stubborn to come off; stick a Flathead screwdriver in it and pry it off.
Remove the rear crankshaft seal
The rear main seal itself may also be a little difficult to come off the housing – you may have to pry it off and remove it from the housing with some effort.
Compare the new seal
Now you need to put the old and new seals together and compare them – make sure the new seal’s inner and outer diameter match the old.
Install the new rear main seal
Carefully clean the seal housing. A gasket scraper comes in very handy in scraping away the old seal debris on the housing. Place the seal into the housing and carefully hammer it into place evenly.
Don’t forget to coat it with oil before finishing the installation. Once you do, it doesn’t hurt to run a light bead of sealant on the surface.
Install the rear main seal housing
Bolt the seal housing into place, bolting the crankcase bolts as well. Now you are ready to put everything back together, using the reverse of the above process to carry out the reinstallation.
FAQs.
Q: Is a rear main seal leak serious?
If there is a slight puncture in the seal, the crankshaft rotation will work against it and cause it to tear open more and leak out a lot of the engine’s oil and reducing the oil to a dangerously low level.
And a dangerously low-level oil could cause friction and wears inside the engine, resulting in engine Knocking.
Q: How much it cost to replace the rear main seal?
Sea whatsoever the material it was manufactured of, still, it is a critical seal designed to keep oil where it should be, and commonly needs replacing when it shrinks or degenerates.
And the standard costs to replace rear mains is about $600-900 with a fee of $550 to 820 conducting service out of total replacement charge.
Q: How long does it take to replace a rear main seal?
All of that could take a long time and some labor. All we told you beyond was that part one of a rear main seal replacement was pulling the transmission out. Later on, some vehicles, you would have to pull the whole engine out.
Now you have a good idea of how much time you would have to expend just to pull a ‘seal’.
There is a small point there; the prior would also have to diagnose the vehicle to know what’s causing the oil leak. The actual seal would cost you virtually nothing. But the extracting cost is just dropping behind the state!
And that is why is quite expensive for a professional mechanic to fix it and would charge heavily to replace the seal in your car. Most dealership and auto garage shops will.
Q: Does the rear main seal stop the leak work?
Yes, it works perfectly fine on a shrunk or degenerated seal, though it is specially formulated to stop rear crankshaft seal leaks ACME also works perfectly on other engine oil leaks, including on the O-rings, camshaft seals, timing cover seals, and other seals.
Final thought
With everything else considered, you should always keep an eye out for rear main seal leak symptoms and get to it as soon as you see that particular spot leaking. Unless you’re a gearhead, replacing a rear main seal might be a daunting job for you.
Nonetheless, as challenging as the process may be, it is by no means impossible. With the right dedication, you could do it on your own. In your attempt to cut down on repair costs, always prioritize your safety.