Here's a list of almost all the potential leak places on a 4D56 engine, compiled by Yobbo over on the UK MDOC forum, with some edits by me because I just can't help myself.
First up: finding the actual source of the oil leak. The 4D56 can leak from many, many places, and the area where the oil ends up is not necessarily the source of the leak.
Step 1: Clean your damned engine. Steam clean, degreaser, Q-tips, whatever floats your boat, just get the outside spotless. Not just the oil either, you want to remove all the dirt and dust as that can trap the oil and help transport it away from the source of the leak.
Step 2: Drive it as normal, but after every drive check for oil. If you check often enough, you'll find the source of the oil before it dribbles down the engine.
Another great tip for those tricky leaks is spray foot powder. Clean the engine, then powder the suspect area: the foot powder will show up the oil leaks.
Now, on to the places it leaks, with the most common first:
*** OIL LEAK CHECKLIST ***
THE ENGINE BLOCK
- Rocker Cover Seal + Half Moon Seal + Rocker Cover Bolt Bungs. This is the most common place for oil to leak from.
*Fit a new:
Rocker cover gasket: MD050312
Retrofit an Alloy halfmoon (this permanently cures 90% of all leaks): MD372348 *or* a new original rubber halfmoon (and expect it to leak again in about a year): MD050536
Rocker cover bolt bung MD000523
* Clean up the surfaces with degreaser, then follow the directions in the workshop manual. The rocker cover bolts only need 6Nm of torque so don't go mad. I recommend grey, high-strength silicone, especially for fitting the alloy half moon (which should never need to be removed again).
- Oil Cap Seal
* The seal hardens with age. Sometimes flipping this can cure the leak, you'll need a screwdriver to remove the locking clip. New seal is MD311638, a whole new cap is MN143845
-Side cover by Injection Pump
Gasket: MD020239
Cover: MD020237
Bolts x2: MF140003
Bolt O-rings x2: MD020256
- Dipstick
* If it's loose expect splurting while the engine is running.
*** The Seals ***
* Its a patient job so have plenty of time, obtain some long nose pliers then drill a small hole and then thread a small self-tapping screw in and either pull it towards you or better yet lever it out against something.
You may need to bore a hole on the other side of the original to shimmy the seal out and obviously don't damage the inner surface of the seal mount when drilling as you'll hate yourself for eternity.
If the seal is being an absolute pig you can prize it out either by pulling with a hook and pick tool or with a small flat blade screwdriver and again, something like a bar or handle to lever against - it's okay to rest it on the outer edge of the seal mount.
- Camshaft Seal
* I wedged a breaker bar in between the arms ot the sprocket to loosen, a bit naughty but don't rest the bar on anything that could be damaged easily.
- Upper Balance Shaft Seal
- Lower Balance Shaft Seal
* For the Balance Shafts there is a custom tool pictured in the Tojo T-Belt Guide but no mention of dimensions; so you need a steel bar (Lx450mm,Wx35mm,Dx5mm), bore a hole big enough for your 12mm socket, and then drill 2x 6mm holes 30mm apart each side of the centre hole, you'll then need two M6 x 50mm ->HIGH TENSILE<- fully threaded bolts and nuts.)
- Crankshaft Front Seal
* If you've read the Tojo Guide then you'll understand that in order to get the bottom engine cover off you need to remove the crankshaft pulley! (Slow clap, Mitsubishi...)
There's talk in that guide of using a custom fabricated tool to unlock/lock the crank bolt but to be honest most people use the 'Breaker Bar Method' to get the bolt loose.
Also if the pulley is not budging once the bolt is off then a 6" Jaw Puller will do the trick.
On reassembly, tightening up the bolt is less trivial with the absence of a locking tool -
The best way I've found is the 'Flywheel Jam Method' by wedging a screwdriver or chisel in the centre bottom teeth of the flywheel and securing with lots of cable ties on the bottom subframe bar, but it's tricky as it often slips.
What I tried with success is to use a fat headed stone mason chisel to lock, and then put a trolley jack underneath to apply some pressure to avoid the slip.
Tiny bit of thread lock on the crank pulley bolt, and torque up to a max of 180Nm, job's a good'n!
- Crankshaft Rear Seal
* This requires seperating the gearbox from the engine so most of the time its left alone, I genuinely don't think it would be worth it replacing unless you had a severe leak from there, I definitely didn't do mine!
- Fuel Pump Front Seal + Fuel Pump Top Seal + Side Inspection Plate
* I've never had to deal with this but by the looks of it you'll need to fabricate a locking tool for getting the sprocket off for the front seal, while the belts are still on you may be lucky with a compact impact gun in loosening the big bolt.
For the top seal there's a fair few guides out there if you have a search.
As for the inspection plate, there's a flange with a penny-like indent that's visible from the passenger side of the cab, check the two 10mm bolts aren't loose.
- Water Pump Seal
- Front Lower Case/Oil Pump Case bolts and the missing Weird Bolt
* Myself and another L300 owner called Richie discovered we were both missing a bolt that presides to the bottom left of the water pump and just above the oil pump case, now apparently this is a 65mm deep hole which takes an M8 bolt, however mine nipped up properly with a 55mm bolt - god knows why but it was definitely oily in there.
I actually made my bolt by chopping a longer one down in 5mm increments starting at 65mm, I put some gasket sealant on the washer I used for the bolt just incase, it would seem that there's a nearby oil gully in which the bolt threads into.
Quite odd that it was missing but my feeling is that people may have removed it, lost it when working on the engine, or mixed up the bolts and used it elsewhere. Whatever.
- Any other front engine bolts
* Just go around with your 3/8ths ratchet and 12mm socket and make sure nothing's unusually loose. I found that my water pump bolts were quite slack.
- Power Steering Pump
* Check the bracket bolts here - loosen off the adjustment bolt, remove the PS belt, and pull the pump toward you to gain access to the two bolts that secure it to the block, probably tight but may as well be anal about it, also check the upper bolt and one around the front side of the engine.
- Sump Pan
* The bolts are very small and therefore weak so take caution, there is a paper gasket but instant stuff is also used so that should be scraped off with a plastic tool, cleaned down, and new sealant applied.
- Sump Plug Bolt/Washer
* Ideally, new washers should be used each time but they often get reused, if you are going to be a tight arse then I'd suggest lightly sanding the mating surface then annealing the copper washer with a propane torch till it glows.
- Oil Filter
* Loose fit makes oil sh*t.
- Vac Pump to Sump plastic pipe
* Located on the back of the alternator, oil used to love pooling up on there! If this goes while you're driving it's game over sunshine, so check for possible splits.
- Alternator Oil Feed Unions
* These all take a top and bottom washer for the banjo bolt, in reality they probably won't leak unless loose, get yer spanners out.
- Oil Cooler and Feed/Return Lines
* Located at the front driver's side of the vehicle this if damaged could leak, check the end connections too.
Also if there's corrosion to the lines, oil could from these, replacing these maybe tricky though an option is to chop out the bad bits and then slip a suitable silicone hose on to rejoin, to paint them over with a zinc based corrosion inhibitor paint might be an idea.
First up: finding the actual source of the oil leak. The 4D56 can leak from many, many places, and the area where the oil ends up is not necessarily the source of the leak.
Step 1: Clean your damned engine. Steam clean, degreaser, Q-tips, whatever floats your boat, just get the outside spotless. Not just the oil either, you want to remove all the dirt and dust as that can trap the oil and help transport it away from the source of the leak.
Step 2: Drive it as normal, but after every drive check for oil. If you check often enough, you'll find the source of the oil before it dribbles down the engine.
Another great tip for those tricky leaks is spray foot powder. Clean the engine, then powder the suspect area: the foot powder will show up the oil leaks.
Now, on to the places it leaks, with the most common first:
*** OIL LEAK CHECKLIST ***
THE ENGINE BLOCK
- Rocker Cover Seal + Half Moon Seal + Rocker Cover Bolt Bungs. This is the most common place for oil to leak from.
*Fit a new:
Rocker cover gasket: MD050312
Retrofit an Alloy halfmoon (this permanently cures 90% of all leaks): MD372348 *or* a new original rubber halfmoon (and expect it to leak again in about a year): MD050536
Rocker cover bolt bung MD000523
* Clean up the surfaces with degreaser, then follow the directions in the workshop manual. The rocker cover bolts only need 6Nm of torque so don't go mad. I recommend grey, high-strength silicone, especially for fitting the alloy half moon (which should never need to be removed again).
- Oil Cap Seal
* The seal hardens with age. Sometimes flipping this can cure the leak, you'll need a screwdriver to remove the locking clip. New seal is MD311638, a whole new cap is MN143845
-Side cover by Injection Pump
Gasket: MD020239
Cover: MD020237
Bolts x2: MF140003
Bolt O-rings x2: MD020256
- Dipstick
* If it's loose expect splurting while the engine is running.
*** The Seals ***
* Its a patient job so have plenty of time, obtain some long nose pliers then drill a small hole and then thread a small self-tapping screw in and either pull it towards you or better yet lever it out against something.
You may need to bore a hole on the other side of the original to shimmy the seal out and obviously don't damage the inner surface of the seal mount when drilling as you'll hate yourself for eternity.
If the seal is being an absolute pig you can prize it out either by pulling with a hook and pick tool or with a small flat blade screwdriver and again, something like a bar or handle to lever against - it's okay to rest it on the outer edge of the seal mount.
- Camshaft Seal
* I wedged a breaker bar in between the arms ot the sprocket to loosen, a bit naughty but don't rest the bar on anything that could be damaged easily.
- Upper Balance Shaft Seal
- Lower Balance Shaft Seal
* For the Balance Shafts there is a custom tool pictured in the Tojo T-Belt Guide but no mention of dimensions; so you need a steel bar (Lx450mm,Wx35mm,Dx5mm), bore a hole big enough for your 12mm socket, and then drill 2x 6mm holes 30mm apart each side of the centre hole, you'll then need two M6 x 50mm ->HIGH TENSILE<- fully threaded bolts and nuts.)
- Crankshaft Front Seal
* If you've read the Tojo Guide then you'll understand that in order to get the bottom engine cover off you need to remove the crankshaft pulley! (Slow clap, Mitsubishi...)
There's talk in that guide of using a custom fabricated tool to unlock/lock the crank bolt but to be honest most people use the 'Breaker Bar Method' to get the bolt loose.
Also if the pulley is not budging once the bolt is off then a 6" Jaw Puller will do the trick.
On reassembly, tightening up the bolt is less trivial with the absence of a locking tool -
The best way I've found is the 'Flywheel Jam Method' by wedging a screwdriver or chisel in the centre bottom teeth of the flywheel and securing with lots of cable ties on the bottom subframe bar, but it's tricky as it often slips.
What I tried with success is to use a fat headed stone mason chisel to lock, and then put a trolley jack underneath to apply some pressure to avoid the slip.
Tiny bit of thread lock on the crank pulley bolt, and torque up to a max of 180Nm, job's a good'n!
- Crankshaft Rear Seal
* This requires seperating the gearbox from the engine so most of the time its left alone, I genuinely don't think it would be worth it replacing unless you had a severe leak from there, I definitely didn't do mine!
- Fuel Pump Front Seal + Fuel Pump Top Seal + Side Inspection Plate
* I've never had to deal with this but by the looks of it you'll need to fabricate a locking tool for getting the sprocket off for the front seal, while the belts are still on you may be lucky with a compact impact gun in loosening the big bolt.
For the top seal there's a fair few guides out there if you have a search.
As for the inspection plate, there's a flange with a penny-like indent that's visible from the passenger side of the cab, check the two 10mm bolts aren't loose.
- Water Pump Seal
- Front Lower Case/Oil Pump Case bolts and the missing Weird Bolt
* Myself and another L300 owner called Richie discovered we were both missing a bolt that presides to the bottom left of the water pump and just above the oil pump case, now apparently this is a 65mm deep hole which takes an M8 bolt, however mine nipped up properly with a 55mm bolt - god knows why but it was definitely oily in there.
I actually made my bolt by chopping a longer one down in 5mm increments starting at 65mm, I put some gasket sealant on the washer I used for the bolt just incase, it would seem that there's a nearby oil gully in which the bolt threads into.
Quite odd that it was missing but my feeling is that people may have removed it, lost it when working on the engine, or mixed up the bolts and used it elsewhere. Whatever.
- Any other front engine bolts
* Just go around with your 3/8ths ratchet and 12mm socket and make sure nothing's unusually loose. I found that my water pump bolts were quite slack.
- Power Steering Pump
* Check the bracket bolts here - loosen off the adjustment bolt, remove the PS belt, and pull the pump toward you to gain access to the two bolts that secure it to the block, probably tight but may as well be anal about it, also check the upper bolt and one around the front side of the engine.
- Sump Pan
* The bolts are very small and therefore weak so take caution, there is a paper gasket but instant stuff is also used so that should be scraped off with a plastic tool, cleaned down, and new sealant applied.
- Sump Plug Bolt/Washer
* Ideally, new washers should be used each time but they often get reused, if you are going to be a tight arse then I'd suggest lightly sanding the mating surface then annealing the copper washer with a propane torch till it glows.
- Oil Filter
* Loose fit makes oil sh*t.
- Vac Pump to Sump plastic pipe
* Located on the back of the alternator, oil used to love pooling up on there! If this goes while you're driving it's game over sunshine, so check for possible splits.
- Alternator Oil Feed Unions
* These all take a top and bottom washer for the banjo bolt, in reality they probably won't leak unless loose, get yer spanners out.
- Oil Cooler and Feed/Return Lines
* Located at the front driver's side of the vehicle this if damaged could leak, check the end connections too.
Also if there's corrosion to the lines, oil could from these, replacing these maybe tricky though an option is to chop out the bad bits and then slip a suitable silicone hose on to rejoin, to paint them over with a zinc based corrosion inhibitor paint might be an idea.
