Leaky engine - adding oil without changing oil

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Oct 19, 2022
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What can happen to a leaky engine if I just keep topping up the oil and not actually doing a drain and refill?

The car is a 2000 Mazda Miata with the BP4W iron block, aluminum head 1.8L engine. The engine is not original to the car, which I didn't realize until some time after purchasing the car back in 2019. Compression numbers are excellent, around 200 psi all across. Leakdown numbers are okay, 10-15% across the board. It leaks oil like crazy, but I do not see any visible smoke in the rear view when taking the car to redline.

I used to change the oil once a year since I only drive it about 5,000 miles a year. But the last time I actually did an oil change was August 2021. Since then I've added a full quart of Mobil1 AFE 0w30 SEVEN TIMES now, in less than 7K miles. Filter issues aside (I know I need to change the filter), what can happen if I don't fully drain the oil and replace with the usual 4 quart capacity? Seeing as how I've added 7 quarts, those 4 quarts I put in 15 months ago is pretty much gone for all intents and purposes.

I do have plans to pull the drivetrain out this winter, and re-seal the entire engine. Front to back, top to bottom. Both crank seals, flywheel bolt sealant, oil pan lip seals, new oil pan sealant, camshaft seals, cam cover gasket, oil cooler o-ring, and anything else I can find associated with sealing the oil inside the engine. After that I will obviously go back to regular oil changes. And given that I'll be draining the oil in the next couple of months before pulling the engine, I don't see any point in changing the oil now, only to drain it yet again at that time.

I will also take a sample of the oil that comes out and get a UOA of that oil, while I have the engine and drivetrain all apart.

The car has about 172K miles on it, but unfortunately I have no idea how many miles are on the engine, or if it's ever been rebuilt.
 
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A couple of previous threads on this topic:

 
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What can happen to a leaky engine if I just keep topping up the oil and not actually doing a drain and refill? ...
I've added a full quart of Mobil1 AFE 0w30 SEVEN TIMES now, in less than 7K miles. Filter issues aside (I know I need to change the filter), what can happen if I don't fully drain the oil and replace with the usual 4 quart capacity? ...
One issue that comes to mind is insolubles (carbon, metal, debris) or sludge building up in the bottom of the pan. They'd flow out with the oil if you drained it.
... It leaks oil like crazy, but I do not see any visible smoke in the rear view when taking the car to redline. ...
1 quart every 1000 miles is a lot. If it's leaking that bad, maybe it's been overheated? It may be combination of leaking & burning. A full throttle run to redline checks ring seal. How about valve guides - if it sits for a few days, does it blow smoke on the first cold start?
 
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So if it leaks…. Different than consumes oil. But if it leaks use high mileage oil.
 

PatrickGSR94

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Buy a new vehicle.
HAH! I'd love to get rid of this car and get a NC Miata instead. But no way I could afford one right now. Plus, I'm the type of person who tinkers with and tries to fix stuff before selling it.
One issue that comes to mind is insolubles (carbon, metal, debris) or sludge building up in the bottom of the pan. They'd flow out with the oil if you drained it.

1 quart every 1000 miles is a lot. If it's leaking that bad, maybe it's been overheated? It may be combination of leaking & burning. A full throttle run to redline checks ring seal. How about valve guides - if it sits for a few days, does it blow smoke on the first cold start?
I have not noticed any smoke blowing out, either on cold start or when doing redline runs up highway on-ramps.

I can only assume that the car's original engine was overheated and then replaced with this one. The car was obviously autocrossed previously (came with AutoX class-legal mods like brake lines and aluminum radiator, and huge front sway bar). 90-05 Miatas are known to have cooling issues under track use, being that the engine was originally designed for a FWD application. Some people do coolant reroutes to remedy the situation, but the consensus is that it's not really needed for street cars. Couple that with the fact that the dash coolant temp gauge is utterly useless, and you get a recipe for overheating that's all too common.
 
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PatrickGSR94

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A couple of previous threads on this topic:


thanks for the links. I tried searching but didn't use the right terms I guess.

Since continual topping-up is not a long-term solution I'm not that worried about it. I'll pull the engine out, seal it up, and then see how it goes.

I've had 3 UOA's done on the car before, the last one with 2 quarts added in 5K miles, and the one before that with 1 quart added in 4K miles. Although I'm not sure I kept accurate records of every time I added oil. Now I'm at 7K with 7 quarts added, but I've also kept better records so I know for sure that's the actual amount. But on all those reports, all the wear metals looked fine, with some even declining from previous reports.
 
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What can happen to a leaky engine if I just keep topping up the oil and not actually doing a drain and refill?

The car is a 2000 Mazda Miata with the BP4W iron block, aluminum head 1.8L engine. The engine is not original to the car, which I didn't realize until some time after purchasing the car back in 2019. Compression numbers are excellent, around 200 psi all across. Leakdown numbers are okay, 10-15% across the board. It leaks oil like crazy, but I do not see any visible smoke in the rear view when taking the car to redline.

I used to change the oil once a year since I only drive it about 5,000 miles a year. But the last time I actually did an oil change was August 2021. Since then I've added a full quart of Mobil1 AFE 0w30 SEVEN TIMES now, in less than 7K miles. Filter issues aside (I know I need to change the filter), what can happen if I don't fully drain the oil and replace with the usual 4 quart capacity? Seeing as how I've added 7 quarts, those 4 quarts I put in 15 months ago is pretty much gone for all intents and purposes.

I do have plans to pull the drivetrain out this winter, and re-seal the entire engine. Front to back, top to bottom. Both crank seals, flywheel bolt sealant, oil pan lip seals, new oil pan sealant, camshaft seals, cam cover gasket, oil cooler o-ring, and anything else I can find associated with sealing the oil inside the engine. After that I will obviously go back to regular oil changes. And given that I'll be draining the oil in the next couple of months before pulling the engine, I don't see any point in changing the oil now, only to drain it yet again at that time.

I will also take a sample of the oil that comes out and get a UOA of that oil, while I have the engine and drivetrain all apart.

The car has about 172K miles on it, but unfortunately I have no idea how many miles are on the engine, or if it's ever been rebuilt.
Keep adding oil and when you get the money retrofit 1 of those LS1 engines , get yourself a LS3 crate engine, take off the heads that are not really good for the street, then again your car is light, so cathedral port AFR heads might spin to much tire down low so the rectangle port heads should be fine.

Great car, do not get rid of it
 

PatrickGSR94

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lol not really interested in high HP cars to be honest. I'm more into the "slow car fast" kinda thing. One can have plenty of fun and get into plenty of trouble even with the stock 140hp.
 

wlk

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Leaking? Do you have puddles under the car? Or is it just burning while driving? If the later maybe the rings are stuck and a run or 2 of HPL EC40 may do it some good. Is the PCV system clogged?
Puddles try the EC40 and maybe some liqui moly motor oil saver afterwards may do it some good.
Maybe you have tried these but just a thought
 
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I do have plans to pull the drivetrain out this winter, and re-seal the entire engine. Front to back, top to bottom. Both crank seals, flywheel bolt sealant, oil pan lip seals, new oil pan sealant, camshaft seals, cam cover gasket, oil cooler o-ring, and anything else I can find associated with sealing the oil inside the engine.


Seems like a lot of work. I would try to track down specific areas that are leaking and fix those.
 
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Do you have puddles under the car? Or is it just burning while driving?
It leaks oil like crazy
^ This. Is it leaking on the floor or is the engine consuming the oil?

If it is actually leaking and dripping, you'll have huge puddles in the parking spot and the undercarriage will likely be coated with oil. The solution here is obviously to fix the leak.

If the car is consuming the oil, that's a different problem altogether. You may not see any visible smoke even when the car burns oil at this rate. With this mileage, most Mazda engines will have significant blow by and burn some oil. My 2.5L Mazda V6 in the Probe GT had 140K and burned oil at a similar rate to yours. I switched to high-mileage oil and it made a huge difference, I'd say it reduced the burning rate by ~75%.
 
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i am loosing 1 qt every500 miles in my sorento due to valve cover gaskets leaking. its a uber difficult and long difficult job on the 3.5 v6. sigma oil stays pretty clean for a long time. i just did a oil change at 5k and the oil looked like it could have gone another 2-3k easy
 
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