Could driving an Old Miata hard cause an oil leak?

In April a friend and I did a road trip from Vegas to Maine in a 1990 Miata with 70K original miles. The car was gone over completely, serviced, and some work done, but mostly just new brakes. It had great tires on it. The car ran and drove great. Solid as a rock. BTW, years before, I had a 1994 Miata and a 1993 RX-7, R1 that I soloed.

I drove a lot of winding, hilly miles and put the car through its paces, but never redlined it or abused it AFAIAC. He and I did drive the car 80 quite a bit and during the trip it used less than a full quart of oil. It never smoked noticeably.

Now, six months later it is leaking a quart of oil in about 500 miles. He thinks it is the rear main seal, but hasn’t been specific or taken it to a garage.

This is a car 20 years old that previously spent all its life in Vegas. Now it is in cold Maine. I presume the seals are hard and not doing their job. What might it likely be?

My friend has suggested that my driving the car hard on that trip could have precipitated or caused the oil leak.

I want to help him out if I am at fault.

I can’t think of how driving a car without abusing it would cause a leak. Was he in the car at the time? Did he tell you to back off? Regardless, I can’t think of a reason that your driving caused a leak, especially the rear main seal. It’s an old car, seals leak after a while. Driving like that is why Miatas are built in the first place!

There was a time or two when we hit our first mountainous roads in New Mexico, where I was cornering at 2X the posted curve speed, that he asked me to take it easy and once in a semi-residential area of Austin where he thought I was going to fast for the area. He never suggested that I slow down on the open highway.
He certainly drives more conservatively than I. He typically drove seventy and seventy-five though he did drive it fast and semi-hard on occasion. We intentionally took a Valentine One with us on the trip. He complemented me many times about my ability to drive the car better than he could. He didn’t downshift much to keep the engine in its best power band.

The oil leak is because of the Miata’s age, not the way it’s been driven.

Location means nothing, Vegas or Maine, take your pick; doesn’t matter.

It also doesn’t matter how hard you drove the car. You didn’t hurt it.

You are not at fault, and I have to question your “friendship” with this person. He, or she, is asking WAY too much.

Old car. Old gasket. His oil-changing habits over the years and/or the gasket/rear main seal design work together to determine the longevity of the gasket.

The older oil gets, the more the gaskets take a beating. That is something an owner CAN do to affect the life of gaskets: let oil get old, dirty or laden with pollutants.

I need to clarify that he is a very good friend and hasn’t “asked” for anything. Seeing it from his side, I abused his new toy and may have brought on his oil leak. He has used the phrase that I raped her.
So, whether true or not, he thought I crossed the line a number of times with my driving style. I wanted to get opinions and re-present my case, not just from my view, so he will not blame me and we can put this aside.

As I hear it, the car was well maintained. Supposedly his brother, from whom he bought the car, was pretty religious about maintenance. The only thing his brother did was to hit a rock with the oil pan. The mechanic said it was OK and not leaking before we left. I suppose it is possible that the pan has started leaking. My friend is no dummy about cars, but it has not been up on a lift and he doesn’t know where the oil is coming from for sure. It isn’t obvious.

So first thing is to find the source of the leak - I wonder about the hit a rock thing, there are many ways that could lead to a leak. Has he come up with any idea how just driving could cause a leak?

I don’t think you are at fault and I don’t think you owe your friend anything. Your friend is being unreasonable.

The first thing I would check is the PCV valve. If it was on its last leg, moving it to a cold climate could have made it worse.

The next thing I would check is the valve cover gasket. If it is leaking oil, it is relatively easy and cheap to replace the gasket.

If these two things check out, it might be time for a complete overhaul. A car of this vintage was due to leak oil at some time. Even if you hadn’t taken this trip, your friend would still be having this problem.

If the way you drove it in April had anything to do with it the leak would have started then and there.

It’s 20 years old.

My meticulously maintained '88 Accord started to get leaking seals etc. at ~15 y.o.
I just replaced them at the next timing belt change. It’s normal.

My friend just said:
There is no oil leaking onto the ground! The tale pipe is black, I thought is was rich fuel mixture, but if it is rings; where’s the smoke?
My only other idea is a bad PCV valve, but a new one was put in in Las Vegas (just before we drove it back).

No I don’t think your driving style had any thing to do with the leak but chip in a few bucks to seal her up (this is hardly automotive advice) consider it the cost of the trip.

I hope the cause can be pursued (here-without a new thread), and I can help him out.
I had forgotten about how bad PCVs could pressurize a crankcase. If you have exhaust valve seals leaking couldn’t that be one way to “consume” oil without burning it? Without blue smoke I’m groping for answers. I would thing a quart in 500 miles would not be hard to spot if it were a leak. I think he needs to try the cardboard under the engine, though.
Remember, this car has less than 80K. The only thing this 1990 engine is known for AFAIK is noisy and failing hydraulic lifters. It was a little noisy in that area at low RPMs.

Well, since you have updated the thread and said that the engine isn’t actually leaking the oil, that means that the oil is being consumed by the engine somewhere else.

Things to consider:

PCV system.
Oil control rings on the pistons.
Intake and exhaust valve guides and seals.

Also, has he changed the oil and filter since the trip yet?
If not, he needs to do that first, and it might be worthwhile using a high quality full synthetic oil, as it will resist turning into oil vapor until a higher temperature, unlike conventional oils. Oil vapor gets sucked into the intake via the PCV system, and burned that way.

You’re going to need to perform compression and leak down tests in order to locate the cause of the oil consumption, and devise the best plan of repair.

Overall, you will need to determine the value of your friendship, as he believes that you are the cause of the demise of his car’s engine, and nothing you say is going to change that.

If I were in your shoes, I would buy the car from him, and sell it, and have him buy a different Miata that you haven’t driven. Then don’t drive his cars ever again, as he will always blame you for their issues.


I want to reiterate that we are good friends. He has this link and I would appreciate everyone not disparaging him. We are both 62 and I respect him as an honorable man. I don’t think he really thinks this is my fault, but probably feeling that I should have had more respect and babied his car more. We just drive a lot different. He is a schoolteacher, scraping along and he wasn’t expecting problems with the “new” car so soon. I want to help him figure this out and hopefully it will get resolved without a complete rebuild. I don’t see why a Miata engine, as solid as they are, would be giving up the ghost at less than 80K.This engine was gone over and pronounced sound by a respected Miata mechanic in Reno, referred by the Miata club there, less than 4K ago. It’s got synthetic 10-50 in it.

Wait a minute - 10w-50? Is that the oil specified? 10w sounds ok, but 50? Seems high (thick).

If the car is losing oil, it has to be either burning it or leaking it. There is no other place for the oil to hide.

Sometimes a car can burn oil at a slow enough rate that there is no noticeable smoke, but even with only 80,000 miles, this one could be burning oil, especially if it wasn’t broken-in properly. Remember, service intervals are recommended on a mileage/time basis, whichever comes first. Parts, like seals, belts, and hoses, degrade with time, so a 20 year old car with 40,000 miles could experience the same symptoms if the maintenance was performed on a basis of mileage only.

If you really want to find out why this car is burning or leaking a quart of oil every 500 miles, it is time to let a professional look at it. See if you can find a mechanic with a cylinder inspection tool. It is a fiber-optic tool that you can stick through a spark plug hole to see if the cylinder walls are scoured.

Another possibility is that a part is leaking oil that only leaks when the car is running. If this were the case, there wouldn’t be much oil leaking out while it is parked, and there might not be much of an oil spot where it is normally parked.

10W-50 oil? That could be your problem right there. What kind of oil is required for this vehicle? It should be printed in the owner’s manual, on the dip stick, and/or on the oil filler cap. If your friend has used the wrong viscosity oil, I would switch immediately to the correct oil before more damage is done.

I am willing to bet the correct oil for this car is 10W-30.

I understand about the friendship thing.

I would still recommend the compression and leak down tests, and also the 10W-50 is too heavy an oil for that small, high revving engine. You are robbing horsepower. 10W-40 or 5W-40 is all you should ever need in it.

So here’s what I recommend:

Oil and filter change.
Air filter if it hasn’t been done recently.
PCV valve.
Compression test.
Leak down test.

If there aren’t any external oil leaks, then the oil is going somewhere internally.

Hey, have you checked the coolant?
I would hate to find out that there’s an internal leak that the oil is going into the cooling system under pressure…


Whitey said:
Another possibility is that a part is leaking oil that only leaks when the car is running.

And this can happen when PCV isn’t working.
Oil drips out and gets carried away in the wind.
Make sure the vacuum hose and port to the valve are clear too.