Oil Consumption 1965 mustang 289

A few years ago I purchased a 65 Shelby clone. It runs fantastic, lots of power. The problem is that I am adding oil to it regularly. There are times when it does smoke a little at start up, especially after it sits for a long time, but it seems the more that I drive it, the less frequent this happens. When I drive it, I have not noticed it smoking. I know the car sat up for the last several years and was driven rarely (purchased it from a friend). The engine has very good oil pressure and is really quite strong. The engine has had some modifications, but nothing drastic. How do I know if I need a rebuild and if I do, how much should I expect to pay.I will tell you that I have driven the car on 150 mile trips to shows without any issues (except oil consumption). Are some cars just due to use oil?  

What kind of valve stem oil seals are You using on that motor? The original umbrella style seals sometimes allow too much oil to get past the valve stem and down the valve guide into the combustion chamber to be burned off.

I had a nice rebuilt motor with umbrellas that did the same thing as yours. I took the heads back and had them install circular valve stem seals and never used a drop of oil betwwen changes again after that. Worth a look.

Since your motor has good power, doesn't smoke and oil pressure is high I'd look there. Also make sure your PCV (if you have one) is working properly and not sucking oil vapor. On the surface it doesn't sound like you need a rebuild.

What do your spark plugs look like?

Have you done a compression test?

How many miles on the motor since it was rebuilt or new?  

Not sure of the valve stems. I had the compression checked and it was good. I just put in new plugs. The old ones looked clean (for old plugs). My PVC looks a bit oily. I need to change it. Not sure of the mileage. I would suspect that it is not very high since the car was restored several years ago, but not driven much. How expensive is it to check the oil seals? Do you think that is my issue? My oil pressure when warm is about 65-70 lbs at about 3500 rpms?  

Your oil pressure sounds really good. If it blue smoked a lot, especially under load, I'd question your piston rings... but everything sounds good including compression that almost eliminates that issue. Things seem to point to the seals.

You can just remove a valve cover and look at the valve stem with a flashlight where it comes out of top of the cylinder head inside the valve spring beneath your rocker arm. If it is kind of an umbrella or mushroom looking thing then you have umbrella seals. If it looks like a small plastic donut with the valve stem running through the middle of it then you have circular style. My bet is you have umbrella style seals that are stock replacements. If so, you could remove the heads and have a reputable auto machine shop do some minor machine work to accomodate and instal good circular seals. It isn't that expensive, especially compared to an engine rebuild. If you did an engine rebuild you'd have to do this anyway. So why not do this easy part first and see if that cures your problem?

While the heads are off you can check the valves themselves and the valve guides to be sure they are OK too. Still cheap. Too much clearance beween valve stem and valve guide lets too much oil pass. Some builders prefer to use bronze vs cast iron valve guides because bronze is more porous and holds more oil. If you have the heads inspected and all necessary work done and put back on the motor and it still smokes then about the only thing left is to have the cylinders cleaned up and new rings installed or do a complete short block rebuild which can get into some money. At that point you will already have the top half of the motor done and know the rings are the only thing left that could be causing it to smoke by a process of elimination.

Usually smoke out the back of the tailpipe is caused by bad rings, bad valve seals and/or bad valve guides that don't control oil. Sometimes a bad PCV valve will suck oil vapor or raw oil into the motor, especially if the baffles in the valve cover are missing. From what you describe it sounds like valve seals. The plugs might look worse if it was something else and it would smoke more.
I think you can fix it without too much of a problem.

How much oil does the engine use? What type of oil do you use?
Have you ever worked on engines?(trying to determine your experience level).  

I recently drove to a show (interstate) which was about 140 miles round trip and used about 2/3 quart of oil. I use 10w 30 Castrol GTX. I have done very little engine work. I did replace the lifters, but had someone supervise me to make sure I did it correctly. I would have to take it to a shop to have this work done.  

Yeah, 2/3 of a quart in 140 miles is way too much. Barring any external drips or leaks that would be visible on an exterior engine inspection or on your garage floor to indicate oil loss sources other than being burned I'd say you should first pull your cylinder heads and take 'em to a good auto machine shop for inspection and new circular seals. If you need new valve guides I'd go with bronze, otherwise leave what you have if they check out OK.
 
I say this based on the fact you said you don't see smoke coming out of the car except for when you first start it and that the spark plugs look clean and engine compression was good on a fairly new motor.

It seems some oil is getting into the combustion chamber and being burned. The valve seals and guides would be the first place I'd look after being sure the PCV system is working properly.

The friend that helped you put new lifters in might be able to help you pull the heads too. Its not that hard to remove and replace if you know what you are doing or have done it before. You would be looking at a weekend or less to remove them and another to put 'em back on once the machine shop is done. That would save you much money in labor. The actual machine shop costs would not be bad for the light machine work and new seals. Even new guides don't cost that much if you need them, which you may not. Then you will have many miles of enjoyment with an engine that doesn't use any or much oil between changes.

If you decide to pull the heads yourself and need help.. come back on line. I've done cylinder heads many times as I'm sure so many of the other folks on this site have and would be glad to offer you tips to make your job much easier.  

How much modifdfying has been done? It kinda sounds like the vaulve seats might be either bad or going bad. that or your intak manifold gasket is leaking or a head gasket.  Mine smoked untill I resealed the intake manifold and oil pan. The oil consumption could actually be a leak somewhere. Have you noticed any drips on your garage floor? It could also be the wrong type of oil. If it is too thin it could be getting past the rings and vaulves. It could, like you said, just be time for a rebuild.  

There is some very minor visible oil around the oil pan (over sized pan), but no real leaks on the garage floor. If the PCV valve is not functioning properly could that be the reason? Would you advisee using a heavier weight oil or treatment?  

What kind of expense would I be looking at if I did have to pay someone to rebuild?  

Really be sure you don't have any oil seepage coming out of the motor anywhere. It doesn't take much to loose 2/3 of a quart one drip at a time. Take a flashlight and really look the motor over including the rear main seal area where the lower bellhousing bolts up to the back of the block. It would be a shame to spend alot of money rebuilding only to find out you had a tiny leak somewhere causing the problem.

You are using 10-30W oil right now which is OK in a cold/mild climate. Not sure where you live but I would either go to straight 30W or 10-40W if you drive the car mainly in the spring/summer to shows. Especially go to the higher grade if you live in a temperate climate. That might slow down the consumption rate a ***

If your PCV and associated hoses and baffling aren't working properly it could cause the motor to injest oil and/or oil vapor that would tend to deplete your oil over time. Some aftermarket valve covers don't have the baffles inside the valve cover to help prevent this from happening or the baffles were removed by a previous owner. Really be sure your PCV system is set up right. The oil filler cap needs to be a solid type and not vented or oil could be forced out of the vented cap. PCV systems were designed to use the solid cap and a hose going to the air cleaner to drawn in filtered air to the crankcase to pick up pollutant vapor and then up throught the PCV valve into the carb to be burned off in the combustion chambers. If it isn't set up right it could pick-ip oil as well.

If you pull the original motor and have a good machine shop rebuild it for you it could be up to several thousand to really do it right. If you don't care about keeping the original engine in the car, etc. you could buy a crate motor for less and install that. The labor to pull and reinstall the motor if you don't want to do it yourself would be an additional amount at current shop rates but guessing another $500-$800 or more in labor to R&R.
That is why I mentioned it might be wise to have a good shop inspect your car for oil leaks and do a PCV sytem check to be sure all that is OK first before tearing into the engine. If all that checks out you are down to the valve seals/guides and piston rings as the culprit. Since you have good compression I'd say it would be a good bet at that point to just do the heads since two of your 3 potential remaining trouble spots are there. Removing the heads is easier and cheaper than removing the entire motor by a long shot. To fix the heads may only cost a couple hundred $ for the machine work and seals/guides. The labor to have the heads removed and replaced would be much less too. If you do decide to rebuild the block later on then you could deduct the price of rebuilding the heads from the earlier mentioned price to rebuild the entire motor since that would already be done.
So get an oil leak inspection and PVC inspection and change to heavier grade oil to start. If you still have trouble then yank the heads. I think you will be fine at that point with minimum outlay of cash and you will know for sure what was wrong before spending big bucks on an engine rebuild when one might not be necessary yet.  

Thanks for the advice. You have been very helpful. I think I will take it one step at a time. Check for leaks, PCV valve, proper oil weight. My mechanic told me that this motor is a strong performance motor and may use some oil. Again, thanks for your advice. This is a great blog!  

I think going slow on this is a good choice. A few quarts of oil here and there in an otherwise strong motor is a much cheaper alternative than a costly tear down.
Good luck with everything.  

Hi eagles 1 and others,
I pretty much agree with most of the conversations here but want to point out that just because you have good compression doesn't rule out oil getting past the oil control rings on the pistons. It just means the upper rings are still sealing. IMO 2/3 of a qt in 140 Miles is a pretty heathly oil burn. I would expect worn out valve guides and umbrella seals being the the most likely cause of the oil usage. You can go to a single weight oil, I suggest 30W, and see if it gets better. If you want to see the overall condition of your rings, plug the PCV valve and look for the smoke that comes out of the breather cap (its called blow-by)if there's a lot of blow by, you have ring issues.
jlg