Losing oil... time for heavier weight?

[JJorgensen52]

I switched my '69 307 to Mobil1 synthetic, 10w30, the last time I changed the oil. (Not here to discuss the use of synthetics, I have my reasons and will be sticking with the Mobil1).

that said, the truck has been loosing a lot of oil, almost exclusively during highway driving. Like, about a quart for every 125 miles. It's got no trace of leaks and it isn't smoking like I would expect.

So my question is, assuming I have worn valve seals (compression is even at least, seems fine but will be checking it next weekend), will going to a heavier oil help reduce the rate of oil consumption? What weight do you normally run?

I'm looking at either a 10W-40 or 15W-50 at this point.

[cdowns]

changing your oil will accomplish nothing

[JJorgensen52]

Originally Posted by cdowns

changing your oil will accomplish nothing

Thanks for the ultimatum

What leads you to say that? I'm not new to engines; I know that using and oil that's too thin can cause problems, such as low pressure, leaky valve seals/guides, noisy lifters, piston ring bypass, etc.

The research I did earlier today indicates that these trucks came with a heavier weight oil in them than the 10W30; additionally, the synthetic oil is slightly thinner than conventional oil.

I am in no way trying to ignore the fact that I'm loosing oil from the truck. I am simply looking for a little bit of a band-aid fix to slow (stopping would be awesome, but I am not that optimistic) the oil consumption down until I take the truck off the road at the end of the winter. I have a tear-down and rebuild in mind for this motor in the next 6 - 8 months

[68gmsee]

You can try the heavier weights, but I think what CDowns is saying is that if you're burning 1 quart every 125 miles changing from 10w30 to 10w40 or 50 is not going to keep the consumption down that much.

Intresting that you see no smoke when you first crank it up. That's a sure sign of bad valve guides. But, if the compression test shows good compression and engine is not smoking while you're going down the road (best noticed by an observer behind you) then your hunch is correct -head rework will help.

[cableguy0]

I'm gonna assume switching to synthetic on the old motor has cleaned things up a bit and removed buildup which was stopping the oil from burning before. You wont hurt anything by trying the heavier oil and in an older engine its usually not a bad idea anyways. I would start with 15w40 but dont set your expectations too high. Theres a good chance it wont help much. Switching to synthetic on such an old engine probably wasnt the best idea. I use nothing but synthetic but it usually causes issues with oil burning or leaks in old engines like your experiencing because it cleans everything so well.

[msgross]

my old S-10 like rotella and nothing else... 10W-30 and she would start burning it slowly..

[JJorgensen52]

Originally Posted by cableguy0

I'm gonna assume switching to synthetic on the old motor has cleaned things up a bit and removed buildup which was stopping the oil from burning before. You wont hurt anything by trying the heavier oil and in an older engine its usually not a bad idea anyways. I would start with 15w40 but dont set your expectations too high. Theres a good chance it wont help much. Switching to synthetic on such an old engine probably wasnt the best idea. I use nothing but synthetic but it usually causes issues with oil burning or leaks in old engines like your experiencing because it cleans everything so well.

I had thought of the potential for cleaning and leaking, too; when I did valve cover gaskets everything looked pretty clean (and being a sub 70k engine) I figured it might not hurt me to give it a shot.

I suspect the lack of smoke may partly be due to how blasted cold it is here, as the truck is always steaming when it's warming up anyway. Might be enough to cover up the oil smoke from the seals, but with the rate of consumption I would have expected a LOT of smoke.

As a side note to that, does anyone know if synthetics smoke less?

[463]

what i would do is change back to the oil that was in use before the switch to Mobil1 synthetic. and see what happens. with a sound engine making the switch to synthetic has a cleaning efect and not much more. on older units it will find it's way out (leak), consumption on the highway is more or less the same. with stop and go driving just a bit higher. i like to check the oil cold before i run the auto and keep tabs on it till i understand how my drive style relates to the oil use in the engine and then go from there as to whether it's a oil user or not.

[JJorgensen52]

Originally Posted by 463

what i would do is change back to the oil that was in use before the switch to Mobil1 synthetic. and see what happens. with a sound engine making the switch to synthetic has a cleaning efect and not much more. on older units it will find it's way out (leak), consumption on the highway is more or less the same.

This presents a slight problem - the engine had a hodgepodge of oil in it before this. I found 3 different brands / ratings / weights of oil (empties) in the fenders when I was cleaning it up after first buying it. The PO was a mechanic of some fashion and it seems like he just used whatever was laying around the shop on the truck. Parts missing, custom brackets, parts from cars/other makes, you name it.

I am planning at this point to try a heavier weight synthetic and see what the result is; failing there, I'm going to just start feeding it conventional oil and hope that helps (or if not, at least regular oil won't hurt my wallet as much until I can rebuild the motor)

[cableguy0]

I dont know for sure with mobil 1 but i know royal purple does not smoke. Royal Purple gets used in a ton of cars that go to auction for that very reason.

[Ticker]

If you're really confident that the only thing that's changed is the oil, then I suspect - as noted by others - that the comment below from the Royal Purple website is what's happening:

"Properly formulated synthetic oils will generally not cause an engine oil leak. Synthetic oils possess a higher degree of natural solvency, which can clean and remove deposits left by previous oils. The removal of extensive oil deposits can expose marginal or damaged oil seals, which may then leak. If an engine currently has excessive oil consumption (i.e. greater than 1 quart / 1,000 miles) the recommended course of action is to solve the oil consumption problem before switching to a synthetic."

FWIW, by running a synthetic without sufficient ZDDP for your flat tappet cam you'll be doing an overhaul here pretty quick. Not trying to "discuss your reasons" - just telling you what *will* happen.

[JJorgensen52]

Originally Posted by Ticker

FWIW, by running a synthetic without sufficient ZDDP for your flat tappet cam you'll be doing an overhaul here pretty quick. Not trying to "discuss your reasons" - just telling you what *will* happen.

According to what information I can find on this subject, the original flat tappet additive level was .08% phosphorus from ZDDP, approximately, when it was introduced. Higher levels were later used for high spring pressure / high lift applications (not my 307).

Mobil1 contains the same .08% phosphorus as the older oils. The heavier oil, 15w50, contains 0.12%. This is much closer to the levels used in more powerful engines in the 60's.

Perhaps not the most conclusive, but it will do for me.

As an additional note, I am running my Typhoon (4.3l v6, flat tappet Comp Cam, 492hp turbo) with Mobil1 10W30 as well. That is the ONLY oil recommended by GM at the time of manufacture, as well as the builder I worked with when building the current motor. In this motor, I spun two cam bearings because of a faulty lifter which exploded and dropped my oil pressure to <5psi at 6000rpm. When that cam came out, other than having two spun bearings, it didn't have a single heat or wear mark on it after 4000 miles. One of the reasons I prefer to run synthetics.

[Ticker]

Originally Posted by JJorgensen52

According to what information I can find on this subject, the original flat tappet additive level was .08% phosphorus from ZDDP, approximately, when it was introduced.

The API and ILSAC specifications are the *only* data that matters.

See the "Flat-Tappet Oils" link in my signature for the correct and complete answer. But, as noted - it's your truck

[BluTrukker]

My daily driver is a 92 toyota paseo (don't laugh it pushes 40 mpg) It has a 1.5 and the first engine I had in it just plain wore out(250,000miles). It still ran good, but the cylinders were worn beyond the high limit specs. Needless to say it burned about a quart every 150 miles or so. I started adding 1/2 qt of Lucas Oil additive when I changed oil. It significantly decreased the amount of oil I was using, and put a bandaid on the issue until I could get another engine lined up. So that is my recommendation for a temporary fix.