When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a 1970 Cutlass. At some point in the car’s life it received a 403 heart transplant. The engine has the 4B block and it still has the 4A heads.
I’ll admit; before I bought the car, I had some concerns about it having a 403. There isn’t a lot of love for this engine based on what I’ve read online. I must say, however, that I’m very happy with the engine. I’m using the car as a summer daily driver, and in that capacity the 403 works very well.
The engine does, however, consume quite a bit of oil. It uses a quart of oil (10W-40) every 400 miles, which means I’m adding half a quart of oil every 2-3 days.
Early on the engine would misfire every once in awhile. One day it started misfiring constantly above 45mph. I pulled the plugs and this is what they looked like:
It is unknown how many miles were on these plugs. I installed new plugs and the misfiring went away for about 700 miles. At about the 700 mile mark it will misfire a few times over 50 miles or so of driving. I pulled the new plugs when they had 1,000 miles on them, and this is what they looked like:
It’s kind of hard to see from the picture, but plugs #1, 3, 5, 4, and 8 look very good. #2 and #6 are a little bit worse and #7 is in the worst shape after 1,000 miles of driving.
I did a cold compression check on the engine with the following results:
I purchased a 1977 service manual because the 403 was an option in that year, and the service manual indicates those compression readings are acceptable.
I also installed a new PCV valve and that didn’t reduce the oil consumption. The engine doesn’t drip much oil. It dripped a little when I got the car and wasn’t driving it, but the dripping more or less stopped once I started driving the car daily. I was thinking it stopped dripping, but when I came back from a vacation there was a new drip on the floor.
Based on all this information, reviewing the service manual, and doing some research, it looks to me like the excess oil consumption could mostly be attributed to worn valve stem seals or worn valve guides. Do folks try to replace the seals first to see if that helps before pulling the heads and getting the guides repaired? Or would you immediately move forward with getting the guides checked out and repaired as needed?
At this point I’m cleaning the plugs when needed to stop the misfiring. I’d like to address this excess oil consumption issue towards the end of this driving season so I have enough time to get the repair work done and then drive the car enough to make sure the repair work has resolved the issue. Any advice would be appreciated.
Do you notice a large puff of blue/gray smoke when you start it after a hot soak? This usually indicates worn valve guides or bad valve seals. If not you can try a cylinder leak down test. When it comes to oil consumption it basically boils down to worn valve seals or guides or oil rings being stuck to the Pistons. Sometimes you can have a vacuum leak on the underside of the intake manifold that will pull in oil from the crankcase, but it usually will effect the idle quality as well.
As said, start by replacing the valve seals, start on the cylinders with oily plugs. Use compressed air and the little valve spring remover. I use Kleenflo Combustion chamber cleaner sprayed into the cylinders till it stalls, after running it through on fast idle. Then I spray a bunch more and let it sit overnight. It has freed up rings and brought back compression. Your compression numbers are passable for a 7.8 to 1 engine.
7 is definitely wet and maybe 2 and 6? Being that 7 is at the back of the engine on the drivers side I would suspect that maybe the oil return hole is clogged there and possibly filling up enough in the head to surround the valve seal and guide. The rest of the plugs look rich with lots of fluffy stuff that shouldn't be there.
Your compression numbers are excellent so I wouldn't worry about rings or valve face seal.
I'm thinking guides and valve stem seals.
If you still suspect the PCV valve then disconnect it and put in new plugs and drive it for 50-100 miles and see what the plugs look like then. Use it as a breather until the test is done. I don't see the PCV fouling only one plug unless it's specifically tapped into one runner and not the carb base plate.
I've got $10 that says when you pull the valve covers, you'll find that the valve seals are now in pieces in the drainback holes in the head. This is a common failure on Olds motors. The umbrella style seals get hard over time, crack, and fall apart. Naturally, oil consumption goes up dramatically. Worn valve guides will contribute to oil use. I'd consider pulling the heads and having the valves done.
Do you notice a large puff of blue/gray smoke when you start it after a hot soak?
Nope. No smoke out the exhaust, ever. Checked it again today with my son and no smoke at startup, during driving, restarting, etc. I can't recall ever seeing smoke out the exhaust.
Originally Posted by gs72
If not you can try a cylinder leak down test.
I don't have the tool for that, so I haven't been able to try that.
7 is definitely wet and maybe 2 and 6? Being that 7 is at the back of the engine on the drivers side I would suspect that maybe the oil return hole is clogged there and possibly filling up enough in the head to surround the valve seal and guide.
That is definitely an interesting possibility I should look into.
Originally Posted by TripDeuces
The rest of the plugs look rich with lots of fluffy stuff that shouldn't be there.
The engine was running quite rich until I rebuilt the carb earlier this summer.
Originally Posted by TripDeuces
If you still suspect the PCV valve
I didn't actually suspect the PCV valve. I had been searching the forum and I thought that was something I had ran across where someone else had an oil consumption question and the PCV value was something that came up as a suggestion (perhaps more than once). It was something cheap and quick to change so I just did it.
Last edited by Happy Trails; August 11th, 2017 at 02:13 PM.
I've got $10 that says when you pull the valve covers, you'll find that the valve seals are now in pieces in the drainback holes in the head. This is a common failure on Olds motors. The umbrella style seals get hard over time, crack, and fall apart. Naturally, oil consumption goes up dramatically. Worn valve guides will contribute to oil use. I'd consider pulling the heads and having the valves done.
In my driving around today I did manage to stop by the auto parts store. I picked up a set of valve cover gaskets and I'm hoping to make some time this weekend to see what's hiding under the covers.
Your compression numbers are passable for a 7.8 to 1 engine.
I almost forgot to ask you what kind of compression numbers should my engine have? I was in a bit of a hurry when I did my compression test and did it when the engine was cold before heading out on a trip with the car. I thought the numbers were good and didn't think I'd need to do the test again with a warm engine or after adding some oil to the cylinders.
I'm using the 1977 service manual as my reference for the 403 engine, and this is what it has regarding the compression test:
Should I be using a different source as a reference? I only picked the 1977 service manual because the 403 was an option that year, so I didn't put a lot of thought into it.
Last edited by Happy Trails; August 11th, 2017 at 04:55 PM.
I've noticed after taking apart my installation the bottom of the gasket was not fully sealed and was sucking oil through the intake port ruining my fresh valve job. I think the gasket is too thin or the manifold angle is not correct. I will be adding sealant to both sides when I re-install the manifold. I am not aware of a replacement gasket. The non Edelbrock gaskets cover the ports too much.
I've got $10 that says when you pull the valve covers, you'll find that the valve seals are now in pieces in the drainback holes in the head. This is a common failure on Olds motors. The umbrella style seals get hard over time, crack, and fall apart. Naturally, oil consumption goes up dramatically. Worn valve guides will contribute to oil use. I'd consider pulling the heads and having the valves done.
Perfect time to put rebuilt early 350 heads on it, a win win. I have have actually seen the center exhaust seals melted. They still hold up better than the Chebbies of that era.
Last edited by olds 307 and 403; August 11th, 2017 at 05:43 PM.
I almost forgot to ask you what kind of compression numbers should my engine have? I was in a bit of a hurry when I did my compression test and did it when the engine was cold before heading out on a trip with the car. I thought the numbers were good and didn't think I'd need to do the test again with a warm engine or after adding some oil to the cylinders.
I'm using the 1977 service manual as my reference for the 403 engine, and this is what it has regarding the compression test:
Should I be using a different source as a reference? I only picked the 1977 service manual because the 403 was an option that year, so I didn't put a lot of thought into it.
I would say 150 psi would be exceptionally good. I got 140-142 psi on a completely stock 76 350 except with the Performer 204/214 can advanced 2 degrees.
Compression numbers are all close and that's a good thing. These 403's stock were around 8-1 Compression. People that have had a 403 are usually a fan of the engine. You can get a lot of "bang" for the buck and I don't mean bang as in explosion. I agree about the valve seals and maybe the guides are wore but probably serviceable. The problem with pulling the heads is "MAW". If you are going to pull the intake and heads you Might As Well pull the engine and put it on a engine stand. Then you Might As Well get better heads (5,6,7's) and re-ring and bearings, new cam bearings and soft plugs, better camshaft, new lifters, timing set, oil pump, yada, yada. You get the idea, or just put new valve seals and see if it slows down oil consumption. If you do the valve seals, I'd put a step hotter spark plugs. Jmo.
If you still suspect the PCV valve then disconnect it and put in new plugs and drive it for 50-100 miles and see what the plugs look like then. Use it as a breather until the test is done. I don't see the PCV fouling only one plug unless it's specifically tapped into one runner and not the carb base plate.
I just read this paragraph again. I know the PCV valve isn't routed into the carb, but I wasn't sure where it is routed, so I went and took a look. The PCV valve is tapped into the #7 runner, and the #7 plug is the worst. The brake booster is connected to the vacuum source on the carb that would normally be where the PCV valve is connected. This is how it has always been setup since I've had the car.
The car has a Demon carb and a non-stock (unknown specs) cam. I think folks would call it a mild cam. When I setup the carb after the carb rebuild the best vacuum I could get was 12" of Hg.
The Demon carb has one large vacuum source in the rear and two small sources on the side (one for advance and one for diagnostics/accessories). Should I tee into the large line so both the PCV valve and the brake booster share the same source? I think you are suggesting that could fix #7 being the worst, and that makes sense. Would that change affect my brakes? I'm wondering if whoever originally set it up was concerned about the brake functionality.
I replaced the PCV valve shortly after I replaced the spark plugs, so it is relatively new. Should I do anything differently in light of this new information?
You can eliminate the PCV by removing the line and inspecting the inside for oil. If the valve covers have good baffles I doubt its your issue.
I removed the line and used a QTip to swab the line, and there is some oil in the line. Not thickly coated, but some.
I pulled the PCV valve and shined a light in the hole. It kind of looks like the valve covers might not have baffles, in so far as there is no obstruction when I look through the rubber grommet. I can easily see the valves that sit right below and to the sides of the grommet. Surprisingly to me, it looks like the rockers are roller rockers, which I wasn't expecting.
If you still suspect the PCV valve then disconnect it and put in new plugs and drive it for 50-100 miles and see what the plugs look like then. Use it as a breather until the test is done.
I was going to try this today, but the engine wouldn't idle correctly when I tried it. I installed new plugs and disconnected the PCV valve from the hose and I plugged the hose with a bolt. I fired up the car and it idled lower than usual and wasn't steady. I reconnected the PCV valve and it ran just fine.
There are baffled Grommet's out there. Even the factory d shape replacement helped me on my Edelbrock aluminum covers with no baffles. It is smaller on the inside and slightly angled so the oil doesn't shoot straight up. Get either one of these.
Thank you for the links to the parts. The local auto parts store had the baffled grommets, so I bought a set and installed them. I also changed the plugs and started driving the car. I'll know within a few days if adding the baffled grommets helped reduce the oil consumption.
I also purchased a vacuum tee fitting so I can at least try to reroute my brake booster and PCV valve to the back of the carb to further try to prevent the #7 spark plug from fouling so badly.
Thank you to everyone that has helped me so far. It would be incredibly good fortune for me if that $5 part significantly reduced my oil consumption.
The PCV needs to be in the front, brake booster to the rear of the carb. The rubber grommets never worked for me, is there a baffle on the other valve cover?
The PCV needs to be in the front, brake booster to the rear of the carb.
Are you indicating I should reroute the PCV valve hose to the vacuum source indicated by the green arrow below?
Or if I tee them then it should look like this?
Originally Posted by oldcutlass
The rubber grommets never worked for me, is there a baffle on the other valve cover?
No, there was no baffle on the other side.
As luck would have it, there was a set of original looking valve covers in the trunk when I received the car. The baffle covers almost half the valve cover. I'm hoping the grommet baffles work, but seeing how the originals were made makes me wonder.
The car came with a Demon carb. It's an older one before Holley acquired the Demon brand, so it doesn't have a Holley list number. When I rebuilt it this summer I did record all the info so I could figure out which specific carb it was.
It has all the parts for a 750V Speed Demon, with one exception:
- A-12400 primary metering block
- A-12401 secondary metering block
(This is for the mechanical secondary version. The one it should have had would be A-12402)
- Primary jet is 76
- Secondary jet is 83
Other than having a different secondary metering block, it has all the parts for a 750 CFM Speed Demon with vacuum secondary. It has all the parts for the same mechanical secondary model, but this carb has a vacuum secondary.
Tie the brake booster directly into a vacuum fitting in the intake manifold. The factory actually did that on some of the Olds 350's, my 76 Cutlass was that way.
Tie the brake booster directly into a vacuum fitting in the intake manifold. The factory actually did that on some of the Olds 350's, my 76 Cutlass was that way.
I will give that a try before I put too many miles on the new plugs. Rain is forecast for most of the week so that shouldn't be hard to do. Thank you.
I'd be tearing that Demon apart from top to bottom. Notorious pos's. I could write a separate thread on all the problems I found on my three Demons.
For how I'm using the car it's working out so far. I live out in the country and everything is far away and all the paved roads around here are 55mph. Over 95% of my driving is at a steady 55/60mph, so my carb needs are pretty basic.
There doesn't seem to be a lot of love for the 403 or the Demon. Maybe they were meant to be together.
Can't hurt to try the stock valve covers. Seen after market valve covers cause oil consumption to drastically increase. Baffles are usually necessary. My 2 cents.
Tie the brake booster directly into a vacuum fitting in the intake manifold. The factory actually did that on some of the Olds 350's, my 76 Cutlass was that way.
Just a note that I changed the vacuum routing as you suggested and I took the car out for the drive and everything worked well, including the brakes. That change should hopefully help #7.
Can't hurt to try the stock valve covers. Seen after market valve covers cause oil consumption to drastically increase. Baffles are usually necessary. My 2 cents.
I am considering this at some point. If the grommet baffle doesn't reduce the oil consumption I'm going to get another breather and swap out the PCV valve for the breather; basically taking what TripDeuces had suggested one step further with an actual breather. If that is successful then I'll consider using the stock covers. If that isn't successful then it looks like I have deeper issues. I would like to fully bottom out this baffle concern before looking at other areas.
If you do the valve seals, I'd put a step hotter spark plugs. Jmo.
I looked into this a bit. I'm not sure if I can get hotter plugs with this engine. The car came with Autolite 847 plugs. The Autolite website indicates the 847 is the hottest plug for that style of plug. I also bought some AC Delco R46SZ plugs, and that is what I installed yesterday. I found an online forum where someone decoded each character for that plug, and they also indicated 6 is the hottest available from AC Delco.
The RockAuto website only lists those two options for the 403 engine from Autolite and AC Delco, so it doesn't look like I have too many options.
Here's an update now that I have 203 miles since the last time I added oil.
The grommet baffles appear to be helping quite a bit to reduce the oil consumption. Normally I'd need to add 1/2 a quart at this point, but I only had to add 1/4 quart. I should be able to get 800 miles per quart now instead of 400 miles I was getting before.
I pulled the plugs and 6 of them looked more or less brand new. #7 is still the worst, but it had 50 miles of driving where the PCV valve was routed into the #7 runner. #2 is a little darker than the others.
I put AC Delco plugs in this time. This is what the plugs looked like brand new with zero miles:
This is what they look like with 203 miles:
It could be a total fluke, but I also picked up 2mpg with the changes I've made based on everyone's advice. That might not seem like much, but I went from 10mpg to 12 mpg, so that is a huge improvement; unless it was a fluke.
My plan is to get a couple breathers tomorrow and drive the car about 200 miles with two breathers installed and no PCV valve, and see what that does for the oil consumption.
I have a friend that is a good welder/fabricator. Is there any reason I couldn't give him my stock valve covers and these aluminum covers and have him create and weld in baffles that have a similar design to the stock covers?
August 10th, 2017, 05:16 PM
