Greetings all! I have owned my 1985 Oldsmobile Delta 88 with 307 V8 since April of 1985. Through 106,000 miles, I have had to have the intake manifold gasket replaced five times at 15,000 to 20,000 mile intervals where the gasket fails at coolant passages. In frustration, I decided to replace the factory aluminum intake with cast iron as one of the Oldsmobile dealers who changed one of the gaskets indicated this would be a long-term solution. The only cast iron manifolds that I have found are large port and the heads on my car’s 307 V8 are small port. Am I foolhardy to consider using one of these cast iron manifolds despite the mismatch — or should I go back with the original Aluminum and hope to get at least 20,000 miles before the gasket fails again.

 

What gasket are you using that is failing ? The factory style "turkey tray" ?? I think the mismatch on the cast manifold would be terrible. I dont know about the factory Olds aluminum intakes but there are literally millions of cars running around with aluminum intakes and no issues. I don't know who you are having replace the gaskets each time but I would look for a shop that is familiar with older cars and performance.

 

There has to be an issue. Maybe the intake is warped. These only fail occasionally, not every 15,000 Miles. Did they use RTV when installing?

 

Bad ground, is the surface pitted due to a stray current? Using proper coolant?

 

I had an 85 442 that would do the same thing just about every 15 to 20 thousand miles. Nothing would stop it, Cadillac radiator pellets, positive ground to block, distilled water mix, nothing... I replaced the A4 intake with a cast iron number 16 and the problem went away. If your intake is an A5 the ports will not match up, only if yours is an A4 will they match.

 

My original selling dealer has handled all but the first replacement and the current. I have trusted their service department for over 40 years of trouble free motoring with this one exception. The last replacement was handled by one of their mechanics with 30 plus years of experience as a GM Service Technician. They have assured me multiple times that there isn’t anything wrong with the intake manifold or the heads. The mechanic and service advisor suggested considering switching to the cast iron intake after the last failure. I just didn’t realize that there was a difference in heads on the 307 from one model year to the next so was relieved when I found a cast iron manifold from a 1984 307, bit after having it shipped to my mechanic we discovered the port size differences.

 

All of the replacement gasket sets have been those recommended by GM — the metal tray type with composite seals on either end. My original selling dealer has performed all service on this car including replacing the gaskets except the first that failed while I was visiting three states from home and the current install. My current mechanic is taking every precaution to insure that the job is done correctly, and I have extreme confidence in the quality of his work. I purchased the 1984 307 cast iron intake before either of us realized that there was a difference in port sizes, and every available intake that I have found since learning about the small port heads has been aluminum so it looks like we may be forced to reuse the original aluminum intake and hope that it will remain sealed as long as I am able to drive as I am getting along in years.

 

I am not certain about the earlier replacements using RTV, but am sure that it was used if recommended by GM as the repairs were handled by reputable Oldsmobile dealer’s service centers. The most recent replacement had a very light film of RTV. I have been assured multiple times that the manifold isn’t warped and that the heads are true.

 

Ground is one issue that hasn’t been addressed to my knowledge. I have never experienced any kind of electrical problems with this car, in fact, the original alternator didn’t fail until it was 30 years old and had 99,000 miles. The Antifreeze is that which is recommended by GM and has been flushed at the end of every fifth season,

 

My original intake is a A5 with 7A heads. It is beginning to look like the only intakes for those heads are the aluminum as I haven’t found any cast iron compatible with the 7A heads at any of the many salvage yards that I have contacted.

 

Yes, only aluminum intakes with the 7A heads. I am surprised this issue is this bad on some of these cars. We had a few come in for service and one for sale at the shop I apprenticed at, never for intake gaskets. All the early 307 big cars, quite a few came through the shop, up here, all had #17 iron intakes. I had to get an A4 from the US for my Olds powered truck, as only the H/O and 442 had them in Canada, from what I saw. The #17 intake should bolt on and seal. Some have used the Performer on 7A headed 307's, so it must be possible. Tell them to try an early intake gasket dry, if it is completely covered by the head mating surface, it will seal. Is this ideal, no. Is pulling an intake every 15,000 miles ideal?

 

Tell them to trash the end seals and use a bead of RTV instead. A lot of times the end seals will be too thick and not allow the ends of the intake to pull down all the way. Its rare for that to happen on an unmolested engine but you never know. I never use the end seals on any engine unless it is a restoration and has to look original.

 

The only aftermarket intake that’ll work properly on the small port heads is the old Edelbrock SP2P.

they come up for sale on here once in a while

 

7A heads are not small port heads. They are the same as any small block head.

 

He is not talking about 72 Olds 350 7a heads. It is the later smaller, 307 swirl port 7A heads.

 

I'm just curious, how exactly are the gaskets "failing" ?

 

Sorry I did not know there was two different 7A heads. I had a set of 350 heads from a 72 that were 7A (large A) heads.

 

A 1986 Olds 307 from a Buick wagon was the first Olds V8, I pulled apart, tiny ports. I was an apprentice at a Ford dealer in 1997. The owners ex Wife blew it up, myself and the other apprentice pulled it down. I believe a rod went through the block. I kept the 80 cfm Qjet which actually came off a 80 Pontiac, when I decoded it a while back. I was driving a 81 Delta 4 door at that time, what a great car that was.