Intake manifold oil leaks

[Michael Jones]

I have the 2x4 aluminum intake manifold and I have to constantly dab oil from around many of the bolts holding the manifold to the heads. Since I'm going to be removing the manifold to detail the engine, is there anything that can be donme to eliminate the oil that slowly oozes up around these bolts?

Thx,

Mike

[Joe L.]

Re: Intake manifold oil leaks

Michael------

Yes, there is. Try this:

1) THOROUGHLY clean all intake manifold bolt thread holes. This can be a difficult, time consuming job with the heads mounted on the engine, but it must be done THOROUGLY and COMPLETELY so that the threads are 100% clean of oil, grime, etc. I recommend using repeated applications of brake cleaning solvent

2) THOROUGHLY clean all intake manifold bolts so that they are free of oil, grease and grime and are as clean as new bolts. Use the brake cleaning solvent for this, too

3) Apply Permatex non-hardening sealer to the bolt threads, insert the bolts and torque to specification following the sequence and procedure found in the Chevrolet Chassis Service or Overhaul Manuals.

The bolts that are critically important to solve the oil seepage problem are those that go through to the intake valley. However, I usually treat all the bolt holes the same.

[Joe C.]

Re: Intake manifold oil leaks

Michael:

I agree fully with Joe ("cleanliness is next to Godliness").Another excellent product I have used with great success is GM "Pipe Sealant With Teflon", available from your friendly GM dealer. It is fairly expensive, and there are similar thread sealants with teflon avail. at auto parts stores for less.

I believe that the teflon is a good lube, which will give a better and more consistent torque reading when you "make up" the bolts.

Joe

[Craig S.]

Re: Intake manifold oil leaks

You are right, and I think the ACE Hardware Teflon paste sealant works equally well and is far cheaper than the tube I have from ARP.....Craig

[Joe L.]

Re: Intake manifold oil leaks

Joe-----

Yes, I like that product, too. I use it in many applications. It's actually a Permatex/Locktite product and it's available under their brand name as well as GM. However, wherever you get it, it's still not cheap. I think this product is actually supposed to be a sealer and low-strength thread locking compound in one, and that's the reason for its price.

One other thing, though, is this: the bolts that are always the most troublesome with respect to oil creepage are the two centermost bolts on either side. These are also the same ones exposed to very high heat since they "straddle" the heat crossover passage. I'm not sure that any generally available automotive sealant is up to the task of withstanding the heat involved for any considerable period of time. So, although I've never actually tried it, I think that the use of Teflon pipe sealing tape might be best for these particular 4 bolts. The Teflon tape should be capable of indefinitely handling the high heat without breaking down. And, the Teflon tape seals very well for pipe joints.

Like I say, though, I've never tried it. But, in principle, it sounds to me like it might be the way to go.

[John H.]

Re: Intake manifold oil leaks

Due to the large number of ARP bolts I've used on other project cars, I keep their "Thread Sealer" and "Assembly Lubricant" on hand as well, as that's what they recommend. I've used the ARP "Thread Sealer" exclusively on both head bolts and intake bolts on many engines over the years, and have never had a leak of any kind - I can't stand leaks either. The four corner intake bolts are blind-tapped; all the others are open to the hot oil vapors in the lifter valley. Without a good quality thread sealer on those other bolts, oil will eventually migrate up the threads and appear as oil stains around the bolt heads.

[Steve D.]

Re: Intake manifold oil leaks

What is ARP ?

[John H.]

Re: Intake manifold oil leaks

Steve -

ARP stands for Automotive Racing Products, the premier manufacturer of top-grade aftermarket fasteners for stressed applications - the best in the business, bar none ( www.arp-bolts.com ). I use their products exclusively for main studs, rod bolts, head bolts, rocker studs, and many chassis applications.

[Allan Hein]

Re: Intake manifold oil leaks

Can one succcessfully seal two bolts by the recommended cleaning and teflon sealant method without causing more problems with the other bolts or uneven stress/torque? The intake manifold depression nearest the carb front passenger's side on my '66 425 HP requires the occasional removal of a small amount of oil.

[Clem Z.]

Re: Intake manifold oil leaks

any time you a deposit on the intake manifold and you think it is oil,taste it as it may be gasoline that came from the carb and as the light ends evaporate from the manifold heat it may look thick like engine oil.

[mike hom]

Clem is right. How do you stop it?

I have a similar problem with my 65 (396/425). I have to regularly swab up small amounts of gasoline from the intake manifold on my car. Before I realized that this was a fact of life, I would not think to check this for a couple of months, and after being exposed to manifold heat this effluent did look like oil. It is, however gas, at least in my case.

I seem to recall someone on "Da Board" referring to this as "Holleyitis". Does anyone know what causes this and is there a remedy?

[Clem Z.]

Re: Clem is right. How do you stop it?

if the leaks are not external,the gaskets or the accelerator pump,the problem is the fuel boiling in the float bowls,coming out the boost nozzles,dripping on the butterflys and then coming out past the throttle shafts onto the manifold. try lowering the floats. blocking the heatriser cross over on aluminum manifolds is the best answer. a insulator spacer under the carb MAY help. i always turn a holley carb upside down and pressurize the needle and seats to 10# with a hand pump to see if they hold without leaking down. if the needle and seat leak any at all after you shut off the engine there is still pressure in the line between the pump and the carb and this will cause the fuel level to raise and leak out. this is why the later model corvettes have a return line from the fuel pump to the tank to relieve this pressure.

[Allan Hein]

Oil versus Gas Accumulation - Clem Z.

Clem: Your observation of the fuel versus oil leak better describes the problem I am encountering. The appearance of the liquid in the manifold depression does have a slight oil color, is thicker in texture than gas, but has the odor of gas. The liquid usually accumulates over a period of about a week of inactivity. I have ensured that the gas line fittings and carb gaskets are tight without excessive torque, but still encounter the slight deposit. Thanks for your insight as to the probable cause.
Allan. NCRS#36159