Throttle Plate Corrosion/Gasket

[secondchance]

Like so many LT5s my 94 had developed corrosion around the edge of plate on the throttle body side. This necessitated scraping off of bubbling area and refinishing. In my opinion, even if this area is re-powder coated, galvanic corrosion if not stopped will result in bubbling just the same. However, some LT5s seem to be immune from this phenomenon perhaps due to low mileage.

Last time I had a brief discussion with Marc Haibeck when I met him at Carlisle. In his opinion this corrosion was due to plate gasket being made of paper would soak with coolant eventually allowing galvanic corrosion and suggested only way to stop this would be to bypass coolant.

In my case, I prefer not to bypass the coolant in order to keep it looking stock and also because I drive the car even during the winter months. Therefore, I elected to come up with a solution to deal with this corrosion issue.

Then about 3 weeks ago during a get together with the WAZOO guys I had a chance to discuss this issue with a nuclear engineer and a chemical engineer. Interestingly the chemical engineer was one on the guys who was employed by GM back in the early 70s to develop catalytic converter.

After a few minutes we concluded that the coolant was acting as the electrolyte, quite obviously, either and or both the plate (possibly an aluminum alloy with other metal) and steel bolts holding the plate was the anode and throttle body was the cathode where ions from the anode was being deposited.

Then, if I can isolate the plate and bolts from the coolant, the electrolyte, this corrosion can be contained.

Best way to achieve this would be to come up with non paper gasket material and allow the gasket to span the entire opening so that the plate would not come in contact with the coolant at all.

Then I turned to water proof membrane sales rep and he suggested "Hyproof GL". This product, manufactured by Hyload, was developed as a roofing membrane for structures where fumes from oil, gasoline, jet fuel, glycol and other chemicals were of concern. Also, manufacturer claim that it can be used in environment below 375 degres farenheit.

I finally got hold of sample sheets of this product and will have it installed in my car sometime this week. Only problem is that I will not know if I am right for at least another 60-70,000 miles.

[QB93Z]

SC, Is the membrane material thin enough to use for a gasket? I don't think that high milage alone accounts for the corrosion. My cars, 104K, 94L and 74K miles do not have corrosion around the throttle body plate.

Jim

[tomtom72]

Yun, I'm with Jim on the milage thing. My car had it when I took delivery of it. The car only had 7400 miles on the clock.....spread over 14.5 yrs., and the O.O. said he did the coolant sys service every two yrs without fail.

I did my clean up on my T/B pox back in 10/05 @ about 12 or 13 k miles. Now at 39k miles in 10/09 I have no return of the pox.

I used the standard replacement gasket that came in the "top end gasket kit" from one of our suppliers. The gasket is just paper? I know it's not cork or some type of rubber. All I did was coat all sides using my finger ( GM tool # J-001 ) with rtv from permatex. I did coat the insides of the screw holes on the gasket, and proly got some on the screw threads also. The plate's roof is exposed as the replacement gasket is configured just like the OE gasket.

I'm not even sure that just the gasket being made impervious to water penetration is the whole answer. There has to be a "stray current" introduced some how. That leads me to think that all the grounds on the block and frame in the engine room need to be 100% also? JMHO


Tom

[secondchance]

Jim,

I know some cars do not have this problem. Could be minor variation in various grounding where some do not have stray current flow around the throttle body.
Unfortunately, both cars I have owened had this issue. My 91 started to show bubbling at around 70,000 miles. Current car, 94, I can not recall when this started to show.

Membrane is 1/16" thick coal tar elastomeric (CTEM) waterproofing membrane. Its primary components are coal tar pitch, PVC, and Elvaloy (whatever that is).

Tom,

I agree with you in that there must be a stray current. Nonetheless, cutting out electrolyte should mitigate corrosion. Don't you think?

Also, yesterday I boiled this thing in water (higher boiling point than glycol mixture I think) for a while. It did get softer but did not disintegrate.
So, as soon as I run out and get a hole punch (for screw holes) I am going to fabricate a sheet and give it a shot.

It is one of those things where I will be waiting for a sign that I hope not to see.

[tomtom72]

Yun,

I would say that any thing is better than the protection that exists with the gasket installed in the OE configuration.

I still think that all the grounds are more important. JMHO

The one thing that I noticed with all the grounds that I could get to, they all were dirty! I used Gordon's INFLREST correction on every ground that I could find. I actually believe that is what stopped the pox, and not all my rtv on the gasket. I'm sure that the rtv had a helping hand, but the stray currents have to be stopped. JMHO


Tom

[secondchance]

Originally Posted by tomtom72

Yun,

I would say that any thing is better than the protection that exists with the gasket installed in the OE configuration.

I still think that all the grounds are more important. JMHO

The one thing that I noticed with all the grounds that I could get to, they all were dirty! I used Gordon's INFLREST correction on every ground that I could find. I actually believe that is what stopped the pox, and not all my rtv on the gasket. I'm sure that the rtv had a helping hand, but the stray currents have to be stopped. JMHO


Tom

I guess I will have to get under and check/tighten all grounds.
Thanks.

[tomtom72]

Originally Posted by secondchance

I guess I will have to get under and check/tighten all grounds.
Thanks.

Yun, this is a fwiw on squaring away the grounds. It's tedious at best. I used the following:
s/s bristle small brush
brass bristle small brush
dielectric
star washers
contact cleaner spray
120 grit sand paper or those 3M scrubbers...whatever was handy.

discon ground wire(s), clean wire eyes & bolts & attachment point to bright finish. Stingy dab of dielectric, star washer, eyes, star washer, another stingy dab of dielectric, bolt back in thru the whole mess!

Also fwiw, I pulled apart the electrical connectors and rubbed dielectric into those rubber gaskets on the male side. Oh and I cleaned up that "distribution block" ( down below & aft of the battery ) as those eyes & posts were ragged looking on my car. The star washers will not fit there though, space too small. There is some kind of drain tube that was pointed right at that block in my car so I moved it.

The thing is, I can't really say if any of this actually did anything.

[secondchance]

I know what you mean.
And you are waiting for something you hope will never return!
Thanks for the tip. Perhaps it's a lot easier to hold on to extra paint and just redo the TB if and when it bubbles up in, what 2 years? 4 years? Never???

[flyin ryan]

Originally Posted by secondchance

I know what you mean.
And you are waiting for something you hope will never return!
Thanks for the tip. Perhaps it's a lot easier to hold on to extra paint and just redo the TB if and when it bubbles up in, what 2 years? 4 years? Never???

Aahhh...one of the joys of owning a Zee

[secondchance]

Originally Posted by flyin ryan

Aahhh...one of the joys of owning a Zee

Only reason I own a Z (total of 14 years) is the joy outweighs the misery.