'79 911SC Engine Heat Shield? Paint Going Bad

[79_911SC]

Hi Folks. I had my '79 911 SC repainted in its original Petrol Blue color about 10 years ago. Several years later, the engine lid displayed significant orange peel and has more recently shown bubbling of the paint.

The auto shop suspects this occurred due to high temps on the engine lid/deck. It indeed gets almost too hot to touch on a warm day after an hour's drive.

The auto shop uses high quality materials, the owner is a Porsche 911 enthusiast, and has repainted and restored a number of 911's. He has seen this problem before, and believes it's caused in part to within-modern-history CA EPA regulations to move away from solvent-based and leaded paints. He seems well versed in prep. and paint materials for galvanized surfaces. Is a pretty credible guy.

I'd like to know if anyone has experienced a similar problem, and has any ideas as to a suitable heat shield or other mods I might make to lessen the high temperatures that apparently are crinkling and bubbling the paint on the outside (but not the original paint on the inside) the engine lid. I don't believe there was any body filler needed on the outside of the deck lid prior to the last repainting.

I've search the forums, and there's plenty of posts related to heat shielding turbos, but that's not my problem. It's an all stock '79 3.0 CIS - no turbo.

Years ago, prior to repainting, removed the air conditioning compressor and condenser. Leaked like a sieve. A friend mentioned that perhaps this paint problem was not an issue with the original paint because the condenser functioned as a heat sink. I have no idea as to whether the presence/absence of the condenser would affect the engine lid temp/paint issue.

I've considered whether fashioning and mounting a sheet metal shroud to the underside of the engine lid might help (without, of course, covering the lid vent).

Any advice as to plausible engine lid heat shield solutions would be greatly appreciated. Or other ideas as to how to solve this problem.

The shop is going to repaint the deck lid soon. I'd hate to see this problem occur in another 3-5 years.

Thank you.

[Craig_D]

Pictures?

[kjchristopher]

What part of California do you live?
The Rust-Oleum I put on my ducktail has no issues with heat. If it is that hot, send something is amiss. Or you're in Palm springs in August. But even then....

[Driven97]

With the engine running, the engine compartment should be pretty much ambient temp. The fan is pulling a LOT of air in through the grille.

[gomezoneill]

If the paint on the inside is good and the outside bad then the paint job was done wrong.

[79_911SC]

Hi Guys,

Thank you for taking the time to reply.

-Craig_D - I'll post some pictures after work today.

-kjchristopher - I live in North County, Coastal San Diego (Encinitas). Not unbearably hot. But in even at 80 deg. F on a sunny day, after 10-15 minutes after turning the engine off, the center of the engine lid is basically too hot to keep your hand on it for more than several seconds.

-Driven97 - With the engine running, the engine lid is warm but not hot. Unless it's 90 Deg. F ambient (rare in coastal S Diego).

-gomezoneill - ya, that's part of my concern. The auto body guy believes its due to recent-history CA EPA-required reformulations in auto paint. Don't know.

Thanks again. Hope I can get some reasonable pictures after work.

[79_911SC]

Hi Guys,

I made several attempts to obtain a suitable photo of the engine lid paint/blister problem, and unfortunately, what I attached is not optimal.

But within the attached "Paint Distortion" photo, there's a blister with the distortion area about the size of a quarter in which the paint has lifted off the substrate.

When the lid is warm and the angle of the sun is right, it's easy to see. I guess that's why it bothers me so much. I can actually depress the blister with a finger. It's definitely getting ready to peel off.

I've also attached for your viewing pleasure (I hope) a photo of the car. Also an shot of the engine bay, in which there is nothing peculiar, other than the temporary absence of the air pump and removal of the air conditioning compressor.

In any case, I'm curious as to whether you might share an opinion about whether it would be worthwhile for me to fashion some type of sheet metal heat reflector or heat shield on the underside of the engine lid. Perhaps mounting it 3/4-1" below the underside of the engine lid, and of course not covering the grill.

Or are you feeling that this was/is definitely a paint prep issue? Like I mentioned before, the auto shop seems to be quite meticulous and knowledgeable. But anything can happen.

Thanks in advance.

[Jdub]

Great looking car. Can you get an infrared heat temp reader on the lid and get us a number? Also, what is the temp. on your oil temp, gauge just prior to shutting off? Mostly want to know your car is running normal temps, with oil out and back to the cooler verified.

I get the sense you respect the shop but do not think this should be happening. I anticipate you will be going halves with the shop to redo this with possibly a more heat-resistant paint if they can match it? Good luck.

[79_911SC]

Hi Jdub,

Thanks for the complement and your suggestion about the IR heat temp reader. I'll do that, and will hopefully have some temp data to report back within the next couple of weeks.

You hit the nail on the head with respect to the shop. I respect the shop but don't think this should be happening. I stopped by to speak with the owner, and he's working up an estimate. Agreed that he and I will probably split the cost of the respray.

Disappointing overall. After almost 40 years, the underside of the lid is fine. But I don't know enough about contemporary paint formulations and the impact of transitioning from solvent and nasty additives to water-based, EPA-compliant formulations.

If there's a paint expert who would like to comment on this, that would be welcomed. I know the shop uses PPG products exclusively. I wonder if the durability of the paint formulation was impacted by EPA-mandated formulation changes implemented a decade ago, when the engine lid and the rest of the car were repainted.