Valve Cover powder coat bubbling due to blocked crossover ?

[Racer57]

I had my valve covers powder coated in two different colors by a quality outfit about 3 years ago. I noticed yesterday that they both had bubbles near the center above the Edelbrock logo. Its worse in the center(above crossover) and tapers off going outward in both directions and is only along the top edge. Passenger side appears to be worse.  After asking questions about my engine, powder coater said that since I have my intake manifold crossovers blocked, excessive heat is whats causing the problem. Powder coating is cooked at 400 degrees and they feel that the heads are reaching temps above that just enough to effect the coating. Engine water temp stays around 180-190.  I have no reason to doubt them, but I'm wondering if anyone else has had this happen to them ?
p.s. I have crossover blocked due to vapor lock issues with my Shaker and felt it would help. It appears to have helped but not 100% positive due to other changes made at same time.

[cudabob496]

looks to me that the powder coating was applied, or prepped, improperly, in some way.

[cudabob496]

https://vandacoatings.co.uk/blog/why-does-powder-coating-flake-bubble-chip-or-crack/

[Brads70]

I can't see the valve covers reaching 400 degrees. Around the exhaust ports on the cylinder head ok , but not the valve covers.

[Spikedog08]

I can't see the valve covers reaching 400 degrees. Around the exhaust ports on the cylinder head ok , but not the valve covers.

Yep I agree!   I suspect that it was not prepped properly . . . As cudabob stated above.

[Chryco Psycho]

Generally with the crossover blocked the heat cannot get up to the covers , with the crossover open there is a lot more heat moving through the head .

[RUNCHARGER]

I agree with CP: I don't think the temps would raise with the crossover blocked above what they were with it unblocked.

[Racer57]

While everything you guys are saying makes perfect sense, there's one thing that the powder coater pointed out that can't be ignored. Why is it worse directly above the crossover on both covers ? Its worse in the middle at the high point of the covers and tapers out from there, down to nothing within about 4in forward and back of the center.  Thats a hellva coincidence.  Like you guys, I can't see the covers getting that hot and I bought an heat sensing gun so I can get an idea of what kind of heat there is. I'm also going to pull the covers off in a day or so and look inside of them. 

[GY3R/T]

Cast aluminum is porous, holds lots of stuff, (oil )  It's coming out.

[cudabob496]

could always pop one and see what's underneath

[RUNCHARGER]

No denying that it would be hotter in the center of the head where the HR passage is and heat rises. I'm sure the center of the head is hotter than it is to the sides it's just I don't think it would be any hotter than in an application where the heat riser ports would be open.

[cudabob496]

looking underneath the cover, it would show, by discoloration, if the center was getting up near 400 degrees.

[Racer57]

I need to make something VERY clear. I'm intentionally leaving out the name of the company that did it. They do very good work and I feel that what has happen to mine is a fluke. No one is 100% sure about the cause so far. They have already offered a shipping label and will redo the powder coating for free. At this point only trying to figure out wtf happen and whether its worth the gamble of redoing these covers because of possible issue with the aluminum itself or getting new ones done.

[Shane Kelley]

I'm guessing it's do to porosity in the aluminum holding oil or contaminants.  A shop that does a lot of tig welding told me he has the hardest times welding aluminum when it has been oily before. He says it's almost impossible to get it clean enough.  If these are used valve covers it will probably do it again. When they bake these it might be releasing gases but not showing it's ugly problems till later. I have had good luck painting that type of valve cover. So that could be a option. 

[Racer57]

Here's pics of the bottoms. I suspect that since these were old valve covers the aluminum wasn't very good quality and allowed saturation after the powder coating was done.