I'm helping a friend with his 350. Cleaning up the intake (after several years of sitting) we popped the stamped steel cover off the bottom side and found a lot of baked on oil crud.

What exactly does this cover plate on the bottom of the intake manifold do? (other than catch oil and bake it) Only thing we could think of was it is a heat shield of sorts. It's got a small hole at the lowest point of the plate, we guess to drain oil out of it (doesn't seem to have worked very well), there are no holes in the manifold under the plate. Can he leave it off?

Here's what we found under it, so you can see why he wants to leave the plate off.


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Bruce

 

It shields the oil from the heat of the exhaust cross-over when the EFE valve is closed, and shields the intake from hot oil during fully-warmed operation.

Use of cheap petroleum oil with high levels of viscosity index improver and infrequent oil changes lead to those deposits. The shield kind of collects the ruined oil. Use a quality synthetic and the shield will be able to do its job properly without those deposits.

 

My question would be what does the the rest of the engine look like?

 

Yuck!
I've pulled apart a few motors where the entire lifter valley was filled with that stuff, but the motor still ran OK.

Since it is just a heat shield, and aftermarket manifolds do not have it, my guess is that you will be OK leaving it off.

 

Leaving the heat shield off is not the solution.

If he leaves it off, the oil will be splashed up onto that hot surface, and get heated up. The temp of ALL the oil will be substantially higher as a result.

A better solution is to clean it up, put the heat shield back, and then change the oil on a regular basis in the future.

 

I'm sure you are correct. The oil will get hotter. I just wonder how much? What do you mean by "Subatantially"?

On the one hand, I know GM wouldn't pay to put something on if there wasn't a reason.

On the other hand if you are heating up the oil aren't you cooling the intake manifold? For that matter what if the entire passage were blocked at the manifold gasket? Then the oil might heat up the manifold instead of the other way around...OK, I know I'm drifting off on a tangent.

 

Well, if you blocked off the exhaust passages, then there wouldn't be that heat.... but, then the oil would be heating up the intake more. Racers use the shield, or even buy an aftermarket one with a similar function such as this to help keep the intake charge cool, if they can't use an intake with the plenum isolated from the base for whatever reason.

Either way, the shield is a good idea (keep the oil separate from the intake for temp reasons), and should be retained if possible.