Burning the paint on the intake would be normal in the exhaust cross-over area. Since it only takes about 300 degrees to start paint discoloration. If you don't want burnt paint, you would need to use a completely blocked gasket for the heat cross-over passage. If the exhaust manifold heat riser is in-operative, and most often failed closed, then all the right side exhaust must flow through the intake, and out the left side, adding to the heat in the cross-over. Don't forget to check other engine conditions as previously stated, all important factors to check. Ya'll have a nice day, Dave.
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From: David Whitney <hazegreen66@xxxxxxxxx>
Hi, Greg --
It sounds like you may have a number of issues related to high under hood temperature. This could be an indicator of serious problems. If your exhaust gases are discoloring your intake manifold paint job, are they also causing the exhaust manifolds to glow and/or crack?
There are three main reasons why exhaust can get that hot:
1. Low octane gas in high compression engine.
2. Timing is retarded too much.
3. One or more cylinders running lean.
Please investigate these conditions and see if things improve. Start by pulling your plugs and look for yellow deposits. If you see any, you have excessively high temperature in that cylinder. You will probably notice discoloration of the exhaust manifold at the same cylinder.
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