IIRC my almost full fills (aprox 1.25" to 1.5" down from deck surface) never really had a problem with overheating the cooling system side of the equation. This was especially true when using an electric waterpump/electric fan setup. After a pass It would cool down almost as fast as it would without grout.
And when I used a mechanically driven waterpump/fan setup I still didn't see any problematic cooling system overheating during a pass/runtime. But I have to admit with a mech WP setup the engine/grout/cooling system did hold onto the generated heat a lot longer after shutdown (vs a "no grout" combo) because of no moving water after shutdown to help cool the grout surfaces.
Grout will almost always increase engine oil temps/thin the oil a given amount since there is no circulating water in the bottom of the block/waterjacket to help carry away some of the heat from the hot splashed oil contact & oil pan mating surfaces. The increased oil temps aren't usually a problem on a race-only deal unless you end up with some scary low oil pressure numbers at idle on the return road after a pass. Thicker oil or more oil pressure (shim the pump spring, or stiffer spring) can be used help boost the hot oil/thin oil pressure numbers after a pass.
On a grouted street combo you could also as mentioned add an oil cooler to the mix to help cool the oil/boost the hot pressure numbers. But to be honest I really don't like the idea of using grout on a "true" street car (one that will actually see extensive "real" street/highway use). This is because both cooling system types (elec driven & mech driven) can sometimes have drawbacks when used with grout on the street (even with a low height grout fill). With a mechanically driven cooling system the grout will always cook the crap out of the head gaskets, heat-soaking them for a long period of time after shutdown, especially with the extra heat build-up of street driving. And I have never liked using an electrically driven cooling system on the street (with or without grout). They are great in a race car, but IMO just don't ever seem to really "keep up" with actual changing engine RPM vs water flow demands on the street.
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