Well heat is determined by coolant temp so start there. How long does it take to get to 60 degrees? How long to 80? If this is taking a really long time then the thermostat could be stuck open causing the coolant to flow continuously through the radiator, causing the engine to warm up slower. The thermostat is there to help the engine warm up more quickly by bypassing the radiator so it will not cool the coolant. Then as the engine reaches temp and the coolant is above 87 degrees the thermostat opens, this keeps the coolant at or around the thermostat temp. Unless of course the air outside is too hot or you are idling to long and the coolant is not cooling below the thermostat's set temp. Either way, if it is stuck open then of course the coolant heats up slower and thus the heater takes longer to have warm fluid passing through the core.

Or it may be a vacuum pod bad or leak inside causing the vacuum element in the blend air section to not open properly or hold open enough. This is of course assuming that the coolant is coming up to temp in time and a good functioning thermostat. And also assuming that the heater valve is not stuck closed or malfunctioning as well.

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....