Ok, I understand what a redline is, it's there to make sure the engine doesn't rev past it's safe limit and destroy itself. But, recently I found out that most cars, including my 91 CRX, have a cold redline as well as a hot redline. Or to use more correct terms, a fuel cut-off. My cold fuel cut is at 6,000RPM, where the hot fuel cut is at 7,200 RPM. What I'm wondering is, when the engine is cold, does that 1,200RPM really make that much of a difference? Wouldn't it make more sense to set a cold redline much lower than the hot one? I dunno, I'm curious. Anyone know? Is it for reasons other than mechanical safety? Perhaps it has to do with effective fuel temperature and things like that? thanks

 

Engines have tighter tolerances and thus more internal friction when they're cold. The cold cut is designed to prevent excessive wear that could lead to engine failure.

 

Yes, 1200 RPM is a pretty big difference. 7200 is 20% higher than 6000. That's pretty big.

 

Two reasons for a cold redline - oil is still too thick and pistons have to expand enough so the skirts won't scuff or break from all the tipping they do in a cold engine. Revving a cold engine is one of the worst things you can do!

 

three very good reasons. Thanks!:thumbup: