Question: Why do carb and tbi cars take awhile to fully warm up on cool days and auto shifts harsh until it warms?

(Posted by: jaymax173 on 2010-07-27 08:20:29)

Posted by: Alekat on 2010-07-27, 08:29:55

Many times - it is a thermostat that is defective and/ or contaminated, from inadequate system maintenance, causing it to not close completely. It has to close all the way or cold coolant is allowed to enter the engine via the lower hose preventing the engine from warming sooner. Most vehicle engines take 3/ 5 miles to warm at an ambient temperature of 70 degrees and the transmission takes at least 10 miles. Carburetor or fuel injection has nothing to do with it.

Posted by: Mad Jack on 2010-07-27, 08:28:30

Physics You must warm about 500 pounds (186 kg) of mass from the ambient outside air temperature to about 200F (93C). This will not happen instantly with the amount of fuel burned to operate the engine. The engine will not run correctly until it is up to full operating temperature. With an automatic transmission the torque converter will not fully lock until it receives a signal from the computer that the engine is up to full operating temperature. The computer may also alter the transmission line pressure while the engine and transmission is cold. This would explain the harsh shifts. If your engine takes more than about 10 miles (16 km) to warm up there may be a problem with the cooling system, mainly the thermostat. If the transmission is excessively harsh shifting before it reaches full operating temperature in about 10 miles (16 km) this could signal an impending transmission problem.

Posted by: donpat on 2010-07-27, 09:26:12

They are designed to operate best at a warm temperature. There is a considerable mass to get warmed up and it just takes time to get up to design temperature. You are similar. If you start running and are not properly warmed up, you cannot run as well and injury to muscles, tendons, etc. is far more likely. Cars in north have an electric plug to plug in to warm up before starting.