Downshift on uphill while towing
Super Moderator
Joined: Aug 2003
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From: Isanti, MN
Not by very much. Assuming a constant air/fuel ratio, air consumption will remain equal at different RPMs if it's making the same amount of power. Greater parasitic losses at higher RPMs will make it consume more air and fuel per unit of power output to the transmission, but not a whole lot. Manifold vaccum will increase as engine load decreases after the downshift. Less pressure entering the cylinder means lower volume per stroke.
Moderator
Joined: Jul 2011
Posts: 6,506
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From: Sioux Falls Area
Not by very much. Assuming a constant air/fuel ratio, air consumption will remain equal at different RPMs if it's making the same amount of power. Greater parasitic losses at higher RPMs will make it consume more air and fuel per unit of power output to the transmission, but not a whole lot. Manifold vaccum will increase as engine load decreases after the downshift. Less pressure entering the cylinder means lower volume per stroke.
more air pumping through the engine does not mean more cooling unless that air is not creating heat as it goes through, which unless the engine is shutting down cylinders, the air is being used to make power and thus creates heat.
i wasn't supporting the argument, just trying to re-state it.
Cargo Master
Joined: Apr 2007
Posts: 2,659
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At low rpm the engine is loaded down hard, it is running rich, timing is retarded, and exhaust gas temps are running high. It is no wonder why the engine is hot. Changing gears alters all those things in a good direction and also reduces the load on the engine.
Cargo Master
Joined: Apr 2007
Posts: 2,659
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Exactly. We all know the answer is to shift gears and even crank up the heater if you have to. If that doesn't do it then either stop, or turn around and run downhill to push air through the radiator and keep engine at mid-rpm's to get radiator side coolant through the engine quickly.
My buddy had a Dodge minivan that was overheating on a climb in Nevada. He didn't know what to do. Just kept driving. Finally I told him he had to turn this train around or something bad was going to happen. He listened, flipped a quick U-turn, and temps were under control in about 30 seconds. Car was barely crawling up the hill in the first place so there was no second attempt to summit.
My buddy had a Dodge minivan that was overheating on a climb in Nevada. He didn't know what to do. Just kept driving. Finally I told him he had to turn this train around or something bad was going to happen. He listened, flipped a quick U-turn, and temps were under control in about 30 seconds. Car was barely crawling up the hill in the first place so there was no second attempt to summit.
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