Jake-Brake/Engine fan engaging

Sorry mate but you've got that one wrong. The only reason to bring the fan on with the jakes is to increase braking force. The reason it waits a few seconds before coming on is to save the fan clutch from excessive cycling if you're on and off the jake a bit in traffic etc.

 

I would like anyone to explain how the Fan increases braking. The engine fan comes on because the engine is working as hard on compression going down hill as hard as it is pulling when going up hill. The fan only helps dissipate HEAT. If your fan is pulling 50 hp from your engine, you better get it fixed.

 

The fan increases braking by putting an extra load on the engine and in a condition where the truck (load) is trying to push the engine the fan adds extra resistance.So if you combine the engine brake with the fan coming on you have more braking power,I believe the engine manufacturers call this "dynamic braking".
A fan does in fact use horsepower,I have seen a loss of 30/35 hp at the wheels with a truck on a dyno and why companies like Horton are always working to develope more efficiant fan designs.FYI any accessory powerd by the engine alt.,a/c comp. power steering takes power from the engine when being used.Ever been driving in traffic in a lower gear in the summer with the a/c on?Ever wonder why when the engine fan comes on you can feel a momentary pull on the truck.....that because of the extra load being put on the engine.

 

Have you ever noticed how when you are pulling up a steep grade and the fan kicks in that sometimes you need to down shift half a gear???
Thats telling me that the fan is robbing HP to drive it......no?

Also when I'm on the jakes down a steep hill it makes no heat it only makes heat when you add fuel,so there is a little difference in how hard the engine is working from uphill to down hill.

How much HP dose it take to drive the fan in your opinion????

 

That's spot on. How much power a fan draws depend on the design, most trucks I see lose around 20rwhp with the fan on but Acert/EGR engines throw out more heat and require a more agressive fan so they would therefore draw more horsepower, also some manufactures spin the fan faster (different sized pulleys) so that would make them take more horsepower.
Also, on Cats at least, you can turn the fan off with the jake in the ECM. If the fan with the jakes was required to keep the engine cool then you wouldn't be able to turn it off in the ECM.

 

Detroit calls the option of using the fan with the engine brake dynamic braking and it is an option that can be turned on or off in the ECM.Another point to the concern that the fan stays on after the engine brake has been used is that it is likely the "fan on" time setting when turned on by the ECM that is causing that situation.The fan on time may be set to 90 sec.when turned on by the ECM,so if you only had used the engine brake for 60 sec. it would stay on for another 30 sec. You see this alot when the ECM turns on the fan while using your a/c and depending on the time setting is why it stays on so long.This can be changed but in a Detroit,I'm sure a dealer may be able to access the setting if not they may have to ask the factory to change it.

 

the only time temp goes up down a grade is if the tranny's oil cooler is a coolant type so the increased heat will raise coolant temps down a grade

 

If you knew how an engine brake works you'd know it doesn't build heat ...theres almost no fuel what so ever being pumped into the cylinders and no combustion is occuring your engine should cool down while the engine brake is on. The reason the fan comes on is because it's an extra feature in the ecm that can be programmed to give an extra 50 to 75hp worth of braking power...

 

Reviving a nearly 14yr-old thread? You must be bored, today.

 

And wrong, too!

A steep, extended decent on the Jake will indeed bring up the water temps enough to kick in the fan. Yes, the engine isn't burning fuel, but it is still doing work. There isn't the excess heat of combustion inefficiencies, and much of the heat is dumped in the exhaust pulses, so it takes much longer to warm the engine than a climb, but warm the engine it will!