Exhaust Brakes and EGT?

[LRDG]

This may well be a stupid question Given that they have been around for some time and that with the Jacobs e-brake being MOPAR and Cummins approved, it very likely is, but the question still nags.



The exhaust brake works by restricting exhaust flow and creating backpressure in the engine. The question is whether there are circumstances when doing so will result in such an increase in exhuast gas temperature as to present problems and potential turbo damage? Better exhaust flow contributes to diminished EGTs, all other things being equal. So logic suggests that impeded exhaust flows should contribute to increased EGTs, all other things being equal. Is there some mechanism in the Jacobs e-brake set up that I don't get that deals with the "all other things being equal"?



I can understand that in open road conditions the flow interruption is such that it is unlikely to have any significant impact. But when the e-brake comes into its own is in conditions that suggest there should be a problem. Towing in mountainous/hilly conditions. This puts a lot of stress on the engine, many people may be running boxes that further increase EGTs, and the e-brake is regularly working quite possibly taking EGTs above a safe level. So the final question is what's wrong with this picture - what's missing that explains why that would not be the case?



I must be wrong, but I'd like to know why... .

 

[Thomas]

... So the final question is what's wrong with this picture - what's missing that explains why that would not be the case... #ad

The exhaust brake doesn't stop the exhaust - it only restricts it. A properly functioning brake is only applied in a non-fueled condition. No fuel=no heat added. The exhaust passing the brake in the unfueled condition is relatively cool.

 

[LRDG]

Thanks Thomas. It seems rather obvious when you put it that way Well I knew I must be wrong - and now I know why

 

[EBung]

I had a exhaust brake on my truck and it did in fact raise temps when initially engaged but not to the point of it being excessive.

 

[SRadke]

Think of the brake as a butterfly valve in the exhaust pipe. When it's off you have a 1/4" thick rode extending across your exhaust pipe (through the middle). When you activate it it swings shut and almost compleetly blocks off the flow of exhaust. Do you have higher egt's when it's activated? Yes. At idle you'll have about 250° egt's, at idle with the brake on 400-500°. Since it should only be on while the engine isn't fueling you've got no temp issues.



It is not a good idea however to go screaming up a hill at 1400° egt's adn at the moment you reach the top flip the brake on and roll the entire way down teh other side without turning it off. You've basically trapped all this really hot air in your engine and you're not letting it out. Cycle it a few times on the way down and think ahead a little when you're nearing the top. You're turbo will thank you.



-Scott

 

[Joe G.]

If the exhaust brake fails so it sticks shut EGT will go through the roof. So will the amount of black smoke. I had the little vacuum solenoid stick on my '95 and that's what happened. I clean the solenoid every so often now. If you don't use the exhaust brake very often it may coke up and stick.