Cooling Down Your Exhaust Manifolds

[The_Handier_Man1]

Original post made by:  HeavyHaulTrucker
Sent: 12/20/2004 9:17 PM

Sob, it looks like you are most concerned with the risk of cracking an exhaust manifold.  Well, I will tell you a little secret that most older truck drivers know but seems to have been lost on the younger crop.

On these older engines, it is important to give them a "cool down" period at idle to allow the engine heat to dissapate through both the exhaust and the radiator/ coolant.  You see, if you just shut off the engine, there is a "heat soak" factor -- you see it most prominently when you shut off your engine and your water temp gauge goes from 190 - 200 to 210 or more.  Well, it is even worse for exhaust manifolds -- they go from a running temperature of around 600 degrees to over 1000 degrees in a matter of seconds, then cool rapidly from there.  That is when your cracking is most likely to occur -- during this rapid cool down.

It is better, and you are more likely to avoid manifold cracking, if you let the engine idle for a few minutes before shutting it off.  This allows the manifold to cool to around 300 degrees with the cooler exhaust gases of idle -- then, when you shut it off, the "heat soak" won't be so drastic.

This was an old lesson learned on the old 855 cid Cummins diesel engines, when shutting it off suddenly could crack a block, head or cylinder liner.

John



From: ProactiveEdBrady
Sent: 12/20/2004 9:31 PM

You mean I've been doing it "wrong" all this time?  I NEVER shut down the Whiny Beggar when I get to whatever spot.  I leave 'er running until I have everything hooked up, and then shut her down.  And, I suppose that takes me five-ten minutes.  (Gee!  I've been doing it right all along and never knew it!)



From: cooneytunes
Sent: 12/20/2004 9:37 PM

John's 100% right with this especially comming in from an Interstate or High speed highway/freeway....most people only think you have to do this with a diesel....the main reason on a diesel  with a turbo charger, the turbo charger will be spinning at highway speed for up to three minutes and with out the engine running, it has no lubracation, and no way to cool off like John said, but it's also relevant in gas model engines, to let some of the metal parts disapate the high temps and cool down a little before you shup it off, cool down is also good for the valves....Also on the exaust note.... I think the main reason people also have some troubles when booting up to a larger exaust is, (Now correct me if I'm wrong) when you go larger or add headers, you change the back pressure on the engine. The engine was designed for a certain degree of back pressure, and a change, with out making outher changes,  carb asjustment, manifold, etc. will most times cause more problems. At least that is what I have been led to believe.....
Timmy



From: Liv42dayOK
Sent: 12/20/2004 10:34 PM

That tip was probrobly the very first valuable bit of information I learned from this web-group.  And it was none too soon before my first trip under mega-load going up a mega-hill on the way to the 1st NECWJ.  I let the Winnebeast run for about 15 minutes before shut-down.  Had Dave Denison and Lowell not shared that with me before hand, I very well might be sharing the pain of what it's like to change manifolds! - Sob



From: mightybooboo
Sent: 12/20/2004 11:25 PM

Very good advice about allowing a cool down,I sometimes forget that.Saw at 'Another Site' that lots of the old jockeys get off the freeway and putt-putt to the campground,actually they are doing that to cool down the rigs,and we always thought they were just ole' F@rts who couldnt get movin',not the case at all.
Lazy BooBoo