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Old 01-23-2022, 06:33 PM   #1
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Exhaust manifolds

Iím hearing people getting cracked (cast iron) exhaust manifolds. In all vehicles when under load and you pull in and shut it off, the exhaust manifolds could even be cherry red. They are too hot to shut the engine down. I always sit and let it idle, momentarily accelerate the engine to 1,250 -1,500 rpm and back to idle so the exhaust gases which will be cooler, that they cool the manifolds. RV, car, truck, turbo engines - this method should prevent the problem of having a cast iron exhaust manifold crack as well as in the turbo engines, prolong the turbo life also. Happy motoring!
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Old 01-23-2022, 06:55 PM   #2
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Exhaust Manifolds/turbos should be cooled by the time you pull in

Unless you are pulling hard on Interstate and pull right off into a rest area....then a few minutes of IDLE will cool it all down
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Old 01-23-2022, 07:00 PM   #3
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Iím hearing people getting cracked (cast iron) exhaust manifolds. In all vehicles when under load and you pull in and shut it off, the exhaust manifolds could even be cherry red. They are too hot to shut the engine down. I always sit and let it idle, momentarily accelerate the engine to 1,250 -1,500 rpm and back to idle so the exhaust gases which will be cooler, that they cool the manifolds. RV, car, truck, turbo engines - this method should prevent the problem of having a cast iron exhaust manifold crack as well as in the turbo engines, prolong the turbo life also. Happy motoring!
I agree, it's always best to let an engine idle for a few minutes and dissipate some heat if it's been working hard.
I wouldn't rev a turbo motor though. Turbo's spin pretty fast, and you want them to coast down to the lowest possible RPM before shutting down the engine and their oil supply.
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Old 01-23-2022, 07:58 PM   #4
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2 to 3 minute cool down has always been my rule
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Old 01-23-2022, 08:11 PM   #5
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Good advice to let things cool before shutdown.

My personal practice is to always let my diesels fall to 300 degrees EGT or less before shutting them down.
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Old 01-23-2022, 08:44 PM   #6
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I’m hearing people getting cracked (cast iron) exhaust manifolds. In all vehicles when under load and you pull in and shut it off, the exhaust manifolds could even be cherry red. They are too hot to shut the engine down. I always sit and let it idle, momentarily accelerate the engine to 1,250 -1,500 rpm and back to idle so the exhaust gases which will be cooler, that they cool the manifolds. RV, car, truck, turbo engines - this method should prevent the problem of having a cast iron exhaust manifold crack as well as in the turbo engines, prolong the turbo life also. Happy motoring!
Well,
Been camping and RVing for oh, maybe almost 40 years with 2 different truck and campers, and 4 different motorhomes. NONE of which EVER developed any cracked manifolds. The first truck was a '79 F-350 with that great 460 cu.in. in it. What an outstanding motor. The second truck an '86 F-350 Crew cab dually with that junk, naturally asperated 7.3L Navistar. It couldn't get out of its own way. Then a dodge class C with the 440,. a Ford Class C with the 460, a Class Bounder with the 275hp V-10 and now, a 36' Class A with the CAT C-7 330HP.

The first thing to think about here is, out of the 10 zillion motorhomes etc. that out there traveling the U.S, just how many have developed a cracked manifold? The second thing is, you're not gonna have a "cherry red" exhaust manifold when you pull up and stop, unless you just climbed the tallest grade around for 10 miles and it was 110 degrees outside and you're max loaded. Normal traveling down the road, even on a flat freeway, with a ton of air circulating around that engine, won't get those manifolds over heated. Hot, but not overheated.

Of course the engines and related components get hot, no doubt about it. But to get the manifolds cherry, is tough to do. And yes, if you've labored your coach on a long grade and you pull off that grade or freeway and your campground is right there, like some are, OF COURSE the smart thing to do is let it idle for at least a few minutes. But, if you've labored that coach engine and pull off, and your campground or destination is say, a couple of miles down a flat easy going 20-35 mile an hour road, your engine will had cooled plenty by the time you reach your stopping point. It's all about a bit of common sense.
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Old 01-23-2022, 09:53 PM   #7
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Its more likely that you'll have broken manifold bolts than a cracked manifold, but it does happen. Particularly in the rust belt where the salt has eaten it away a bit. On the Ford V10 for example, the bolt is only 8 mm as in years back they use to be 3/8th inch. I'm getting ready to do that job right now in fact.
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Old 01-24-2022, 04:54 AM   #8
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I agree, it's always best to let an engine idle for a few minutes and dissipate some heat if it's been working hard.
I wouldn't rev a turbo motor though. Turbo's spin pretty fast, and you want them to coast down to the lowest possible RPM before shutting down the engine and their oil supply.

I was baffled by that as well. I have never heard of that for any engine or any manuals saying that.
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Old 01-24-2022, 09:10 AM   #9
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"But to get the manifolds cherry, is tough to do." Umm, no it's not. It happens more than you think you just don't see it. I can make the exhaust pipes on one of my motorcycles glow orange enough to light a cigarette off (and win a $20 bet) just by standing next to it and working the throttle inappropriately a few minutes after tweaking the mixture a tad rich,
A dark cherry glow on exhaust manifolds will be next to invisible in daylight. An IR gun or camera tells the tale though. People who work at quickie oil change services have seen more than a few glowing manifolds.
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Old 01-24-2022, 12:13 PM   #10
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Quote:
Originally Posted by 30B Steve View Post
Iím hearing people getting cracked (cast iron) exhaust manifolds. In all vehicles when under load and you pull in and shut it off, the exhaust manifolds could even be cherry red. They are too hot to shut the engine down. I always sit and let it idle, momentarily accelerate the engine to 1,250 -1,500 rpm and back to idle so the exhaust gases which will be cooler, that they cool the manifolds. RV, car, truck, turbo engines - this method should prevent the problem of having a cast iron exhaust manifold crack as well as in the turbo engines, prolong the turbo life also. Happy motoring!
Hi ! Welcome to IRV2! We're sure glad you joined us!

I always let my engine run for a few minutes after pulling into the campsite. Better safe than sorry!

Good luck, happy trails, and God bless!
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Old 01-24-2022, 12:17 PM   #11
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Actually, after pulling off the highway and idling while checking into the CG, when you get to your site, you are good to just turn it off.


MAX time to idle to cool down if you have really been working the engine hard would be 5 minutes-- yes MAX.
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Old 01-24-2022, 02:57 PM   #12
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The 454 in the Winnie cracked the driver's side manifold. Chevrolet recommends that the head-side webbing be cut in the center if they are removed, and on replacements, to prevent cracking. (That's enough to make me wonder why they weren't cut when bolted on to start with, but whadda I know?) We traded it in with the cracked manifold, so I never fixed it.
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Old 01-28-2022, 07:04 AM   #13
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I found that my 7.4l Chevy had a LH cracked manifold when I pulled the heads of last spring. So it makes me think there are a lot of MHs driving down the road with a cracked manifold but the owner doesn't even know it. It was just a hairline crack and not making any noise. Besides cutting the webbing I also read somewhere a recomendation (I don't believe it was GM) that the bolt holes be enlarged slightly in order to accomadate for more movement. Do any of the elder folks remember there parents and others reving the engin nearly wide open and shutting the key off quick when shutting down.
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Old 01-28-2022, 08:58 AM   #14
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There are companies making and selling jigs to aid mechanics in the drilling out of broken exhaust manifold studs on newer pickup engines. They have kits for. Fords, Chevys, and Dodges. They all do it. They used to crack the manifolds, now they shear the bolts. Just a thing and you can't really point fingers at this or that brand.
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