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How hot do cast iron exhaust manifolds get?
Posted By: BDW
How hot do cast iron exhaust manifolds get? - 12/11/08 02:14 AM
I painted my 340 stock exhaust manifold with hi-temp paint and it blistered as soon as I fired the motor up?
I wired brushed off all surface rust, hit it with some Ospho, then painted.
What went wrong?
Posted By: fjr340gts
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 02:38 AM
I measured mine with a laser pyrometer and they usually are in the 460-520* range
Posted By: earlybee
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 11:51 AM
Quote:
I measured mine with a laser pyrometer and they usually are in the 460-520* range
They get hotter than that under load.
Posted By: dmerc
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 11:55 AM
I did the same thing and get about 800-850 degrees at idle. I'm sure it goes way up under full throttle. I guess there are spray paints that will stay on but I've given up painting my manifolds. It's kind of like trying to keep the bottom of the car clean. If you drive it it's going to get dirty and natural colored manifolds really don't look bad at all.
Posted By: lewtot184
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 02:28 PM
the 440 in my '69 r/t varies from 550f at #1 cylinder to 650+f at #7 under very moderate driving conditions.
Posted By: ScottSmith_Harms
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 02:37 PM
Skip the paint. First you must remove and media blast the manifolds clean,then wipe them down with a liberal coat of clean 90 weight (yes, it's a nasty mess) wipe them off, put them on the engine, and run them until it all smokes off. It stinks to high heaven so be sure to do it away from your place. You can also cook it off prior to assembly with a propane torch, either way works about the same. The raw cast iron will take on a nice mellow brownish gray color and won't rust for ages, a light spot touch up with a wire brush and more 90 weight during the first year will keep rust at bay for many years, the results are pretty amazing.
Posted By: RapidRobert
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 04:26 PM
Quote:
Skip the paint. First you must remove and media blast the manifolds clean,then wipe them down with a liberal coat of clean 90 weight (yes, it's a nasty mess) wipe them off, put them on the engine, and run them until it all smokes off. It stinks to high heaven so be sure to do it away from your place. You can also cook it off prior to assembly with a propane torch, either way works about the same. The raw cast iron will take on a nice mellow brownish gray color and won't rust for ages, a light spot touch up with a wire brush and more 90 weight during the first year will keep rust at bay for many years, the results are pretty amazing.
That is so unconventional that I'm just going to have to try it 
but 1st I'm going to try some black barbeque grill paint.
Posted By: hooziewhatsit
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 05:03 PM
Sounds like the method (sans the 90wt
) to season a cast iron skillet. That should work great.
-Dave
Posted By: Rug_Trucker
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 05:56 PM
That is so weird Scott! Wonder if that would work on headers?
I am tired of spraying Plasticoat white on the Hookers.
Isn't there a coating that Eastwood or somebody sells?
Posted By: RapidRobert
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 07:31 PM
Quote:
Isn't there a coating that Eastwood or somebody sells?
yeah but I dont know how good it is though
Posted By: ScottSmith_Harms
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 07:48 PM
In my own experience it works best on cast iron but many other metals as well. I didn't invent the method, Mike at Rcket Restorations showed it to a while back, works great for treating cast iron of all types when you want a more original appearance (as opposed to painted which is never "correct").
Posted By: MoparforLife
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 08:07 PM
They get hot enough to cook on.
If you are looking at an original look, leave them natural cast.
Posted By: MoparKansas
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 09:07 PM
Calyx (sp? keeps them looking nice, but a little too shiny for stock cast iron. It also will rub off somewhat for a while. My brother has it on his car and hasn't had it bake off yet...
http://www.calyxmanifold.com/
Posted By: BDW
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 10:21 PM
The 90w does sound unconventional! I might just have to try it. I'm still curious what happened with the paint. It started separating as soon I fired the motor up! It actually looked like there was a latex glove on it and was being blown up. For some reason the paint didn't even attempt to bond with the metal.
Really frustrating.
Posted By: 1MYTGTX
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 10:31 PM
FWIW I had mine Jet-Hot coated and have looked like this for the past 5+ years now...reduced the underhood temps as well
Posted By: BDW
Re: How hot do cast iron exhaust manifolds get? - 12/11/08 10:45 PM
Looks nice, where did you have it done & how much did it cost?
Thx
Posted By: rss
Re: How hot do cast iron exhaust manifolds get? - 12/12/08 01:14 AM
Quote:
I wired brushed off all surface rust, hit it with some Ospho, then painted.
I'd bet it has something to do with the Ospho. Probably hadn't fully cured so you had some moisture trapped under the paint that bubbled once you heated them up. 
Posted By: BDW
Re: How hot do cast iron exhaust manifolds get? - 12/12/08 02:35 AM
Your probably right, but it might have something to do with cleaning it with easy-off oven cleaner initially. I thought I rinsed it well, but maybe not enough? After letting them dry for a day I then used a wire bush on a drill to clean it up further. I then put on the Ospho. Manifold actually sat then for a week at this point(I had to go out of town on business).
After painting, I set it out in sun for 2 days.
But it must have been some sort of trapped moisture, that paint didn't last 10 seconds!
Posted By: fjr340gts
Re: How hot do cast iron exhaust manifolds get? - 12/12/08 03:50 AM
I had mine coated. The inside with a thermal barrier, and the outside with a cast iron gray coating.
Cost about $150 for the pair.
www.automotivemachine.net did the process.
Posted By: GoodysGotaCuda
Re: How hot do cast iron exhaust manifolds get? - 12/12/08 03:53 AM
Quote:
but 1st I'm going to try some black barbeque grill paint.
..dont even waste your time.
Posted By: RapidRobert
Re: How hot do cast iron exhaust manifolds get? - 12/12/08 04:08 AM
it wont even work with good prep? When I'm flame broiling my steaks it get pretty hot.
Posted By: GoodysGotaCuda
Re: How hot do cast iron exhaust manifolds get? - 12/12/08 04:15 AM
i've prepped the heck out of two sets of headers. Well, short of media blasting, the paint hasn't held up for more than 3-4 months of weekend use.
Posted By: goldmember
Re: How hot do cast iron exhaust manifolds get? - 12/12/08 04:19 AM
Thermal coating is the best if you want it to last.I have mine done locally.
Posted By: RapidRobert
Re: How hot do cast iron exhaust manifolds get? - 12/12/08 05:01 AM
Quote:
i've prepped the heck out of two sets of headers. Well, short of media blasting, the paint hasn't held up for more than 3-4 months of weekend use.
alright I'm convinced. I will explore another option
Posted By: MO_PA
Re: How hot do cast iron exhaust manifolds get? - 12/12/08 12:21 PM
Quote:
Skip the paint. First you must remove and media blast the manifolds clean,then wipe them down with a liberal coat of clean 90 weight
I agree with Scott's oil treatment except I use ATF instead of 90 Gear oil, the ATF leaves a blueish tan/gray and it last a long time.
Posted By: 360view
Re: How hot do cast iron exhaust manifolds get? - 12/13/08 04:42 PM
850 sounds about right for an engine that has been running for awhile
I have not measured more than 1280 F
at short bursts of full throttle
at the hottest cylinder
on a 1995 360,
but I would guess in the worst case
it would approach 1500 F on the inside of the manifolds
and perhaps 1400 on the outside
The black magnetite coating
(like on impact sockets)
that people are trying to make on the outside
using the oil coating will break down at those 1200 to 1400 temperatures
$150 for a thermal barrier inside and another anti-corrosion coating outside sounds like a great bargain to me for a pair of manifolds
Posted By: ScottSmith_Harms
Re: How hot do cast iron exhaust manifolds get? - 12/13/08 05:24 PM
Quote:
The black magnetite coating
(like on impact sockets)
that people are trying to make on the outside
using the oil coating will break down at those 1200 to 1400 temperatures
Maybe true but in real world testing I haven't seen it breakdown much at all, as I mentioned a light periodic touch up is all it takes.
Posted By: moper
Re: How hot do cast iron exhaust manifolds get? - 12/13/08 05:38 PM
The ATF/oil treatment has been around for a long time. I used it back in the 80s. I don't even bother anymore...lol. No car ever looked that way on the dealer lot. They already had rusty manifolds from running and loading on trains and trucks. They were all a light cream/rust color...lol.
Posted By: ScottSmith_Harms
Re: How hot do cast iron exhaust manifolds get? - 12/13/08 05:41 PM
Quote:
No car ever looked that way on the dealer lot.
True, but if you prefer to not see rust it's a heck of allot closer to looking original than ANY kind of paint or high temp coating. Oh yea, and it's practically free!
Posted By: BDW
Re: How hot do cast iron exhaust manifolds get? - 12/13/08 06:02 PM
Scott,
You ever coat them already on the car? I really don't want to pull them off again.
I know you mentioned a light touch up, what about the initial job?
Posted By: ScottSmith_Harms
Re: How hot do cast iron exhaust manifolds get? - 12/13/08 06:18 PM
No, won't work well, you need to remove them, blast them, and then coat them if you want good results. Just slopping some on already half baked /rusty manifolds will usually result in a blotchy weird looking finish.
Posted By: mopars4ever
Re: How hot do cast iron exhaust manifolds get? - 12/13/08 06:26 PM
I was told to try mineral spirits and graphite by a older man at a car show I was attending a few years ago. I bead blasted the manifolds and rubbed it on. It is messy but they have stayed nice looking so far.