Cracked Exhaust Manifold symptoms

[loganss]

Ok Can some one tell me what a slight crack in your exhaust manifold can do to your car?

[davens]

Ok Can some one tell me what a slight crack in your exhaust manifold can do to your car?

What can it do?
Well, sound like ass.
You'll fail inspection where I live.
Puts exhaust carbon/soot in strange places.
I "think" it can contribute to EGR problems.

I'm on my third manifold. First time I attributed it to bad luck...it happens. Second time, I was pissed but maybe it was because I used an exact OEM version of the first. As near as I can figure, the pre-cat was clogged enough that excessive heat was building in the manifold...splash some water from a puddle or rain on it while driving and it could crack.
But it's been between the 2/3 primaries which leads me to bleieve it's a stress point. So I dumped the pre-cat and slotted the mounting holes so manifold can flex/expand /contract a little better.

I've read of a few other people having the same problem...it's not a TSB, recall or anything asfaik. There regularly is a replacement on Ebay. This tells me there's a need. It's supposed to be better iron alloy(more nickel?) and there are some structural reinforcements added.

If this new one cracks, I'm driving the car into the quarry and claiming the insurance. There's just no excuse. I mentioned it to the Mazda service department and they had nothing to offer.

[Distractedfrog]

ok so what are some of the symptoms?

[davens]

uh...a big old crack right across the manifold.

You might need to remove the exhaust shield to see it, which can be a hassle in itself.

[loganss]

ok so what are some of the symptoms?

Davens listed some possible symptoms in his first post.

In another thread that I posted in, Naomi mentioned the following about error code P0421 - Warm up Catalyst Below Threshold:

Check your manifold. 421 usually means an exhaust leak. Pull off the manifold shield and see if its cracking between 2nd and 3rd cylinder outlets along the manifold. This is a very common stress point. If its cracked, buy a new manifold off ebay for 50 bucks, get it powder coated (or ceramic coated) for another few bucks and it probably will never crack again since its now protected from a lot of the heat produced by the engine.

I got one of the manifolds from ebay, but it got ship to my NJ address and I'm in MD. It's going to be a while before I replace it. I'll be sure to post when I do though.

[loganss]

When I took my manifold sheild of and I searched through some of the rust on it I saw a hairline crack. It wasn't a big gaping hole or anything. I just don't want it to turn into on that's why I'm wondering what kinda damage it can do to my car.

[davens]

If its cracked, buy a new manifold off ebay for 50 bucks, get it powder coated (or ceramic coated) for another few bucks and it probably will never crack again since its now protected from a lot of the heat produced by the engine.

Correct me if I'm wrong, but isn't the manifold the biggest producer of heat in the engine bay?
If you're going to get it coated, careful what kind of powdercoat...the regular stuff will not hold up to that level of heat. There are special hi-temp powders for this kind of thing. Ceramic would be better but it's expensive.

[frankh]

tHOUGHT i WOULD OFFER SOMETHING

When my Wife came into my life complete with Protege we quickly noted the increasing exhaust noise and the soot from behind the heat shield on the downpipe.

i took the downpie off and found two cracks one on each side,,,I thought this was trange and as the pipe was in otherwise good shape I gas welded it up and reinstalled the downpipe.

The fact it cracked in the first place bugged me and the more I thought about it the only reason the pipe would crack is if it was expanding due to heat and thus, getting longer. If the increased length had nowhere to go it would bend the pipe at the bend where it curves backwards under the engine.

Bingo...The stupid a**es had put a bracket on the engine block UPSTREAM of the flex joint. Thus the pipe is bolted solidly at the manifold and under the engine.

No wonder it breaks and the stresses on the manifold must be huge.

So I dropped the clamp off under the engine and thre it in the trash...No more cracks in 7 years!

This is probably old news but I thought as a newbie I would post my experience in case anyone wonders why they get cracks in the exh downpipe and/or manifold.

Cheers

Frank

[frankh]

OK so our car is a 94

and therefore the above post is in the wrong place, but hey it mifght still be useful...I'll repost the above in the 1st Gen forum.

Frank

[soldierboy15]

And if I am not mistaken a cracked exhaust manifold can lead to the destruction of your catalytic convert. This just happened to me.

My check engine light came on and it pointed to the cat. After further inspection I found that my manifold was cracked. So now I am in the process of replacing both of them.

[frankh]

I wonder

If your cat is perfectly but the oxygen intake thru the crack might be throwing off your O2 sensor, if indeed you have a code for it or other symptoms.

Can you not simply weld up the crack (and find out why it cracked in the first place) and see what happens?

Would be a lot cheaper at the risk of a bit more work potentially.

Frank