I hate to start this thread, i know its been covered alot. I think i have a manifold crack. With the hood open i can clearly hear what sounds like a muffler around the exhaust manifold coming out of the engine bay, and my mpg has been going down these past few tanks.

Does this sound like a crack manifold?

Thanks so much,
Chris

 

Could be an exhaust gasket too. Feel around for exhaust gas escaping while its running, just (obviously) be careful not to touch the manifold or exhaust pipe. You'll know if you have a leak.

 

It could be that it is cracked or the gasket is bad like 111db suggested. It is a fairly common problem on the 2.7. I would unscrew the 4 bolts that attach the heat shield so you can examine the manifold carefully for hair line cracks.

 

thanks guys, at lunch tomorrow i am going to remove my heat shield and see if i can see anything.

 

its worth a look even if you dont think its cracked. I took off my heat shield to clean out some mud in my engine bay and BAM! there was about a 3" crack down it that looked like when the manifold was hot and expanded it sealed itself but I didnt want to take any chances so I replaced it

 

Take a couple feet of hose, be it garden hose of fuel hose and put one end to your ear, move the other around the exhaust manifold (engine running) until you find the leak. It will sound like a helicopter flying overhead. When I thought I cracked my manifold, it turned out to be a burned exhaust gasket.

 

here is the most simple test.
get a can of seafoam run a little through the stuff sock in the end of the tail pipe then quickly check over the exhaust pipe or if you have a helper have them hold a wet towel over the tail pipe end that has been folded up a few times so they won't get burned.

 

If it is cracked or leaking, how bad is it to drive around on it until i can get headers?

 

Yo man, I've been down this road with my manifold and it does suck. However, it is a good excuse to get headers, I just opted for an OEM because I didn't have the cash at the time for the $400 header from LC. I do regret this now but at the time I didn't want to drive around with the crack. I'd say I drove it at least a month after I noticed the crack and maybe longer because who knows how long the crack had been there prior to me noticing.

Do what you gotta do, but I'd say don't wait 2-3 months before getting it fixed. If you don't have the cash opt for the $70-80 replacement.

As for the install its not bad at all, takes some time and you'll need a good breaker bar to get the bolts off the engine block but its pretty plug and play. I would suggest getting some extra studs and bolts from the dealer as one of mine broke during install, but I had thought this might happen in advance of doing the job so I had some.

Let me know if you have some questions...like I said its not terrible to wait but get'r done as soon as you can.

 

A cracked manifold will not destroy anything, you can run it forever that way as long as the leak is not heating any hoses, it will be louder and it may smell in the cab as the exhaust is coming from in front, but if you need to save some cash up to get a new part then its cool to drive around. i have seen the dyno numbers from cars tested with and with out any exhaust, the one with out was much higher, and the common "back pressure" is not proven any where I know many of you wont believe me but hey to each his own and until i see dyno numbers that disprove what I have actually seen, then I don't believe the stereo shop that says it feels faster with the "right size exhaust"...

 

I found the leak on my 2.7 using seafoam. I didn't have to cover anything up, because the seafoam started smoking pretty good from the crack.

I waited about 2-3 weeks before i replaced it with an OEM manifold. Funny thing is, the parts guy at the 'yota dealership said it wasn't that common... Guess he doesn't go online too much.

 

This is 100% NOT TRUE. I got this advice when my manifold cracked and ran it for a while figuring I would save up for a new one...after a while I was noticing horrible gas mileage and loss of power. I eventually got a check engine light. I ended up with a couple burnt valves which caused low compression in those cylinders. It was expensive to get it all fixed and was directly attributed to the cracked manifold. I would say that if you have a crack, it wouldn't be bad to run it for a short time, but I would not run it any longer than absolutely necessary, you are risking your engine by doing so.

 

I have been noticing a little power loss lately and gas mileage is going down.

Guess what shined its little head at me, this baby.

 

Oh, and got a leed on a new LCE header, and getting new studs.

going to have to take it to an exhaust shop to have the cat and stuff kind of reworked to fit the header.

 

my crack is about twice as big as yours

 

should this be fine for driving to work for a week, (40 miles a day)? i dont want to screw anything more up, and i dont know how long its been cracked, just recently it has been getting worse mpg and lower power, these symptoms happened after a 1200 mile trip.

 

will a manifold for a 2000+ 2.7 fit on my runner?

 

hahahaha, sorry - couldnt resist.

 

Can an exhaust manifold crack show up as stumbling or hesitation even though I can't hear the problem under the hood? I have a 1997 4Runner with the 3.4L that is missing on takeoff (sometimes). I've replaced both O2 sensors, the TPS, cleaned the MAF, changed spark plugs and spark plug wires, then Seafoamed the engine. I'm thinking about of taking it to the dealer for diagnostic but wondered if a cracked exhaust may be my problem.

 

X10 --- my dumbazz friend thought the same thing (that it wouldnt hurt) on his old school blazer and about 6 months later he developed valve issues and need the upper half of his motor rebuilt.. why take the chance? it isnt too expensive to get it fixed


btw do they have this issue with the 3.4's? out of curiosity