Does having a cracked manifold decrease your MPG???

[tundraman89]

My manifold is cracked and my MPG has gone down about 5 miles per gallon?

[AllYotas]

yes it will.

[Big_Al1]

Originally Posted by tundraman89

My manifold is cracked and my MPG has gone down about 5 miles per gallon?

Man thats a big drop Probably worth getting headers to fix this problem and also get some performance out of it.

[bbfirebird]

It definitely will. It would slow down your exhaust pulses, screw with O2 sensor readings, etc etc. If your O2 sensors detect the engine running too lean, it might richen the mixture, not only decreasing MPG but overall performance as well.

[willy]

Originally Posted by tundraman89

My manifold is cracked and my MPG has gone down about 5 miles per gallon?

I have an '00 with one cracked exhaust manifold, and it's been cracked since I bought it used 2.5 years ago. When I filled up yesterday I averaged 19 mpg, which is actually the best I've ever had. I ususally get 17.5 or so. Of course my wife was driving it for that entire tank, so that likely helped, but that did include 250 miles at 75mph.

Technically yes, a cracked manifold will interupt your exhaust emissions. But will it do it enough to alter your mileage? Well, that's a question that would have to be answered via a rigorous scientifically based experiement, as any difference would likely be minimal. I doubt anyone answering yes or no to your question has ever done such an experiment.

The question to ask yourself, and this depends on how long you intend to keep the vehicle, is if you paid $500 for new headers, $60 for new gaskets and collector nuts, and $400 for install (if you can't do it yourself), how long would it take you to recoup your costs and come out ahead if it increased your mileage by, say, 1mpg?

BTW - I'm in the same boat. I plan to sell my '00 in about 1-1.5 years, and I just last month bought some original uncracked exhaust manifolds from a TS member for $75, including shipping. Gaskets and collector nuts from Toyota cost me an additional $60, and I can do the install myself. So, for $135 it was worth it to me, and I hope to install them one of these weekends.

[CHINKinatundra]

if you purchase an aftermarket exhaust manifold, they should include any/all gaskets/bolts/nuts/etc that are required to install.

[Mr. Creosote]

Did the first guy mean cracked exhaust manifold or intake manifold?

[hilandfrog]

It was my understanding that an exhaust manifold leek has the possibility of hurting valves or otherwise allowing cold outside air to hit superheated valves
changing the metabolic structure?

Any truth to this?

VR
Repo

[curryjc]

Also consider having CO coming in through the fresh air vent just above between the hood and windsheild.

[tundraman89]

Originally Posted by curryjc

Also consider having CO coming in through the fresh air vent just above between the hood and windsheild.

I meant exhaust manifold i am going to order some flowtech headers in the morring for $400. Cause the man told me that if it got bad enought i could blow a gasket. I am going to talk to my instructer in the morring to see when we can put them on, so i don't have to pay to have them installed.

[Intrepidyota]

Originally Posted by hilandfrog

It was my understanding that an exhaust manifold leek has the possibility of hurting valves or otherwise allowing cold outside air to hit superheated valves
changing the metabolic structure?

Any truth to this?

VR
Repo

This was exactly what happened to my old Tacoma, cracked the exhaust manifold and burned up two valves. Both my o2 sensors went also, but I don't know if that was due to the manifold issue or just the mileage on them.