The Stovebolt Site Forums The Shop Area General Truck Talk Exhaust smell in cab??

I searched the forum and did not find anything discussing a potential link between exhaust smell in the cab and the cowl vent drain line. As I was plugging several holes on the firewall in an effort to minimize the strong exhaust smell I looked at the cowl vent drain line that ends right above the voice cover as a potential cause. It appears that there could be a venturi effect going on as the air flows through the vent into the cab sucking fumes as it flows past the drain. I plugged the drain with a bolt and waiting for the rain to stop to test this theory.

Has anyone rerouted or plugged the cowl drain due to similar problems or I am missing something?

BTW, the exhaust pipes run all the back past the back bumper.

" . . voice cover . . . " ? - fumes from the slits/openings (exhaust smells?)?

We knew what you meant:
valve cover

Clutching at straws:

#1: Is your road draft tube clear?

#2: Get a nylon tubing connector and a 4' length of rubber vent hose. Extent the vent hose to exit under the starter. I do this to allow rainwater from the vent to exit under the truck, rather than over the open-slitted valve cover (1955-1st and earlier). That hose-extension should also result in air being sucked out the hose under the truck, when moving.

I will try that once I confirm that was the source of the exhaust stank . Thanks. Kcd

If the exhaust leak is so bad that it is getting sucked through the drain pipe, then you either have a sizable exhaust leak at the head, exhaust pipe/manifold, or a huge gap around the intake pre-heating box.

X2 on what Carl said, If you are getting that much smell in the cab you either have a large leak in the engine compartment or under the cab. The other possibility is that its not exhaust but oil burning off from a valve cover leak or something of the like. Extending the drain tube is not a bad idea but you really should figure out where the smell is coming from, fumes of any sort in the cab ain't all that healthy.

My temp plug seemed to work. I hear what you guys are saying about the leaks but the source really isn't all that obvious. The hunt continues for now.

The older I get the more sensitive I seem to get to fumes of all types ( like raw fuel, exhaust and crankcase).............

I agree the drain tube can allow fumes to enter the cab. Especially if the engine has some blow-by and the tube is inches away from the valve cover slits. I sealed my vent drain tube witha gravity seal that opens when water is present. My engine has a PCV, rebuilt but still sealed all possible areas of entrance of fumes.

Seal all the holes on the fire wall. Hood to cowl seal is direct path to the cowl vent area.

Raw fuel smells are also common and rich mixture makes for strong exhaust fumes compared to modern vehicle. Hot fuel percolation and open float bowl vent makes for raw fuel fumes.

Play with the venting and windows as a experiment to vary the cab pressure. Creating a negative pressure in the cab invites the engine fumes is through the smallest cracks and holes.

Worn heat riser shaft bushings is a common exhaust leak point.

The road draft is totally ineffective at speeds below 25-30mph. Add a PCV is a large improvement on controlling engine crankcase fumes.

Thanks, kcd

there may be a more serious problem, but old vehicles have a lot of smells you don't get with modern cars. maybe?

It is much better in the cab with the drain line plugged. There is no visible exhaust leaks. I can live with this for now as the engine will probably be rebuilt in the next couple of years. Kcd

I fixed an exhaust manifold leak - that along with plugging firewall leaks seemed to work.
Lots of blowby does have a way of getting in; pcv may help.