Exhaust Fumes - International Scout - 1973

Got a 1973 International Scout II with 304 V8 (original motor). Exhaust system is fine but old. I am gonna replace it this winter. My question is this…If I replace the exhaust system from the manifold back should that alone solve the issue of the vehicle smelling like exhaust fumes? I know that maufacturers began to faze out the use of leaded gasoline engines in the early 70’s and heard that changing something on the intake or fuel system will allow the engine to run more efficiently on unleaded gas and solve the fume issue. I cant remember what the part was they changed out. It was on the TV show “Wheeler Dealers” which is a British show that is aired on the Velocity channel. I assume the same reasoning would apply to American made vehicles but I am not sure and can’t find out if this engine was able to run on leaded fuel in the first place.

The change involved replacing the valve seats with hardened seats, but I think a '73 would have those. You can check if it’s a problem by doing a compression test. Low compression could be caused by ‘burned’ exhaust valves. Also by worn rings. If you have low compression a leak down test (or a squirt of oil and a repeat test) would tell you which one.

But smelling exaust fumes is more likely caused by a leaking exhaust system, so replacing it should solve that problem. You should also look for rust holes in the body that are letting those fumes in, and repair them, too.

I have been chasing this type question for a long time in my Olds. The exhaust smell is different on pre-catalytic converter cars and I firmly believe is one problem. The second involves sealing up the body so fumes cannot be pulled into the cabin of the vehicle at speed because of the low pressure area at the back of the car that basically holds the fumes there at the back. Crack open a window and you create a draw from the back of the car to that open window, basically sucking in any fumes hiding at the back of the vehicle waiting to come in.
Yes fix the exhaust leaks for sure, it can only help. Then look for any area on the vehicle that may have holes that could allow fumes into the Scout and cover with new seam sealer. Check all old sealer for cracks because that will allow some smell to seep in too. Check the seals on the back of the Scout window and door back there and make sure the seals are good.
But in all this, just remember that old car exhaust doesn’t compare to the new car stuff. Everyone I talk with and know says the older cars will have some smell. The use of catalytic converters and better fuel monitoring with oxygen sensors has really cleaned up what we smell on a daily basis.

If the tailgate weather stripping is not sealing properly exhaust will be pulled in through the gaps at speeds above 45 mph. Your exhaust may be OK.

The 73 Scout has hardened valve seats. My Grandfather had one as did a few friends had them as well. They could be run on both unleaded and leaded gas. Grandad was real old school. We had hard time trying to get him to stop adding lead additive to it when he no longer could get leaded gas. Check that floor for leaks and a new exhaust you should be good to go.

Thank for all the info everyone. As far as holes in the floor…it’s got plenty but I am working on them one by one…there not to bad for an all original body. I hoped to get the answer you all gave me. Gonna come back here for more advice in the future! Thanks again - Brannon

If the back window gaskets are bad then you’ll pull exhaust fumes in via the tailgate and back window. The Scout body was never very airtight to begin with and at this age my guess is a lot of exhausty air is being pulled back in from the rear of the car. A new exhaust system may help, but if the current exhaust isn’t leaking the new one won’t make that big a difference.

If you do end up replacing the exhaust system, use some exhaust sealant at the joints, it might help a bit.

But definitely check out the tailgate seals. A $1 bill works well for that (see if the seal holds it in place).

What you might do is put this on a tread mill dynamometer and have the exhaust gases analyzed. I don’t remember off hand which carburator was on this engine. If it is a Holly or another with a power valve, you might be running rich which makes that exhaust quite obnoxious. The carb may need a rebuild or rejetted to a leaner condition. Maybe cleaning up the exhaust will cure your problem.

IIRC the IH Scout was an open cab utility vehicle (like a jeep) maybe with a winter cap. Trying to seal all of this up is going to be difficult. The flat rear is tailor made to trap exhaust gases behind the vehicle. Any vacuum leak produced at the sides will draw the exhaust forward.

The emissions from modern cars are now so low that you notice how really poluting early engines were. Every now and then I catch a whiff of a VW Beatle. I can smell raw gasoline, rich exhaust, and burning oil. Ahh, the scent of old engine in the morning.

If exhaust work is done, moving the tail pipe to just ahead of one of the rear wheels and extending out beyond the tire an inch or two might reduce the likelihood that the exhaust finds its way into the cab.

You can stuff a rag in the tailpipe with the engine idling and you will hear any leaks hissing. The exhaust system should be tight enough to build up a little pressure…It should be difficult to keep the rag in place…Also, the point at which the tailpipe exits is important. Manufactures spend a lot of time looking for a spot where the fumes don’t get sucked back up against the body…If someone has changed the exhaust outlet location, move it back where it belongs…

Right up by the manifold to exhaust-pipe joint you may find a “heat riser valve” usually on the right side but not always. These are prone to get loose and leak. A leak at this point will find its way into the cabin…

@Reseacher , the rich theory is a good one but also lean conditions can cause some obnoxious smells. Either direction can be looked at on a dyno.

Here’s a photo of one (I haven’t seen one in a LONG time):

Scout II with the later body style…