Poor Milelage Update

[PLP6400]

A few months back I posted about my poor milelage. Which was only 16 MPG. A lot of advice was given and I tried some of them and was able to get 18 mpg. In addition to poor milage I was using a quart of oil every 2 to 3 hundred miles and peridically had white smoke from the exhaust. I was just going to give up on the six and go to a V-8.

This past Sunday I changed the oil and started the engine to check for any leaks. While the engine was running I pulled the PCV valve out of the valve cover and put my thumb over the end. Instanly the idle slowed down and the engine died. The PCV valve was new and had the same miles on it as the engine, 2,000 miles. Apparently oil was being draw into the intake manifold at times and not to mention a vacuum leak.

I replaced the PCV valve and yesterday I had to make a 500 mile round trip. I was not trying for milage as I was going from Reno, NV to Livermore, CA. This involved starting out at 5,000 ft. elev. crossing the Sierra Nevadas to an elev. of about 8,000 ft. to almost sea level and back. Also I was in a hurry and stayed in the fast lanes on the California freeways, which was never under 75 mph and sometimes 85 mph. I travel during non traffic hours when I go to California.

The engine performed perfect, never had to shift out of overdrive on the grades and the best part was I averaged 23 mpg. I still find it hard to believe that a bad PCV valve caused so many problems and cost me 5 miles to the gallon. So I am going to stay with the six and maybe go with a six on my next project, a 63 Falcon Convertible.

 

[Anonymous]

Great find. I may replace mine just as a matter of fact now. They are only a couple of bucks.

r/
Steve-O

 

[CoupeBoy]

a 63 convert, do you have a power top or not? I hope to get Dad's 63.5 drug out next summer. He has had that car for as long as I can remember and I have never heard it run or seen it move under its own power (but it did tail gate us for 1500 miles from Portland OR, to Jamestown ND)

Glad to hear the six is running better.

-ron

 

[PLP6400]

Hi Ron
My 63 Falcon convertible does have the power top. It is an early 63 Futura. I traded a rebuildable 289 V-8 and a couple of C-4 transmissions for it. There is hardly any rust on the car, just a few spots on the floor, not enough to replace the floor boards though. I still haven't decided how I want to do this car. I have the complete 170 six cylinder engine, drive train, and brakes from my sons Ranchero that only has 14,000 miles on it. I am probably just going to sell this car after it is finished, because the car I really want to do is my 65 Comet Cyclone.

Patrick

 

[Anonymous]

I might be way off on this but I don't think so. Isn't that EXACTLY what a PCV (Positive Crankcase Ventilation) valve is supposed to do? Don't you test to see if you have a bad one by blocking it and noticing engine response? Usually, if there is no response that's bad and if there is response that's good.

How does the engine respond when you block the new PCV valve with your thumb?

-Dan in Atlanta

 

[mustang6]

Yes, PCV valves are just controlled vacuum leaks. They are supposed to be closed at low vacuum levels (like at idle), so an engine should have trouble idling when they are stuck open at low speeds and run better when you plug them with your thumb because they are supposed to be closed at that speed.

However, if someone has unknowingly forced the engine to run with a bad PCV valve by adjusting the carb all out of whack (essentially covering the vacuum leak by really richening the mixture), then you will see the results that PLP6400 saw- very poor mileage and plugging the valve (extra air source) with your thumb will throw the mixture way to the rich side and kill the engine. Of course, when you put a new PCV valve on, you would be forced to re-adjust the idle mixture to get it to run.

And in the end, he got the A/F mixture right again and his mileage increased greatly... If my theory is true, that's what happened.