Hi guys. I hope this question haven't be asked before.
Would like to find out whether these caps are the same? Because in Mazdatrix have S4 & S5 FC3S cap and I bought S5 gas cap for the year 91-92.

http://www.mazdatrix.com/n-6.htm

My car is a S4 year 1986 with S5 Engine (not sure the exact year). I doubt the previous owner replace the gas tank and piping to S5. I just bought the S5 gap cap, so would there be any problem if I'm not using the exact specification gas cap for my car??..........

 

If he replaced the whole thing then hopefully he replaced the neck/nozzle. If not you might have to get the other one.

 

thanks...

any idea how to check whether it is a s4 or s5 tank and neck? I've asked my mechanic, and he is not sure and told me both are the same...

 

Look at picture differences?

 

I'm pretty sure the caps are interchangeable, unless '86-87 S4s are different from '88s. The cap on my '88 GTU is the same as the cap on my '90 GTU was. When I bought the '88, the OEM cap had been replaced by the previous owner with some kind of universal crap one that was cracked to boot so I ordered a new one from Ray Crowe at Malloy Mazda. It was the same color, shape, size, etc. as the one on my S5. Granted I did not actually try to exchange them so I guess it is possible the thread pitch could be different, but I'd be really surprised.

 

Thanks.
Taking about color. Are series 5 cap color is orange in color and series 4 is dark grey?

 

they are interchangable.. I bought one for my S5 vert and removed it and put it on my s4 coupe later when I sold the vert...

 

I owned my S5 almost since brand new (bought with 8000 miles in 1995) and it came with a mustard yellow cap with white printing on it. I forget what it said, probably "Unleaded Fuel Only." The cap I bought from Malloy Mazda last year for my S4 was the same mustard yellow color but no longer has the printing on it. Since I bought my '88 with an obvious replacement cap, I can't say what the original color for S4 would have been. Are you trying to do an accurate restoration?

 

Yup. Since Mazdatrix has stated 2 different gas cap for year 86 to 90 and year 91 to 92. I'm affraid there might be a fuel pressure differences or something like that and it may damage certain things when times goes by if I did not use the correct specification. I don't know. Maybe I'm being paranoid. Since my car is S4 with S5 engine and no one can tell whether my fuel tank and neck has been replaced to S5 as well.

 

Well, the mustard colored S5-style cap is what Ray Crowe at Malloy Mazda sold me for my S4 car. I'm guessing it's all that Mazda carries anymore. It fits perfectly and I've been using it now for over a year with no negative consequences, no Check Engine lights, and the car easily passed its emissions test. I can't think of any reason to worry about it.

The kind of weird thing about the Mazdatrix listing is that they specify one part number for 1986-1990 which would include all of Series 4 and the first two years of Series 5. Was there some kind of change to the fuel filler neck in 1991? The other interesting thing is that the photo on the web page link you posted shows an obvious SA/FB gas cap and a gray S4/S5 cap but nothing in the mustard color. You could always give Mazdatrix a call and see if they could tell you the difference between the two caps they sell. I guess if you're set on keeping the car as original as possible and the S4 cap was in fact a different color, you might want to order the gray S4 cap if any are still available.

 

Thanks for your advice David. I did contacted Mazdatrix regarding this matter. All they can say is that, find out which gas tank I'm using and use the correct specification gas cap. Anyway, since there has been replies saying the gas cap are interchangable and you have been using the mustard colored cap without any problems, which is the same one I bought from Mazdatrix, I guess I just stick with it. I know it shouldn't be any problem and its interchangable. Just that I worried too much about it.