I have a spare car, for went its snow up here. It use to be my old car I have had it for three to four years now. since I both my Rx8 two years ago I had it park and use it three or four times went it snow, But with gas prices now I start it to used it daily. It was become my daily driver. Now I drive to work only one mile and one mile back, so not much driving. the car is a Hyundai Scoupe Turbo 1994 it has 120,000 miles. It burns oil like a rotary, I put one qt of oil, every three to four month. I have not done an oil change since I both my RX8, because it was park all the times. Here comes the question, Last times I check the oil, the oil cap was fine (three month ago) this month I check the oil, and it was almost low, so I get a qt of oil to put in the engine and the oil cap does not want to come off. I had to get some big pliers, to get it off, and I mean not to losing it, but I had to use it all the way out. I look at the cap and it look OK but it will not go in any more. I had to go buy a new one, and the new one fits OK. I like to figure things out. So the only thing that I can think of, is that the piston ring are so gone that the compression is going in to the valve cover and the heat expanded the oil cap. That wood explain, why every time I but oil in the engine, the oil around the oil cap looks like tan (like coffee with cream) put the oil in the dip tick look OK, very dark put OK. and no it is not mixing oil with coolant. The radiator and the coolant are OK, and the car start like its new, and beside the valve knocking a littler bit and some smoke coming out went I start the car it runs great!!! So what do you guys think it could be the problem that maid the oil cap expand?

 

you need to change the oil every 6 months or 5000 miles - don't wait till you have done 5000 miles because the oil degrades over time - especially when you don't garage the car .
The cap - who knows , maybe you overheated it sometime . More likely , someone tried to screw it down on an angle and stuffed the threads ....

 

Wow......thanks for interpreting that Brettus!

 

I agreed with you on the oil change, am planning on changing it next week, on the cap, I am the only one that have touch the engine since I both the car and the threads are OK, and as for the overheating it, like I said I only drive one mile to work, by the time i get there it almost up to normal operating temperature and 9 hour later I go home, one mile back . If I have to go some place, I park it and use my Rx8!!!

 

yeh well it was an effort, I have too much time on my hands .....

 

English is Anibal's second language.

Anibal, I think Brettus has the most likely explanation. If you screwed the oil filler cap on while the engine was hot, it may have seemed to go on fine, especially if you were in a hurry. As the metal of the oil filler neck cooled, it contracted and squished the threads of the cap. If they are fairly uniformly squished, they may look okay and still be to fat to thread into the filler neck.

 

I know.............that much was obvious, I was just joking. Anyway, I think you guys probably got it right.......expansion and/or contraction is most likely the issue.

 

Thanks Kristopher and yes, now thinking about it the last time I check the oil and put oil in ( three month ago) I did drive to work firth, so the engine was hot!!!