mushi99999

I have a 1990 chevy silverado the trans takes syncromesh I'm stuck in the middle of nowhere and had to fill it with 75w90 synthetic. It seems really hot but it's 103 degrees out here. My question is. Can I use this fluid or is this the reason it's heating up? I used to work at a oil center and I think thepenzoil rep said something about syncromesh fluid being close to 5w30. PLEASE Help we've stopped at a hotel and there is a wal-mart near by they do not have syncromesh but is there a substitute i could use to get us 250 miles to the next real city.