Hi all, I went to mitsubishi for full service yesterday, after it been done, I took it for a drive and I found that my car proformance not as good as before and the lifter getting lounder, I use the GTX 15w40 oil, before that I used the 5w30, is that ture that I can't use 15w after I been using the 5w30? Its an Evo 5...What should I do?

 

Why 15-w40 ???

 

I took it to mitsubishi dealer, they changed it for me, is it bad for engine?

 

It can be.
Drain it and put lighter oil in. Heavy/high vis oil like that will likely cause high pressure and beat on your everything. Take it back and complain. I would not go WOT with that stuff in there though.

 

I recently switched from 10w-40 to 20w-50 and only noticed the car is a bit quieter at idle.

 

So are you saying 15w40 is bad for my engine? Should I take it back and ask for refund?

 

For a stock engine I would only use 5w30 and 10w30. 15w40 might not give you proper lubrication on a stock engine.

 

those dealership kids are jokes