i have replaced two starter in one week

Yes, you have the wrong starter. It has to be for a Cummins engine, the Cummings engines use different starters. Call Volvo and ask for the part numbers and see if they are different. Make sure you tell them you have a Cummings engine so they don't confuse it for the Cummins. Classic mistake.

 

I see what you did there...

 

Low voltage will cause a starter to hang in after the engine is running without you realizing the starter is still running and grinding against the ring gear teeth. Check/test your batteries, all wiring/connections and your ground straps.

 

First thing to check is the grounds, always check the grounds, they will produce some strange symptoms. Also double check that your wires to the solenoid are not touching other posts, I have seen where they are close and when it gets hot it will contact one of the other posts on the solenoid and cause the starter to engage.

 

just replaced starter because of bad battery voltage, one battery was bad.

 

Did that solve your problem???