user91640: I just found my "old" wallet.dat.
Is it possible to "send" it to an online-wallet in order to avoid downloading the whole blockchain again?
Or can I do it directly because I have the Address and ID of the coins?

user63872: 
I just found my "old" wallet.dat. Is it possible to "send" it to an online-wallet in order to avoid downloading the whole blockchain again?

NO. In fact, any service that asks you to transmit your wallet.dat file is most certainly a scam. 
A wallet.dat file contains a collection of private keys, which are what is required to spend your bitcoins. So if you would like to use a different wallet without syncing the blockchain again, then you will need to dump the private keys out of your current wallet, and find a wallet that lets you import (sweep) private keys into it. 
You can use a light-wallet to do this, rather than trust an online-wallet. You may be interested to check out the list of wallets on bitcoin.org, but remember to do your own research to ensure that you are downloading reputable software from a reliable source. 

91640: <p>I just found my "old" wallet.dat.
Is it possible to "send" it to an online-wallet in order to avoid downloading the whole blockchain again?
Or can I do it directly because I have the Address and ID of the coins?</p>
 63872: <blockquote>
  <p>I just found my "old" wallet.dat. Is it possible to "send" it to an online-wallet in order to avoid downloading the whole blockchain again?</p>
</blockquote>

<p>NO. In fact, any service that asks you to transmit your wallet.dat file is most certainly a scam. </p>

<p>A wallet.dat file contains a collection of private keys, which are what is required to spend your bitcoins. So if you would like to use a different wallet without syncing the blockchain again, then you will need to dump the private keys out of your current wallet, and find a wallet that lets you import (sweep) private keys into it. </p>

<p>You can use a light-wallet to do this, rather than trust an online-wallet. You may be interested to check out the <a href="https://bitcoin.org/en/choose-your-wallet" rel="nofollow noreferrer">list of wallets on bitcoin.org</a>, but remember to do your own research to ensure that you are downloading reputable software from a reliable source. </p>
