Well i'm trying to decide whether I should run Mobil 1 in my 3.4 with 81,000 miles or just stick with conventional oil. I'm just worried about the possibility of Mobil 1 causing a leak. I know my truck has run Amsoil in the past because there is a sticker on the dipstick that says "Amsoil synthetic motor oil do not add or replace without owners permission", but not sure how long it was used for. When I just had my timing belt/waterpump replaced at the dealer they said my front crank seal was "seeping oil" and replaced it. I know most of you run synthetics, so am I going to have any problems with Mobil 1 getting past any seals/gaskets in my engine causing leaks?

 

chances are if their is no problem or leaks now then it will be fine..... however if there are current leaks... then its going to leak worse.....

 

I switched both my Runners over to Mobile 1 syn and both were just over 88k and no leaks with mine.

 

Mobil1 is the best oil I have ever used...I switched at around 60K with no problems

 

I just switched to Royal Purple at about 135K miles. Purrs like a kitten.

 

I switched to castrol syntec at 88k and it leaked like a siv when the engine was pushed hard. I switched back to conventional oil and everything is fine now.

 

Was your PCV valve ever replaced?

 

Yes. The majority of the leaking came from the rear main seal.

 

Oh, it seems like the 3.4's are not as prone to leaking with synthetic for some reason. It's good to know your leak stopped after switching back to conventional.

 

I switched my 3.4 to amsoil at um...177k miles! No leakies.

 

It seems like most of you guys waited until you had a good amount of miles on your engines before you switched. I've heard that I should wait until 50K or so before running synthetic. Is that true? If not, when can I switch? Is it alright to switch at the first oil change (5K miles)?

 

Yep, it's fine to switch right away.

I got mine at 153k soooo..........

 

I switched to Mobil 1 synthetic at 90k miles on my truck. I have no leaks. I had no leaks with dino oil either but if there was a slightly bad seal somewhere the synthetic would have exposed it.

 

a "sieve" is like the thing you pour your spaghetti in to drain the water, like a colander, hence leaky

sorry, it's the English teacher in me

 

Chickenlover: Quick question. Are you the original owner and was the oil changed regularly before switching to synthetic? Just trying to figure out why some have leaking problems.