Used car -- unknown maintenance history

[ITgears239]

I bought a used 3000GT with 140k miles on it. The engine does not smoke or consume the conventional oil that is in it.

Should I swap to synthetic? Would it be better to run Auto-RX through it for the next two oil changes with conventional then swap to synthetic? I know Auto-RX won't fix any leaky seals if they are ripped under the carbon deposits but is it a good idea or just leave it be?

Would it be better to just stick with conventional and/or use Auto-RX at this point?

I'll be replacing the valve cover gaskets next week so I'll get a better view at how clean the motor is. None of the seals besides the valve cover gaskets leak and even that is a very very small amount (just enough to stain the valve covers over time but not enough that I have to add oil).

I should also say, in the 4 years that it was owned only about 9k miles were put on it. So it sat a lot but it drives great.

 

[MolaKule]

Quote:
Would it be better to run Auto-RX through it for the next two oil changes with conventional [oi], then swap to synthetic?


I would recommend this route since it woold be a gentle cleaning. Change filters at 1/4 to 1/2 normal OCI.


Also change the PS, transmission and diffy fluids since you don't know if those fluids have ever been changed.

 

[Billbert]

And flush the brake fluid. Nice car!

 

[Bottom_Feeder]

Why would you want to start putting synthetic in it at this point in the car's life? If it 'likes' what is in there already, keep doing it.

 

[ITgears239]

Originally Posted By: MolaKule
Quote:
Would it be better to run Auto-RX through it for the next two oil changes with conventional [oi], then swap to synthetic?


I would recommend this route since it woold be a gentle cleaning. Change filters at 1/4 to 1/2 normal OCI.


Also change the PS, transmission and diffy fluids since you don't know if those fluids have ever been changed.



So you don't think 140k on a 1993 car is too old to make the swap with the help of Auto RX?

I already changed the other fluids (besides the break fluid). I'm just nervous about swapping to synthetic and keep going back and forth.


Originally Posted By: Billbert

And flush the brake fluid. Nice car!



Thanks, I like it so far but mostly just fixing it up and driving it to work for now. Good point, I forgot about the brake fluid.


Originally Posted By: Bottom_Feeder

Why would you want to start putting synthetic in it at this point in the car's life? If it 'likes' what is in there already, keep doing it.



That's exactly why I keep going back and forth. Do you think Auto RX would be a bad idea at this point too?

If this car was newer I wouldn't give the miles a second thought to swap to synthetic but at almost 20 years old... it really makes me wonder.


Thanks for all the responses.