Oil consumption and noticeable MPG loss

Hey folks, a few months ago I switched to synthetic Mobil 1 in a 1999 year old taco that most likely never had it. I have 2600 miles on this synthetic and noticed I wasn’t getting near my 270 miles on one tank (got 220). Checked oil and it was on the low mark which has never happened before. Checked for leaks and found none. Checked out the exhaust and it was slightly smoky (light gray/blueish color). So obviously the engine is burning oil and I’m wondering if I should buy the complete engine gasket kit or could I focus on just a few gaskets to seal off the leak to the engine ? I already have the valve cover kit. Thanks...sigh...

 

Is it only smoky on start up after it's sit for a bit, or is it smoky all the time? Rings are probably warn if it's smoky all the time.

 

i will report back on that. This is all new to me.

 

Something else to keep in mind is that switching to synthetic can give you problems. Synth is thinner, so it has a tendency to "find" oil leaks. It's a myth that you can't switch back, so I would honestly switch back to conventional oil and see if your oil consumption goes back to normal (zero).

As the below link says, "the best oil for your vehicle is the one the manufacturer recommends." This usually differs from the "best" oil that an oil manufacturer recommends.

https://blog.firestonecompleteautocare.com/oil-change/should-you-switch-to-synthetic-oil/

 

Switching back might not change the leak since the synthetic probably cleaned it up real good in there and removed sludge build up.

 

Meh, that's part of the whole myth of not being able to switch back.

Honestly, the worst that could happen is that you still have the same problem you have now, and your fixes are the same as they would be with synthetic. Best outcome is you find out your motor doesn't have the tighter tolerances that synth requires, but conventional works perfectly fine.

As I said earlier "the best oil is the one the manufacturer recommends."

 

I get that, I could switch back. She’s got just about 300k miles now and wanted to use better stuff. Switching made her quieter and feel better (unless that was my mind playing tricks). Probably needs new seals anyway since they’re very much used. I just don’t know what one would be leaking.

Also, Toyota only recommends 5w-30. I don’t think it talks about using conventional / synthetic.

 

Usually, if it doesn't specify synthetic, that means conventional.

If anything, you'd want a high mileage oil. Synth isn't necessarily better in that respect. Synthetic oil of the same weight is actually a little thinner which is not what a warn out engine needs.

Seals aren't a bad idea, but didn't you say it wasn't leaking, but consuming oil? If it's not leaking, then your seals are likely fine. Might need to just get under there and clean it off real good (engine degreaser, etc...) then top off your oil and see if you can start seeing any signs of leaks.

Obviously the burning oil thing needs to be addressed. Cheapest option is just switching back to conventional as I suggested and just see if that does it. It might, or it might not. But it's cheaper than replacing your rings and pistons, lol...

 

burning oil is going to kill the cat in short order too. hopefully you find a solution.

 

Hmm.
It’s not leaking on the outside (yet) I was referring to it’s leaking from inside the engine to the combustion somehow and burning. I want to fix that. I don’t think switching back to my previous oil will now fix my leak as the engine has been “cleaned” of stuff that was preventing leaks. It’s old and probably overdue. 300k miles is, well, a milestone.
I’ll see if the smoke comes out during start up only and report back. I hope I don’t have to replace anything too expensive.

Also, would this cause MPG drop? It’s very noticeable.

 

A compression test can help to diagnose warn piston rings, bad valves, or other issues, too like a head gasket.

 

I’ll get the compression test posted as soon as I can.
Alright just got home and my cold start took about 10 seconds before smoke started to come out and about 30 seconds to be normal, drove home got out and there’s currently no smoke coming out.

 

Hmm, interesting. With a bad valve seal, there's usually a puff of smoke right at startup, from oil dripping onto the piston, and that gets burned up immediately. Ever see a jet engine start up? It's like that, lol.

I wonder if it could still be the rings, but once it get to operating temperature (expands slightly) it's enough not to leak (as bad).