Dom that's actually only half correct. I run 15/40 in mine and she starts fine even now. Owners manual states. "SAE 10w-30 preferred". Note it does recommend 5-30 for below -18. But 3° should not make that much of a difference. Moe, he is correct in saying you have other issues and you should diagnose those as well. If you are burning 4l of oil you have MAJOR issues. Most likely rings or a major issue with your valves. It is time to pick up a compression tester. I'd lend you mine but its in storage with the rest of my tools.
PS if your o2 is bad change it you'll get your money back in gas milage.
Also if you are needing to jump your jeep. Then you have a problem with your charging system. Check your battery and alternator. That has nothing to do with oil viscosity. When oil gets cold it gets thicker and the engine will turn over slower. Not... not turnover.
Also has your oil burning slowed with the thicker oil. I'd rather live with a slower turning starter/using block heater, than pay for an engine
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There is something major going on, I have parked the jeep
its smoking a lot and I mean a lot the engine is sluggish and I lost almost half a tank of gas just coming home from work last night.
The smoking coming from the muffler smells like unburnt gas its white smoke not blue or any other color , when in idle the muffler puffs smoke its not constant, I got also when I came to drive it I had to over rev a bit for the engine to run better, then I got a check engine light I plugged in the reader and it said the TPS p0121 or something code I cleared it and it didn't come back again.
Came to a store light and the engine was struggling to keep rpms up.
All this problems just happened yesterday after I cold started it, iv had the oil in there for over a week now, it is thick oil, and takes a bit to circulate my check gages came on just for a split second when I started it yesterday, then I drove it around the block at a slow pace tell it warmed up fully that's when I noticed the smoke and stuff