My 92 LS400 started up perfectly fine before this weekend where temperatures were minus 10 in Ottawa for the first time this season.

I would turn the key and nothing at all. Lights were still working but would slowly dim. Id boost the car and it would start right away. Drove it for about 30min and parked it last night. Did a test start and it started. This morning again minus 10 and the car wont turn over at all.

Is it just a weak battery? or something else?

 

cold be weak battery, bad battery connections (the positive terminal ends go bad on LS400, about $15 at any Toyota dealership) or bad ground or a current drain (such as a small unnoticed light staying on, etc.)

take a reading with a multimeter next time it won't start, you should have 12.6V with car off if battery is good, and you can hook your meter in series with the battery to see how much power is being drawn off when car is off (a tiny amount is normal)

also, using a full synthetic 0W-30 will make it easier to start in cold weather and will extend the life of the engine, by getting oil to critical parts faster.

 

When I first got my 99 ls400 about a year ago I had problems getting the car to "fire up" when temps fell below about 15 degrees F. I believe the previous owner did not put many miles on the car in the months leading up to my purchase.The car may have had some buildup in the fuel system. Anyway,a couple tanks of fresh premium gas with Techron fuel treatment seemed to clear up this problem for me. Anybody experience a similar problem with cold weather starting? When I purchased this car it ran perfectly until the cold weather arrived.

 

also the cold weather can bring to the forefront problems that were masked with the higher heat, such as a broken wire, idle air control valve, etc.