My Lexus GX470 is currently showing a cylinder 1 misfire error, but only during engine startup. I have already replaced the spark plugs and the ignition coil, however the problem still remains.

There is also another issue: the coolant/antifreeze level keeps dropping and needs to be topped up regularly — approximately 0.5 to 1 liter per week.

I was told that the left cylinder head may be cracked and needs to be replaced. According to the diagnosis, coolant from the cooling system may be leaking into the combustion chamber. As a result, when the engine is still cold, the air-fuel mixture in cylinder 1 does not ignite properly, even if the ignition system is producing a spark.

I would like to know whether anyone has experienced a similar problem with the GX470, and what the actual solution was.

 

Loss of coolant with a misfire is normally pretty serious.
I would pull the spark plug and use a camera to see if there's any scoring on the cylinder walls, and whether the top of the piston is being washed clean.
Also do a cooling system pressure test.

Chip H.

 

What year and how many miles, please....

 

You could check the oil for signs of coolant (inside the oil fill cap often gets white crud built up if this is the case), and do a compression and leakdown test on the suspect cylinder.

Coolant doesn't just disappear, so if you don't have an external leak, you likely have an internal leak, and I would treat that as very serious, in need of attention. .5-1L/week is a serious leak.