2001 Land rover discovery with 155k Miles. plugs and wires done 20k-25k Miles ago Car was misfiring so we took it to a mechanic. Diagnosed that cylinder 1 and 6 were the cause so they determined that the coil pack crapped out. We replaced both Coil packs and that seemed to solve the misfires until now(this was less than 500Miles ago). At idle the car is completely smooth running perfect but under half throttle acceleration car starts to misfire. SES light never starts flashing. ultragauge shows pending codes: p0300 p0301 I cleared the codes hoping they would not come back. They did not come back This was about 2-3 days ago. Today i start to drive the disco and it was running very well until i had to accelerate at about half throttle. The disco was misfiring but still no SES. I let off the trottle a bit to about 25% and A couple of seconds later The ultragauge beeped saying there was the following pending codes: p0300 P0306

Using a scan tool at idle it reads about 208-221, 215-217 for highway driving, and city driving brings anything between the 208-221. The hottest coolant temp has reached 221 only for 1 minute max but from my knowledge and keeping an eye on the ultragauge coolant temp it has never ran hotter than 221.
It has a has a new radiator, thermostat, water pump, and most of the cooling hoses. Its filled with Prestone green coolant. No coolant loss. Head gaskets were done somewhere around 20-30k miles ago.

Could these problems be related in anyway? And any tips to help both of these issues thanks!

 

Have you checked to make sure your SES light hasn't been blacked out by an unscrupulous former owner? Does it light up with the key in position 1 with the rest of the bulbs in the bulb check sequence?

The temps should not be related to misfires. Sounds like you got the wrong new thermostat though, you need the OEM grey 180 degree one. your temps are at stock specification. Most of us here like to run cooler, which takes a different OEM unit with a lower operating temp.

 

180F OEM thermostat or regular?

208 is way hotter than I would be comfortable running. I'd want to see 200 absolute max.

I'm no pro at this stuff... but here are some ideas

You have a random misfire code and a misfure on cylinder #6.

When the spark plugs were done 20k ago, were they gapped correctly? I would pull the spark plug on cylinder #6 and check its spark. Try swapping a new plug.

 

As above, but check the wire too... make sure that it is secure at both the coil and the plug ends. looks for sparks in the dark under that half throttle condition. while in park of course...

 

Also, a plug wire can be killed by a bad plug. I would change the plugs and wires to cylinder 1 and 6, at a minimum.

 

Sheesh, this is a situation where I would invest no less than a couple$$, 1-dozen parts and couple days of wrenching. Replace all the plugs, wires, intake gaskets, vaccum lines, Land Rover $80 thermostat, even replace those coil packs under warranty for good measure while the intake is off and you are doing everything else. The coolant is way too hot and the misfires will continue to haunt you screwing up the exhaust system and sensors. You shouldn't put it back on the road til it's purring at 185 deg. If temps are still over 200 after the stat, need to deduce of the other parts like radiator or fan clutch.