Looking for some sage like advice. Every 2 or 3 days of daily driving to work the motor will misfire and throw a P0304 code and start to overheat. I've pressure tested the cooling system with no evidence of a leak. Tested for exhaust in the coolant, again nothing. Also no evidence of anything being steam cleaned on that cylinder. Verified by visually inspecting the plug and running a scope in that cylinder. Compression is also good on #4. What should I be looking at next?

 

Start to overheat or it does actually overheat? Are you losing coolant? What T-stat are you running?

 

It's my understanding that if that temp guage moves up, you're overheating. Should have been more clear about that. Pressure gets built up in the cooling system and starts pouring out around the hose going to the water pump. Probably going to replace that hose for good measure, but that's not the root of the problem. Just put in a 180 degree thermostat. This is only happening while driving, can't get the temp to come up that far idling.

 

Do you feel a misfire or is it only a code? Eng light illuminated? Does it immediately begin to OH heat after the misfire?

What point in drive cycle is the misfire and or OH?
......

 

if you just replaced the stat then I would guess you may need to bleed it more to cure the overheating. Very common to not get it bled completely the first time. Also seems very common these days to get bad thermostats out of the box. Check to make sure that is working too. Which one did you buy? There are several but the black one from Lucky 8 is best. Check for air in the bleed hole when the engine is stone cold. If you can add any coolant at all into that hole then you found an air pocket.

That however doesn't explain your misfire on 4. Could be unrelated wire or coil issue.

 

You can feel the misfire and light flashes until it settles down. I've had it happen sitting at a light and another time while accelerating. Temp starts to go up shortly after although this last time I was about 2 miles from home when it missed and I didn't start noticing the coolant until I got in my driveway and popped the hood. Then it started coming out from that hose.

 

I can definitely tell the difference with the new stat. The upper hose running to the radiator does not get nearly as hot. I thought the same thing about bleeding it, the two things have to be related. It won't misfire for the next day or two and then here comes the drama all over again. I'll let it sit overnight and then be able to drive again until the next misfire.

 

You can feel the misfire and light flashes until it settles down. I've had it happen sitting at a light and another time while accelerating. Temp starts to go up shortly after although this last time I was about 2 miles from home when it missed and I didn't start noticing the coolant until I got in my driveway and popped the hood. Then it started coming out from that hose.

 

First course of business is to get a UltraGauge or ScanGaugeII to be able to be able to accurately monitor your coolant temps.

Without real temp readings you are clueless and we are shooting in the dark giving temp advice.
......

 

Yeah, I definitely need to grab a scanner with that will give me live data. I have a cheapo one that only gives me a snapshot. My only thing is that I feel like the misfire is the cause and the overheat is the effect.