I used a block checker from AutoZone and it did not turn completely yellow.

I get these codes p0304, p0171.

All O2 sensors were replaced in 2013. Also replaced MAS sensor. All injectors seals replaced. Throttle heater bypassed. No leaks under the car. No foaminess in coolant or oil.

Replaced injector 4 few weeks ago.New spark plugs. New spark plug wires. New coil packs. New EGR valve. New purge valve.

Was running fine until thermostat stopped working and engine went to red zone. We pulled over after we noticed engine temperature was pinned. We don't know how long it was running in red zone. After that, we've needed to refill the coolant every 2 weeks or coolant is low.

No huge plume of white smoke at cold start up.

Before I tear into the engine, I want to know what I'm getting into.

1. If it's a slipped sleeve or cracked blockcan I fix it without pulling out the engine?
2. Is there a way I can tell whether the engine is cracked or its just a head gasket replacement needed?

 

If it's cracked, no. Although even if you do pull the engine, there's not much you can do to repair it. At that point just replace it with a new, used, rebuilt, etc. If there is a sleeve slipping, some have successfully pinned the liners while the engine is in the truck. Is it tapping now though?

I would first try to determine where the coolant is going. Pull the plugs and see if any of the pistons are cleaner than the others. If you're losing that much into a cylinder, it should be obvious. If its leaking into 1,2,7,or 8 it may just be the gasket. If it's one of the inner cylinders, I think the only way coolant is getting in there is from a cracked block or liner (not unheard of) or a cracked head (unlikely) but others may know more.

Do you still have the same codes after overheating, or was that only before?

 

Ya pull plugs and try to look inside before tearing the engine down. If the block is cracked, the engine will need to come out to make repairs or replace. Don't assume the worst till you get to that point. Coolant can be going anywhere. That water jacket at the end of the block on all 4 corners is pretty common to fail. Is there coolant in the oil by chance?

 

For what its worth, I pulled my heads on mine because I was getting so many misfires and it was throwing all sorts of codes. Found out pretty quickly that a sleeve had slipped and there was damage to the block. I also found that that there was aluminum in the coolant. I don't think I would have known the extent of the damage until I pulled the heads.

 

@cvhyatt that is nuts.

 

There does not seem to be coolant in the oil. I checked by pulling the dipstick. I opened the coolant bleeder screw and it was full and under some residual pressure while engine was cool.

Next step, I will pull plugs and get a camera in the cylinders.

 

you sure that's aluminum and not stop leak? I see that sooooooooooo many times at work. I hate that stuff! In my opinion, find the leak and fix it. don't use that sh$%^& and block all the ports! Oh and as a professional mechanic...please hear me when i say that auto zone is selling parts and their employee's have no idea what a scanner does let alone how to interpret one. they SELL PARTS! tha'ts the gimmick! OOOh scanner says o2 sensor fault! we sell those! Often it isn't the sensor. just a word of advice! From the looks of your pics you have a serious head gasket leak between cylinders. I would run a straight edge on the head and block to check for warpage. The signs of stop leak and gasket failure lead me to think over heating and aluminum hates that!

 

@Pavilion - Never thought about the stop leak in coolant. Certainly possible given the condition of the engine. In any case, it is all gone now - just waiting for the new short block to come back!

 

Still getting P0304 cylinder 4 misfire.

I reset, drive a few more days, reset. Sometimes see P0174, or P0500, or P0300, or P0307, but not always. Only P0304 seems to be consistent.

New intake gasket, new plugs, new 8mm core wires, new coil pack, The O2 sensors upstream are 5-6 years old <50K miles. No leaks. No missing coolant.

Engine stutters a little on cold. Power feels normal throughout. Smooth idle and power on warm.

No huge plume of smoke on cold start. Haven't put borascope in Cylinder 4.

What should I try?

 

You should try a boroscope in Cylinder 4.

Exact same symptoms I had with a cracked block.

Put the camera in as it is cooling down while there is still full pressure in the cooling system. Then look for bubbles around the top at the seam between the heads and the block.