Signs of a Blown Head Gasket

[murdoc_47]

Our beloved 2014 CX-5 has served us mighty well for many years. She's got 314k miles on her now and she's got her first major trouble. I'd appreciate some help on what troubleshooting to do next.

On my wife's way home she got a check engine light. I pulled the code and it is a P0304. Cylinder 4 missfire.

Here's what I did... Replaced Spark Plug, Coil and fuel injector. Same code. Checked with a spark tester and confirmed spark.

Engine runs slightly rough at idle, but seems to run fine above idle all the way up to highway speeds. No seeming loss of power or sputtering.

When I pull the wire harness going to each coil while the engine is running, most make a dramatic change to the engine, except #4, it changes a little, but doesn't really fall on its face.

The other symptom is that the car has been "using" more and more oil and coolant over the past year. Yet I never see any drips under the engine, and I don't see coolant coming out of the exhaust. But when I wipe the inside of the exhaust tip, my finger does come out very black. When my wife pulled in the other night with the check engine light, there was no oil on the dipstick.

So, my working theory at this point is that the Missfires is caused by low compression in the cylinder 4. The low compression is (hopefully) caused by a blown head gasket. Which would also explain the loss of coolant. As for where the oil is going, I'm not positive. I'm guessing it's going out with the coolant.

Oh yeah, the engine does not overheat.

My next move is to order a compression tester off of Amazon and get compression reading for each cylinder. If that confirms low compression I guess I'll pull the head and look for signs of a blown gasket.

Does this seem reasonable? Any other suggestions?

 

[erhayes]

Appears you have covered most everything. I would however, open the radiator cap(engine off), and start the engine. A leaking HG will show a lot of gas coming out of the coolant.

 

[murdoc_47]

Today I performed a cold compression test. Here are the results. Pretty much what I expected:
Cyl 1 = 180 psi
Cyl 2 = 173
Cyl 3 = 115
Cyl 4 = 73

Double checked and the oil is not milky at all, and the coolant is not dark. Here's my current theory:

I think there is either a crack in the head, or a blown head gasket near the high pressure oil line going up to the head. (From watching youtube videos, I think this is down near cyl 4) It is leaking oil into the cylinder 4 and being burned off. Not enough to see visible white smoke, but enough to really foul the exhaust tips.

My other thought is that the head is just warped down by cylinder's 3 and 4. That would explain why the pressures get better the further away from 4 I measured.

Next steps:
1. Perform a leak-down test
2. Perform a running test to see if exhaust is being vented through the coolant.

 

[HyFlyer]

So, at 314,000 miles why go through more testing past low compression on two cylinders? Would you spend the time/money/effort to replace the head gasket or further on a high mileage motor? How about a replacement instead?

I appreciate your post here and taking the time to write about what's going on with your car and commend your diagnostic abilities for sure. I'm not being negative to you, just thinking logically towards the future.

 

[N7turbo]

I'm seeing more of these head gasket failure posts from the 2014 model year lately. And my mechanic brother just repaired one as well.

I would probably replace the head gasket but while I'm in there, have the cylinder head and intake system thoroughly cleaned out, including walnut blasting and/or ultrasonic parts cleaning. There's undoubtedly a lot of carbon buildup in the intake runners and valves and possibly the throttle body as well and now is the time to do it.

 

[murdoc_47]

Trust me, I'm having the same thoughts for sure. Amazingly the car isn't in terrible shape. Surprisingly rust free. Especially since I live in Ohio. Brakes are new-ish. Tires are in decent shape. Good HVAC. Has the Navigation, swiveling head lights, and moon-roof. Transmission is strong, even thought it has NEVER been serviced!! We've definitely gotten our money out of this car. I'm not exaggerating to say it is the best car I've ever owned. Not sure if we just got lucky or what.

So, my dilemma now is how much to invest in it. If I could get it running again it would be a good first-car for my daughter. I think it is worth it to go a little further. I have a fair bit of mechanical knowledge and tools, so I can do all of the work myself. Except, I can't really do an engine swap. I Don't have a lift, or an engine hoist. So I couldn't lower an engine out, I would have to strip it down, buy a hoist and lift it in/out.

So by my math, if the issue is just blown head gasket I'm looking at buying at a minimum:
1. Head gasket
2. Valve Cover Gasket
3. Head Bolts
4. Timing Chain and components (Might as well since I'd be in there)
5. Cost to have the head checked and skimmed at a machine shop.

If the head is cracked, I'd likely need a replacement head. At that point I'm probably near the cost of a replacement engine. I've found some with around 120,000 miles for $1000 - $1500.

Thankfully we have another car my wife can use, so I can take my time with this. I think it is definitely worth at least pulling the valve cover, looking around, and probably pulling the head. If it's a nightmare in there and the cylinders are scored, I can just slap it all back together and sell it as a good parts car or something.

 

[N7turbo]

Hopefully that is the only issue.

If it ends up being just a gasket replacement, make sure to take pictures and maybe make markings of the timing and don't let the motor turn until you put it back together. Based on the posts here, you don't want to have to mess with that if it ends up being off.