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.

 

[murdoc_47]

Spent the evening taking off the valve cover. Boy was that gasket rock hard. It's a wonder it didn't weep more! Honestly, I'm pretty pleased with what I'm seeing. No sludge. No burned metal. no grooves on any of the cam lobes or rockers that I can see. The engine has never been overheated or oil starved. Hard to believe this has 316,000 miles!

Next step will be a leak down test in the next few days. Then I've decided to go ahead and pull the head. I'm encouraged by tonight!

 

[HyFlyer]

Good work @murdoc_47 ... I'm rooting for just a head gasket .

I'd be interested in seeing all the pics you want to post of a 314,000 mile motor. I'd like to see how much carbon buildup the intake and valves have. Following along.

 

[murdoc_47]

Will do! And just for anyone interested, we bought this car used at 22k miles. Since then the engine has never been apart, or had any special flush or anything extra-ordinary done to it. The only thing I've ever been strict about is always using full synthetic oil. I've done most of the oil changes myself and have always used Mobil 1. Also, as previously stated, this is my wife's car. She has to drive a lot for work so I'd honestly say 90% of the miles are highway miles, and not easy ones. She doesn't baby her machines! This engine had all original ignition (I think I replaced the plugs once, but the plugs I pulled out today were Mazda branded), injectors, and accessories. I did have to replace the belts this past year after one finally broke.

Other than that, the only things that have broken on this car have been normal wear items like tires and brakes, one blown out shock, and control arm bushings and ball joints. Like I said, best car I've ever had!

Back to the topic of my low compression, a thought did occur to me last night that was a head slapper: Valve stem seals! I was thinking about how hard the valve cover gasket had become, and then it dawned on me that old, hard worn out valve stem seals could also explain my low compression and oil consumption. They would also be the reason the cylinder 3 and 4 both have lower compression compared to 1 and 2, but not equally bad. Unfortunately the fix is still the same I think: Head removal. Though I have seen some videos where people carefully replace them with the head in place. I'll still have to remove the timing chain and cams to do it though. So While I'm there I might as well go ahead and remove the head, and send it out to be checked by a machine shop. idk. I'll see after I do the leak-down test so I can pinpoint where the pressure is leaking out of.

Good work @murdoc_47 ... I'm rooting for just a head gasket .

I'd be interested in seeing all the pics you want to post of a 314,000 mile motor. I'd like to see how much carbon buildup the intake and valves have. Following along.

 

[Lazy2.5]

I highly doubt it is the head gasket. I hardly recall ever seeing one fail on these engines. No, you're not just "lucky." these cars are known to be long lasting.

So you still have the misfire code after changing everything on cylinder 4?

Have you checked inside the engine bay for leaks? There is a plastic cover underneath the engine. You probably won't see any leaks on the ground if there are.

I also think it is just worn valve stems and/or piston rings, and highly doubt it's the head gasket.

I would certainly start running thicker oil when you have the engine back together, like 5w30. If that slows down consumption, I think that will confirm the issue.

FWIW, mine has 213k miles, and has always consumed some coolant. I have been using 5w30 for a long time. There is little to no oil consumption. Valve cover gasket has been done recently. it's been leaking intermittently for a long time.

 

[N7turbo]

I highly doubt it is the head gasket. I hardly recall ever seeing one fail on these engines.

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.

It's not unheard of. What we haven't seen are posts about valve stem seals on the NA engines.

 

[murdoc_47]

I highly doubt it is the head gasket. I hardly recall ever seeing one fail on these engines. No, you're not just "lucky." these cars are known to be long lasting.

So you still have the misfire code after changing everything on cylinder 4?

Have you checked inside the engine bay for leaks? There is a plastic cover underneath the engine. You probably won't see any leaks on the ground if there are.

I also think it is just worn valve stems and/or piston rings, and highly doubt it's the head gasket.

I would certainly start running thicker oil when you have the engine back together, like 5w30. If that slows down consumption, I think that will confirm the issue.

FWIW, mine has 213k miles, and has always consumed some coolant. I have been using 5w30 for a long time. There is little to no oil consumption. Valve cover gasket has been done recently. it's been leaking intermittently for a long time.

Thanks for the reply. I think you're right, after doing a little research it seems like the later model 2.5's really had a lot of issues with valve seals and oil consumption. Finger's crossed it's not rings. I really doubt I'll go that far with this engine.

Oh, and to answer a few questions, no, no drips at all on the ground or inside the plastic engine covers on this engine ever.

 

[Lazy2.5]

Thanks for the reply. I think you're right, after doing a little research it seems like the later model 2.5's really had a lot of issues with valve seals and oil consumption.

Yes, but yours is not a later model, and at your mileage, it's to be expected (If it is indeed the problem.)

Finger's crossed it's not rings. I really doubt I'll go that far with this engine.

Oh, and to answer a few questions, no, no drips at all on the ground or inside the plastic engine covers on this engine ever.

The only place it could be going is through the exhaust then.. I suggest to just change the valve cover gasket while you have the valve cover off, do an oil change. Put thick oil in there. Make sure there is no CEL. Call it a day.

 

[HyFlyer]

... I suggest to just change the valve cover gasket while you have the valve cover off, do an oil change. Put thick oil in there. Make sure there is no CEL. Call it a day.

how is that going to solve low compression on cylinders 3+4 though? The issue is more than just oil consumption.

 

[murdoc_47]

how is that going to solve low compression on cylinders 3+4 though? The issue is more than just oil consumption.

You're right, it is more than just oil consumption. I'm not entirely sure how, but I have seen videos online that people claim valve stem seals can also lower compression. My ONLY guess is that if more oil is burning in the combustion chamber, maybe there is excess carbon buildup on the exhaust valve that is not allowing it to seat properly. Wild guess on my part.

 

[Lazy2.5]

how is that going to solve low compression on cylinders 3+4 though? The issue is more than just oil consumption.

It's not. The vehicle has over 300,000 miles on it. It's not worth tearing it apart to diagnose and fix, in my opinion.

 

[N7turbo]

after doing a little research it seems like the later model 2.5's really had a lot of issues with valve seals and oil consumption

That was the batch of exhaust valve seals for the 2021 Turbo models. It did not affect the NA cars.

 

[RedBaron]

I have seen videos online that people claim valve stem seals can also lower compression

How could that be? When a compression test is done, the valves are closed, and the stem/seals are blocked.

 

[Lazy2.5]

A quick search online indicates that issues with the valve stem seals are generally not very involved in lowering compression, but it's possible, and unlikely to be the cause in this case.

Since you have oil consumption, I am going to go with piston rings.

Whether you want to replace them and hope for the best, or just send the car as-is, of course if your choice.