"Low" Compression in 1 Cylinder - Bad Head Gasket?

Pretty sure I've got a blown headgasket on drivers side bank of the block but want to get some additional input. Truck is an 03 that i added a supercharger onto maybe 10k miles ago. Engine has 150k miles in total. Ran a Compression test on a warm engine and all cylinders were hovering around 220 except one at 180. Still above the lower limit but it's right there on the edge. Truck does blow some white smoke on startup but I haven't noticed any coolant loss or anything mixing in the oil.

 

Sounds like just oil burning then

 

Get one of those coolant testers that detect combustion gases in the coolant, I think Harbor Freight sells them, that would rule out a HG.
low compression might be a few things like worn rings, burned valve or just needing a valve adjustment.

 

Could be a crack in the head too. Not uncommon in the 5VZ at high mileages to get a tiny crack between the valves. cylinders 3 and 4 are the most common. Here’s the crack


Caused that cylinder to be low 20-30psi, blew smoke on startup. Smoke would be worse the longer it sat because coolant would slowly drip and pool in the cylinder over time. Coolant loss was extremely slow, barely noticeable. Oil never got visibly contaminated.
Tried the combustion gas tester on the radiator and it didn’t detect it. Didn’t find the problem til I stuck a bore scope down into the cylinder and looked up at the heads.

 

Think I'll pick up a scope and check this out. Sounds similar to what I'm dealing with. You end up picking up a new head or went with engine swap?

 

I'd suspect headgasket, its crazy how sea level gets "low" 180 compression on a 5vz, we rarely see over 170 at my altitude.

If you have a camera you can also see if it mists coolant in over night.

You wont see any noticeable coolant loss, but it will smoke and sputter on a cold start after sitting.

 

I went with new heads. That probably wasnt the right choice for me at 290k, and I spent a lot on other stuff while I had it torn apart. Looking back at it I should've bought a used motor out of a totaled truck, if I had to do it again today it would be an excuse to throw a 2uz in there. It’s a tough choice though. One of the biggest advantages from this was the experience, after a job this big I feel confident to do pretty much anything. I dont think just swapping in another 5vz would've built up the confidence and experience the same as that job.

Getting the bore scope to look up at the heads isn’t that easy, I’ll try to find the one I have and it share it. It has to be able to fit down the spark plug hole while bent to point up

Edit: Mine isn't sold anymore, but it is a 3.9mm Borescope. It barely was able to bend up to see the heads, so I would not go any larger than a 3.9mm diameter.

Also I'll throw in my summary from when I did this a last year, with everything I ended up doing and what it all cost.

 

Just out of curiosity what elevation are you at? I'm at 5300' and noticed the same thing here. Never thought of the impact of elevation on those numbers, until now

 

I'm about 1000m 3200ft and its noticeable. It's one of the easiest ways to explain air density in regards to engine performance at altitude.

 

I grabbed one of those cheap ones you plug into your phone. I'll see if that gets the job done. Regardless sounds like I'm in for either a rebuild or new heads

 

BroJohnson
I admire your protectiveness!
Then I saw you are SC’d…..(comes with the territory!)

I’m hoping just a HG!!!!!!!

However, per Time’s post, same cylinder and approx the same drop in compression

One thing for sure
Check head and if bad news
Definitely let a reputable machine shop look at damage/crack
If catastrophic damage, machine shop can get ahold of a core. Then customize the flow of head(s) to your needs.
In my experience, good MS will be less money than online vendor.
I.E. I’m guessing even LCE uses a machine shop for their high flow heads
GL
Keep everyone updated

 

You wont see the crack with a boroscope & one that will get a top image like that will be costly....
If its cracked in-between the seats which is common on some heads, first you will have carbon build-up hiding it...
2, you really wont have sufficient lighting to really see it, its a nightmare trying to navigate boroscopes sometimes let alone cheap ones that just have end view & not side view or upper view.....
Dont think you will have much compression loss with a slight crack like that, if any at all, actually very unlikely...
horoscope cylinder walls is easy enough looking for vertical scoring from a piston & cylinder wall thats seen better days...
pressure test cooling system overnight & look for coolant intrusion would be easier also, rule that out while its still together...

look at that sparkplug electrode, back side, side, for ANY faint traces of color, whatever color your coolant is....
will be hard to see, not obvious, very subtle....
another indicator that she's dead Jim...

also see how the SP threads are gummy & dark on #3 vs shiny on majority of the other spark plugs????
thats another indicator of cracked head or early signs of coolant intrusion on that cylinder...

I have no idea of orientation of your v6, but on the ford 4.0 ohv, its always the furthest back cylinder on the passenger side & the very front cylinder on the driver side...

something else to check for which is a huge tale tell sign, go under the truck with a flash light & look at where the cat pipe attaches to the end of the exhaust manifold or any of the ports on the exhaust manifold, especially the low known cylinder.
Look for ANY traces of white stains, thats coolant getting burned in the cylinder & seating out the exhaust, especially with a cracked head.

dont need to be burning through loads of coolant for there to be an issue, just enough...

 

Appreciate all of the good info here. Picked up a cheap scope online and snapped some pictures. @slater you are correct, hard to see anything in there. Checked as best I could between valves and couldn't see anything noticeable. Probably hidden by the carbon. Wall scoring looks good, think it may be worth saving if the head is slightly cracked. Going to pull them this weekend before work trip and try to get them into the machine shop.

Here's pics I could get for anyone interested:

 

WOW
those are pretty damn good pix
(as far as quality not subject matter)
What was size of your scope?
Time623 mentioned 3.9
Way interested

so glad u have a machine shop in mind

 

I’m looking on my cell phone, I think I see green at the head gasket, is it green coolant?
I see green tint at the head gasket area where the carbon line is, on the head & cylinder wall, like coolant seepage...
& obviously if you have green coolant....
not toyota red...
unless its just a strange hue from the lighting...
First picture

and I’d say I’m wrong from the looks of your pictures…
meaning for not having side or upper view, you managed to turn the scope to get a good shot of the valve area, little blurry in the area we needed to inspect though, the crack zone...
almost looks like theres a diagnol shadow at the crack zone, ide say that pic is inconclusive, you will find out soon enough if your pulling both heads...

you want to look at the cylinder wall on the inside edge of the block, with piston all the way down, vertical scoring lines.....
I see some but no idea if thats the inside end, but thats up high & minimal...

 

Could be wrong but it seems like your piston is in the way of getting a better angle on the head. Might help to spin the engine a bit so the piston is down to give you more space if that is the problem. When I did it I had to bend the borescope into a U before sticking it down the spark plug hole

I also used a cheap like $40 Amazon borescope, so I think you can get yours to point up too
That picture of the crack I posted was taken this way, that wasn’t taken after disassembly

Took quite a bit of finagling about to get an angle on it

 

Thats a giant crack,
ones ive seen on fords which have a thin bridge between the valves, are hard to see with the heads off let alone using a borescope heads on...
You actually sometimes have to remove buildup with wire brush to see Them...
The 4.0 ohv, ranger & explorer were notorious for cracked heads, cyl #3 & 4, same spot as your image...
Some borescopes to magnify things sometimes making things look larger than they actually are, makes finding flaws easier...

 

Thought the green color was odd. Running toyota red coolant so not sure where the green is coming from. Most likely oil with light shining on it just right is my guess

 

Bought something similar. $30 and it uses your phone as the screen. Honestly not bad for the $$$ paid.

 

Got it, false alarm on the I see coolant!!!
Ide lower the piston & get a good look at the cylinder wall on the inside inner wall of the block, just to be certain its not chewed-up...
would suck to do all the work ripping the heads off, to see it, "bad" after the fact...
if its been abused or compromised, thats the edge your going to see it at...

If you truly decided youre taking the heads off & sending them to a machine shop...
dont cut corners, have the rebuilt, valve job, obviously surfaced..
but price that compared to replacements....

Once you get the head off, turn head over & fill the questioning cylinder chamber in the head with water...
see if water leaks out the valve..
What we did on 3.0 rangers as they had issues with the valves getting hammered & causing minor low compression like yours..
After filling the chamber, using shop compressed air & shooting air on the backside of the valve, covering the port with a rag after inserting air nozzle tip...
If we had air bubbles coming through the water, valves were obviously leaking & suspected diagnosis was verified by that test....
We would never go through the trouble to do a leak down, as finding minor sources isn't easy & inconclusive.....