Compression test - White smoke *Cracked head*

So recently my truck, 3.4L, has been spewing some white smoke when cold and when it has sat for a couple days.
It'll start with a medium density white smoke at idle, and it usually clears up once warm at idle. However, yesterday morning after the truck was warm I was still blowing smoke when the engine was under load. Mostly clear at idle, but under load I could see the smoke hitting the asphalt behind me.
First thought is of course a head gasket, but it is intermittent and only happens cold and when it hasn't been ran for a few days. Even at its worst it doesn't look like that stereotypical dense white cloud that head gasket failures are known for.
I don't know exactly what burning coolant smells like, but to me the exhaust smells like something burnt. Maybe a tinge of burnt-sweet, but not as overpowering and clearly sweet as everyone suggests it would be.

I did a combustion leak test on the radiator, and it passed. That should mean there's no exhaust leaking into the coolant.

No codes, and engine doesn't feel any different.

Is this test a definitive test? Or are there head gasket failures that do not result in exhaust in the coolant system?

 

So I did a compression test,

Max variance was 30psi… with a low reading of 150 on cyl 3, double the 14 psi variance spec. However they’re all still well above the 127psi minimum spec.

Does this look like a head gasket failure?

The medium density white smoke has only happened a couple times now, and most mornings it’s very light and goes away by the time it’s warm.

 

How many miles?

Hard to tell from the lighting in the picture. Do the plugs all look similar?

 

289k
The only one I’m seeing any difference on is cyl 5, it has some carbon buildup or discoloration on the threads.
Plugs were all replaced just a few months ago

 

Does anyone have an opinion on what they would do in this scenario? Not sure exactly what my next step should be..

 

I'd look inside the cylinders with a borescope, normally cylinders burning coolant will be much cleaner than the others or even have visible coolant. If you don't see that then keep an eye on the coolant level and worry if it starts dropping.

The compression could be unrelated, something like a stuck ring. I'd try Engine Restore oil additive to help compression or seafoam to get the ring unstuck. It's nearly 30 years old, if I'm going into an engine it's either because the engine is potentially getting damaged from coolant loss or the vehicle running poorly. 30 PSI difference isn't great, but it doesn't meet my criteria.

 

You sure its coolant and not oil-burning. You could have a gunked-up ring or bad valve stem seals.

 

#5 plug looks darker/more red than #1 plug…..
As Pyral stated, if borescope used…and u see #5 piston head steam cleaned(minimal carbon buildup)
U got your answer

 

I’d check cyl 5 for steam cleaning for sure.
White and any sweet smell is for sure coolant, just a matter of how and how severe…
Usually plugs will have white crust on them if the cylinders burning coolant bad enough.

could be a tiny crack somewhere in the cylinder, as it’s present when cold (crack open, cold metal) but seems to mostly disappear once warm (hot metals expanding). I’d look for any marks or odd spots like this on the 5th cylinder too.

 

Definitely not certain its coolant, just leaning that way because of the white smoke.
I saw that you can test if its piston rings by pouring a little oil in the plug hole and re-test the compression. I'll have to try that next time I tear back into it.

I'll have to get a borescope for a proper look, I did stick a light down the plug holes to check if any were clean.
They all had pretty substantial carbon buildup visible, none of them were anywhere close to clean, couldn't see bare metal just black carbon deposits on all of them.
The cyl 5 plug was a little damp on the threads, maybe oil and carbon causing the black. Tiny bit of oil was at the base of the plug hole as well, where the plug washer sits.
I did have some very leaky valve cover gaskets, I replaced them a couple months ago but the oil may be old from a leak on the spark plug gasket I already replaced.

A crack that's sealing at temperature has definitely crossed my mind..
Its also pretty intermittent, some days its clear others its not. Seems to get worse the longer the truck sits as well. Took it camping over the weekend and both Saturday and Sunday mornings it barely smoked on cold start in the morning, by barely smoked I mean I wouldn't have given it a second thought if it did that every day. Just looked like a normal car on a cold-ish morning.

When people say 'sweet' smell, is there any other way to explain what that would be? I do think the exhaust smells wrong, but sweet is not how I would think to describe it. Maybe a very burnt syrup, but still not really 'sweet'.. The exhaust feels especially.. Toxic.. for lack of a better description, obviously you should never breathe exhaust fumes but it seems to be much more potent, makes me sick just having it idling with the garage door open, even when the back half of the trucks outside, and it seems to sticks around longer than the other cars.

Seems like everyone is more worried about the discoloration on the cyl 5 plug than the low compression on cyl 3?

I appreciate all the help.

 

Damnit
I meant #3 plug….discolored
My Fault
(I’m not even going edit my post)

Sorry time623

 

I actually misread earlier and though cyl 5 was the one with low compression..
maybe take a look at both those cylinders if you can.

I’d say coolant isnt a pleasant sweet burning aroma - But more so a sticky smell like you described.

Another thing to note if it hasn’t already been checked, is if the coolant or oil levels are changing. Lower or higher. Although this sounds small enough it may not be a noticeable change.

edit: looking at the photo again, it’s hard to tell but cyl 3 with the lower compression and slightly matte / lighter looking plug looks suspect to me.

 

I wasn’t smart enough to take a close up of all the plugs before putting it back together last night, but I did take some. Wish I took one of the oil/discoloration on cyl 5..

Here is the cyl 3 plug (low comp.) seems a little dull. I will add the threads on cyl 3 are especially rough. Not sure if they got cross threaded at some point. Also not sure if the dull appearance is a result of the rough threads, or if it’s dull because of the same corrosion that may have caused the threads to become rough.
The roughness in the threads also made ensuring that the compression tester was fully seated difficult. Can only twist the rubber hose of the tester so hard.


Here is a reference, cyl 1. Seems shinier, clean.

 

On a cooler day, when the truck will show those signs — run the truck just long enough to get up to temp or open the Thermostate.

check the coolant reservoir for bubbles coming from the radiator.

also possibly milkyness in the oil. It’ll look tan/brown and kinda separate in a pan (thing 5th grade science class, oil and water shouldn’t mix)

 

I've checked for bubbles, got nothing. I also did a block leak test which tests for exhaust gases in the coolant and it came back negative.
These tests were done when I had time after work, and it usually doesn't smoke at all in the afternoon. Think its worth trying again early in the am when its still cold?

The dipstick oil is clean, I'm hoping to avoid changing the oil as I just did it <1000 miles ago, but will do if its the last option.

 

No reason to do that just yet unless it’s looking more serious.

 

There was another 'test' I read somewhere but didn't fully understand and can't find it anymore. It was to fill the radiator completely to the top cold, and start the truck with the rad cap off and see if the level changes? Does that sound like a relevant test to see if the exhaust is pressurizing the coolant system? It did overflow the radiator, well before the thermostat would've opened.

 

I know it's already been said, but you really need a borescope for the next step. I'm betting small crack in the head, allowing just a tidbit of coolant into a cylinder. You can get some real cheap borescopes that Bluetooth to your phone, and thus your phone becomes the screen for the camera. Well worth it for things like this.

 

Should be able to borrow a cheapo borescope from work for the weekend, guess I've got my Friday night plans set.
I am really hoping to at least get this diagnosed. I've got a laundry list of upgrades I want to do on the truck, but would hate to do all that just for the motor to blow in a couple months..

 

Yeah ^^^^but
IMO you have VERY early detection of a HG or as another member said ‘crack in cylinder wall/piston’

I don’t think that test would yield any conclusive results
Borescope #1 best test

there is another test
Simple
But takes compressed air and turning crank shaft bolt (to open intake/exhaust valves)…..then u listen

there are vids out there
I did this to ‘confirm’ no compression on my Subaru (one cylinder 90lbs)
This test confirms the head/valves have no catastrophic damage

I will summarize as best I can
fill #3 combustion chamber with constant compressed air pressure

Listen to each….if you hear the air hissing….make note

Open airbox(intake valve)
Exhaust pipe end(exhaust valve)
Oil cap on valve cover (piston rings)
Open radiator cap..bubbles (HG or crack somewhere)

The only tricky part is knowing TDC and turning crankshaft to know when Intake/Exhaust valves open/close

that is thumb nail sketch
I stumbled through the process with a mechanic friend
Found that the biggest audible hiss was thru oil cap….new short block needed in my case
No damage to both heads(I sent them off to machine shop ($350) just to be safe

IMO your hissing/bubbles will be seen thru rad cap

let everyone know!!!!!