A Difficult No Start Case Study

I'm having dreams about this damn car at night!

I didn't get the part 2 notification, so I just saw it last night.

I won't spoil it for anyone, but anytime I think
" Oh, it must be XXXX",
or "man, I had a Buick that was acting like that and it was XXXX"
I'm wrong!

I really only have one or two more tests I would want to do if this thing was mine to diag.
I'm seriously wondering about the condition of the tone rings on the balancer at this point.

Oh, plus I've been eyeing that Cornwell jump pack. Looks exactly like my friend's Snap On jumper.... But you know, 1/6th of the cost...

I find this video great but difficult to watch due a couple of bad case histories --- which I might feel healed enough to share in another couple of decades.

Andy.MacFadyen wrote: I find this video great but difficult to watch due a couple of bad case histories --- which I might feel healed enough to share in another couple of decades.

Yeah, we've all got a couple of those, don't we....

This car reminds me so much of one I had with a broken camshaft not so long ago.

It might not be a very scientific test, but when I get something that cranks uneven like that, I put my hand over the tail pipe while it's cranking.
If it gets sucked in, there's usually something terribly wrong keeping an exhaust valve hung open.
Obviously you wouldn't do this if it's backfiring out the exhaust...
There may be some other variables depending on camshaft design and valve overlap, but so far it's always pointed to a valve train issue.

I really enjoy this one. Can't wait for the diagnosis and proof as Paul says.
About the YouTube notifications. Been having a lot of crap with this lately. But I check for new videos every day so it's ok.
I gave Paul some crap on his FB account by posting a picture taken from part 2. Couldn't resist

I have had only one encounter with a broken camshaft and that was on my own race car engine at some where over 6,000 rpm it became a 2 cylinder when the single over head camshaft snapped between cylinder 2 and 3, the flames coming out the Weber DCOE carb inlet on cylinder 4 were quite" interesting".

Well, hopefully Paul posts the final video soon before I go on Vacation.... hint....hint...:whistle:

All has now been revealed ............... I won't spoil it.......

It is very easy to get 'tunnel vision' when working on a piece of equipment. I can't count the number of times I was stumped and would then explain what I had done/seen to someone else just to have them say, "Oh, but did you check this?" The 'this' was usually some small point I had overlooked as I was 'sure' the problem was elsewhere.

Very good series!
I know the video is still fresh, so I'll give everyone a chance to get caught up before expanding the conversation.

My next move (after a quick visual of the balancer) would have been to put air in a couple of easier to access cylinders and check for leakage into the coolant system. In part 3, when there was evidence of coolant on the plugs, I thought that's where we were going. This test obviously would have shown nothing.

But, as mentioned in the video, a head gasket type failure severe enough to wash out the plugs would have shown up earlier as low compression pressure, so this test really wasn't warranted.

So where could coolant be getting into the cylinders if not from between the block and heads?

Well, we all know the answer to that question now, don't we?

Paul kind of seemed like he was kicking himself for not pressure testing the coolant system sooner.
I don't know that I would have pressure tested the rad right away myself considering there was evidence of an external leak to begin with.

I have changed more than a handful of 3800 intake manifolds, more than one on my own "Poniac Bonneville" from days gone by, but I have never seen one contribute to a flat out no start.

So this kind of leads to a question I've kept to myself. I've always kind of wondered if an engine with a similarly failed intake manifold (one that starts and runs) would flag a false positive on the chemical test for a failed head gasket.

I first thought of this year's ago when confronted with my first 3100 lower intake failure which resulted in cross contamination of the coolant and oil. I was trying to think of a direction test that could point toward intake or heads, considering the intake on those motors is much more labor intensive.

Today, I don't think that a failure of that type would have shown on a chemical tester because the coolant isn't exposed directly combustion gases.

However, had the Bonneville intake failure been less sever, say isolated to only a few cylinders resulting in misfires instead of a no start, world this have flagged a false positive for a head gasket failure?

Perhaps not with a chemical test checking for co², since there would have been no combustion in the effected cylinders and no co² entering the coolant system.

But do you think a 5 gas would detect hydrocarbons in the coolant for such an intake failure and perhaps point mistakenly to a head gasket problem?

We know the coolant wasn't waiting for the intake valves to open to start leaking, and considering fuel is injected when the intake valve is still closed, I could potentially see cross contamination for sure, but would it be at a level that would be evident in the overflow bottle, or would it be isolated to the intake manifold since there is no compression (from the cylinders or from inside the intake manifold) acting on the cooling system?

Stupid question?
Thoughts?

Sometimes gasket leaks only fail in one direction depending on how severe the failure. You wouldn't necessarily detect hc or co2,but if its detected,there is a leak.
Not sure if I'm on the same page with your thinking.

Say you have a GM with a 3.1 V6 and it's mixed coolant and oil. Before you sell the intake, you want to know if the head seal is compromised. Especially if there was a related overheating issue.
Is there any possibility of the intake leak flagging a false positive on the chemical test for head gasket failure?

I'm really thinking not, considering the coolant isn't exposed to the pressurized combustion gasses that it would be from a head gasket type failure. It just kind of washes down into the motor.
But I've been told in the past that it could indeed show a false positive.

I forgot about the discussion until this video and the coolant leak from the intake actually had entered the combustion chamber, and kind of renewed my curiosity.

Yeah, I think I'm on the same page. Haven't had this problem personally,but I would think that coolant leak from the intake would get sucked into the cylinder and unless the head gasket was compromised , wouldn't re-enter the coolant. Although, any fumes or hc's in the intake may possibly contaminate coolant at the leak source. I suppose you really couldn't confirm head gasket failure until you replaced the intake. Or compression test with intake off, maybe?

Let's try to think of the mechanics involved here. Maybe we can figure this out.

So for the coolant to have combustion gasses in them. The pressure in the cylinder is greater than the pressure of the cooling system. Therefore the gasses get pushed into the coolant.

Now the intake manifold is mostly in a vacuum so it would be hard for any gasses to enter the cooling system from the intake due to that fact of the cooling system being at higher pressure.

Now if oil where to leak into the coolant there might be a false positive. Not sure on that one.

Am I thinking correctly here?

Ro-longo wrote: Let's try to think of the mechanics involved here. Maybe we can figure this out...

Am I thinking correctly here?

Regarding the theory and head gasket failure, maybe the gas molecules are a lot smaller, and moving faster and right through the coolant and filling the otherwise "sealed" cooling system with HC's.
If you think about it, in extreme gasket failure after those dying horses pour all the white smoke out that they can and the coolant is all gone, HC's would probably still be present at the radiator.

However, there is no reason HC's should be present through an intake coolant leak, because the intake valve should be sealing combustion gases during the power and exhaust strokes.

I'm curious what a secondary ignition waveform would have looked like, especially after cleaning all the plugs off. How long did they actually produce a spark, would some kind of current flow through the block show itself? But I understand why it wasn't performed (everything is clear in hindsight.)

With modern OAT and HOAT antfreezes quite often a coolant leak into the cylinder will be betrayed by the spark plug nose being discoloured -- the plug will be very clean but porcelain dyed the colour of the coolant.

Because modern engine have tight control of the fue-air ratio reading plug colours is not as much used to be, but it can still provide clues to what is happening in the cylinders, the nose of a spark plug from a cylinder with badly burnt exhaust will often appear bleached white.