1.6na head gasket symptoms but no signs when heads pulled

[FrankenDiesel]

I've been noticing coolant consumption and there hasn't really been the tall tale white smoke out the tail pipe. Car runs good otherwise. I did notice oil in overflow.

I couldn't see a leak under the car for coolant. The core just blew two days ago but likewise I never noticed coolant in the cabin or a smell, and probably refilled the system 4-5 times in the past few months. I replaced a ton of hoses and flanges with no success.

However, I pulled the head today and the gasket doesn't seem to have hairline cracks or anything of that nature. It has the cracks between valves, and some decent sized prechamber cracks. From that I do not see how coolant would have entered the combustion chamber.

I also noticed that the car pressurizes the coolant quickly, which often is a sign of compression gasses leaking into cooling system. Again a quick look didn't yield any cracks from the combustion chamber on the head to the cooling jackets.

I was wondering if anyone can point me to an idea of how to pinpoint the source of coolant consumption. I do have an extra idi head but do not recall if it had prechamber cracks. However the car that my extra head was pulled from exhibited the same symptoms just not as excessive.

Just trying to get things set for a 14 hour trip to sowo

[ORCoaster]

By any chance did you measure the compression in the cyls before yanking the head?  With 4-5 refills going you either have a leak or didn't get it to open up the thermostat when you filled it up initially.  I have trouble getting my coolant to fill well right away because of the extra hoses going to FPHE for the Veg Oil addition.  It seems to take a good amount of revving around town to get the upper hose to fill the first heater attached to the filter.

Seems to drink about half an overflow tank to get that to fill up and cycle through. 

With all the fluid you are loosing I would opt for some of the dye that glows under an ultraviolet light to see if you have an internal or external leak that is just not showing itself with drips or fluid you can see.   

[FrankenDiesel]

I didn't measure compression because I figured it was pretty definitive between the coolant loss with no trace, high mileage, oil in reservoir, a cool system pressurizing quickly, etc.

When I fill the car with coolant I usually do this. Remove coolant temp sensor, fill the car with it off until it spews out of the flange on the head. Put in coolant temp, remove upper rad hose from rad, fill that til it has coolant, re connect. Then I top off res, and start car with heat max. Usually run it for a good while, massaging hoses. When its cold, replace what's missing.

However, these diesels do run cold, on average mine runs a hair or so above where the lowest white on gauge is. I have an aftermarket fan with a temp probe which kicks on very early. It could be a possibility, but I am wondering why it would be that low after all these times refilling it, I would adventually think it would be full.

Not to mention the concerns I listed above with the coolant pressure and such.

[ORCoaster]

I run mine after a fill until the fan comes on twice.  I have a way to set a higher idle on the IP with a pull out cable in the cab.  That bumps the Revs up to 1500 or so.  At Idle I don't think the fan would ever come on.  Reading your description I would knock that fan sensor back to get the engine to warm more than what you currently have going.  Like you say, diesels run cold, but they don't have to, and really shouldn't. 

Running a Veg Oil system on my car and knowing that stuff needs to be about 160 going into the IP to do well at the injectors I have this cool blue colored digital sensor that gives me instant readings from the sensor bulb.  I had it on the input line for when I ran Veg Oil but now that I can't I switched it over to the hose that goes to the coolant tank.  I can see the temp climb all the way to 174 and at that point the fan comes on.  I run with the gauge just one over to the right of the middle of the stock gauge.
 

[FrankenDiesel]

So here's the update. I took my spare head, cleaned it, and removed the cam. There are small valve cracks but also as big as 3/8 prechamber cracks. Right now I have water on the valves to see where they leak. This head also had a coolant consumption issue I believe, but also an instant coolant system pressurizing concern when the engine was started cold.

I don't see how the cracks between the valves can cause consumption as the water jackets are around the chamber not above/in them.

I'm gonna be measuring the heads for warpage tonight. Anyone recommend a home straightedge or know the warpage allowance?

[vanbcguy]

If the cracks between the valves go deep enough they can hit the water jacket, but yes they have to go extremely deep in to the head.  Prechamber cracks however are a big deal, those need to be replaced or you might as well just toss a handful of inconel chunks in to the engine before putting the head on.

[FrankenDiesel]

Well that brings me to a few questions. I thought precups were NLA?

Also I remember reading that some crackage in precups is also normal. I believe it, being that the two idi heads I've pulled ran perfect, yet both have pre cracks and valve gap cracks.

I'm just trying to figure which head to put on. I don't want to do a full rebuild. I'd rather just go tdi

[vanbcguy]

Cracks between the valves are normal and OK to run as long as they are thinner than a dime.

Cracks in the precups are COMMON but not NORMAL. They are not OK to run. A precup popping out or cracking in to pieces will destroy the piston and head as a minimum and may go as far as taking out the block and/or the rod.

I'm not sure where you get them but I've definitely seen people getting new ones.

[ORCoaster]

Tolerance on warpage is .004 inch
Having a very good straightedge is critical.  Might need to take it to a machinist if you don't have anything around you trust to be straight and can do the job. 

[92EcoDiesel Jetta]

Are pre cups the same for NA and turbo heads?

[clbanman]

I had very similar symptoms to what you describe on a Ford engine, and eventually found that there was a vertical crack on the cylinder wall that looked like a minor scratch when the block was cold.  It was enough to pressurize the coolant system and push coolant out of the overflow.  When the engine was shut down the coolant level would drop but never got any into the oil.