Pressurizing coolant only under high boost... Stretched head bolts?

[gretaTUNEberg]

I just bought a 2003 Jetta with 520000km. When going up big hills and passes, the coolant pressurizes and boils over. Both the previous owner and his shop suggested that since there's no mixing of oil or coolant, rather than being the head gasket, this is likely head bolts which have stretched and are allowing air or exhaust to seep into the coolant under heavy load. They recommend head bolt replacement.

Has anyone else experienced this?

Can I tighten the head bolts a small amount first to see if it helps, or should I just replace them?

 

[oilhammer]

If you are 100% certain that it is NOT getting too hot, and it is for sure PRESSURE, then I would make plans to R&R the head and have it professionally checked out. If there is a place where combustion pressure is getting into the water jacket, you likely are not going to be able to fix it by overtorque or retorque of the head bolts with an MLS head gasket.

Also, is there any soot in the coolant?

Just because oil and coolant are not mixing doesn't mean the head gasket and its sealing surfaces are not the culprit.

Love your username, BTW, and welcome!

 

[gretaTUNEberg]

Thanks for the welcome! It's my first mk4/ALH, and she's a beauty!

The temp gauge is a steady 90C until there is a TON of gasses in the coolant, then it starts to rise (presumably its hot gasses and steam affecting the sensor at that point), at which point I have to pull over and open the coolant bottle and the line where it tees in to the upper rad hose to let all the air escape. But this only happens after loooong climbs - here in BC, that means mountain passes.

There's no obvious soot or contamination of the coolant.

And yes it is definitely pressure, when I vent the line and the coolant bottle there is a ton of air that comes out.

Is there any major risk to over tightening the stock head bolts a little bit to see how much of a difference it makes?

 

[oilhammer]

Probably not any risk, I doubt you'd strip the block or anything. Just know that the initial torque of the head bolts is already VERY tight. I'm no tinkerbell, and that last 90 degrees with a long 1/2" breaker bar is a workout even for me doing all 10. So I don't think you are likely to get much more of a turn out of them.

 

[Zak99b5]

It could possibly be the EGR cooler, unless that has been ruled out.

 

[oilhammer]

I thought about that too, but I've never known an ALH EGR cooler to fail, and the couple (AHU) and several (BHW) EGR coolers which are a similar Valeo "log" style design I have seen fail, they go the other way... coolant blows into the intake and exhaust, creating a giant steam cloud out the tailpipe.

 

[gretaTUNEberg]

The egr cooler was already deleted by the previous owner

 

[jayb79]

This is sounding like my same head gasket (turned out to be a warped head) problem. Would only get hot if I was into the boost. I drove it that way for about 10k miles, then changed the head gasket and it would be good for another 5k and do it all over again. After about 60k miles of this abuse, I finally changed the head and it's great again.

 

[P2B]

You could try running it unpressurized temporarily (remove the o-ring in the ball cap) but as OH said it needs a new HG and surfaces checked for flatness while it's apart.

 

[mittzlepick]

Even with cap off you will atill blow coolant out ive tried it all with my beater. Considered a plumbing vent to drag out its eventual replacement. But we have a 55 gal drum of coolant at the shop.

 

[gretaTUNEberg]

Is it safe to run the cooling system unpressurized like that?

 

[jayb79]

I had my system rigged up with an overflow plumbed into the overflow from the ball. When the boost would blow out the coolant I could catch most of it and dump it back in. I still run without an oring in the coolant cap(determined not to change the heater core). As long as it's not pushing any more power than stock I've never had an overheating problem. My original overheat happened because I had the Every mod going and I got carried away on a long high speed hill climb with no o-ring and it got hot. Coming up on the 500k timing belt and I still love this car.

 

[gretaTUNEberg]

Does running without the o-ring in the coolant bottle increase the risk of overheat because of decreased coolant system pressure?

 

[Vince Waldon]

IMHO the short answer is "yes"... the system is designed to operate pressurized (15 psi) on purpose.

The longer answer: dunno where in Canada you live, but say for example at sea level, your 50:50 coolant will stay liquid till 133C with a pressurized system but only to 107C with the system open to atmosphere.

When it boils over (turns to steam) it can no longer cool the engine effectively or uniformly, and since the rad fans come on somewhere around 97C your wiggle room is 10 degrees unpressurized, as opposed to 36 degrees when properly pressurized.

Probably not a horrible risk in a Canadian winter for short drives when the t-stat may not even open, but if you're having the kind of summer most Canadians are having you may want your cooling system at full capacity.

 

[P2B]

I've driven mine several hundred km unpressurized in order to get home with a leaky radiator and temperatures reported on my scan guage were the same as normal.

The highest l've ever seen was 105C when stuck in traffic on a 30C day with the AC on maximum - which is uncomfortably close to the boiling point of unpressurized coolant.

So IMO there's little risk to running unpressurized, especially if you can monitor temperature accurately - which the cluster guage does not do.

 

[Nuje]

The poor man's Scangauge - just plug into the OBD port and have little HUD showing a few different parameters, accurate coolant temp being one of them.
Just one of a few different options available there, so look around.

 

[gretaTUNEberg]

I had my system rigged up with an overflow plumbed into the overflow from the ball. When the boost would blow out the coolant I could catch most of it and dump it back in. I still run without an oring in the coolant cap(determined not to change the heater core). As long as it's not pushing any more power than stock I've never had an overheating problem. My original overheat happened because I had the Every mod going and I got carried away on a long high speed hill climb with no o-ring and it got hot. Coming up on the 500k timing belt and I still love this car.

Suuuper curious how you plumbed this! It's probably what I'll do until I can replace the head bolts and HG

 

[csstevej]

I like the HUD display…..

 

[jayb79]

The overflow tube pops off the coolant bottle then find a piece of tubing to fit it. I put a 1 liter oil bottle next to the washer, drilled a hole in the top and put a copper 90 in it and put the tube on.

 

[P2B]

The overflow tube pops off the coolant bottle then find a piece of tubing to fit it. I put a 1 liter oil bottle next to the washer, drilled a hole in the top and put a copper 90 in it and put the tube on.

The OPs '03 should have the newer ball design, no overflow tube. Not sure it's feasible to capture overflow.

 

[jayb79]

The part that was removed is on top of the fuel lines. I haven't had any coolant overflow since the head was changed, I just left the bottle.

 

[gretaTUNEberg]

The OPs '03 should have the newer ball design, no overflow tube. Not sure it's feasible to capture overflow.

Mine has a hole which drains down the side of the bottle under a little removable cover, I should be able to run a small tube through it

Thanks for all the good info so far folks!

 

[gretaTUNEberg]

Ps - compression tested at 390,378,350,382... Could I still have a damaged head gasket even with these readings?

 

[Genesis]

Yes.

 

[csstevej]

If you’re blowing coolant……you have a bad head gasket.
Cylinder #3 is a little low , that’s where you could be loosing pressure.

 

[Vince Waldon]

Ps - compression tested at 390,378,350,382... Could I still have a damaged head gasket even with these readings?

Sometimes the issue is that the head is lifting slightly while hot and under heavy boost (like passing or hills, sound familiar?!)... exposing a void in the gasket.

Unfortunately not something you will discover in your driveway at cranking speed... which is why a compression test for a headgasket issue can give you a definitive "yes" but a very indefinite "no."

 

[red16vdub]

If you’re blowing coolant……you have a bad head gasket.
Cylinder #3 is a little low , that’s where you could be loosing pressure.

Absolutely bad head gasket, it’s not the end of the world. Usually an easy fix.

 

[jayb79]

If it's been overheated the head will be most likely warped. I changed 2 head gaskets before the denial of bad head sunk in. Mine only overheated once.

 

[oilhammer]

I'd never pull a head off without having it professionally checked by a competent machine shop. Or, if you yourself are of such a holder of said skillset and tools.

 

[gretaTUNEberg]

UPDATE

I ended up replacing the stock head bolts one at a time with 12.9 rated non TTY ones from Grainger at $1.50 each. Torqued to 125, drove and cooled, retorqued. Took it for a few good highway pulls and the problem seems to be at least 90% improved. I'm able to open the sealed and pressurized coolant bottle right after pulling over with no boilover, and there isn't nearly as much pressure in the system as before the bolt change - perhaps no more than normal operating pressure? I'm not sure. It might not be a perfect fix, and I might still have a HG replacement in the future, but I'm pretty happy with it for the time being. Markedly notable improvement.

Thanks to all the people who replied here with suggestions!