Leaking radiator - run unpressurized?

[P2B]

My '03 suddenly leaked 2l of coolant on the drive to the cottage the other day. The radiator has sprung a leak between tank and core. I topped it up when I arrived and it has only leaked another 100ml or so while parked for two days.

I have a nearly new spare radiator at home 180km away, and 8l of mixed coolant in the trunk.

I'm assuming it would be best to run the cooling system unpressurized on the trip home?

Simon

 

[Mongler98]

it will run un pressurized with a crack in it. as long as its not running low on coolant, go for it. had a similar issue on my escape last month.
just take a few gallons of distilled with you DO NOT RUN LOW ON COO(LANT. its literally the worst enemy of a TDI and most engines to run too hot. the first place to suffer from low coolant is the head as some of it will have coolant but not all of it as it flows low on coolant THIS WILL WARP IT.
just keep the coolant ball filled and you will be fine. if you can do that then tow it. or risk it. your call, but head work is NOT FUN and way more than a tow.
if it was me, just pull over every 10 miles or whatever and top it off if it needs it. no harm in running no pressure but you will have boiling issues. the more water you add the lower the boiling point of the coolant it gets and with no pressure it will be even lower. so not difficult to damage things with no pressure and slightly low on coolant and mostly water...

 

[PakProtector]

14 psi gets you to about 240F with pure water. As Mongler said, running low is to be avoided. Completely. If it were me, I'd grab enough to replace what leaked out along the way and keep diluting it with water. I would not run unpressurized.

You are going to drain most of it on replacement of the heat exchanger, but to account for the dilute stuff left in, just run higher concentration. Check it after it mixes. Adjust as required if it is light on glycol( drain some and add concentrate).
cheers,
Douglas

 

[P2B]

if it was me, just pull over every 10 miles or whatever and top it off if it needs it. no harm in running no pressure but you will have boiling issues.

The low coolant alarm will tell me if I need to pull over and top up.

Why would running with no pressure cause boiling issues? It normally runs at 93C, below boiling point.

 

[mittzlepick]

Reads 93 boils at 100 but even below boiling you lose water and im sure you get boiling in places along with cavitation/bubbles. I tried to run with cap off after screwing in an air fitting to red green my coolant bottle after nipple broke off. She decided to call low coolant as i got on George Washington bridge of all places. Turns out the nipple held pressure anyway and made it another 800 miles to georgia and got a coolant bottle after stores were open. What a road trip that was.

 

[Mongler98]

The low coolant alarm will tell me if I need to pull over and top up.

Why would running with no pressure cause boiling issues? It normally runs at 93C, below boiling point.

because the boiling point of all liquids is directly affected by its pressure. In the case of coolant, adding more water will lower the boiling point as well.
the issue isnt that it will boil all the water, more so that it will micro boil creating hot spots where coolant isnt getting 100% of the time from low coolant, this creates steam that pushed OUT the coolant from that area, making a hotter and bigger spot, pushing more coolant out and then you have a wrapped head. keeping it topped off you probably won't have that issue.

 

[P2B]

Unpressurised FTW

I tried running pressurised but the low coolant alarm went off within 5km of reaching operating temperature and it took almost a whole litre to top off, so obviously that wasn't going to work with 180km to go. I removed the o-ring from the cap.

Despite Mongler's dire predictions the ALH actually ran 2C cooler without pressure, and only lost another 300ml or so the rest of the trip - not quite enough to trigger the alarm again. I assume the thermostat must have opened a little sooner without pressure.

It makes sense to me that unpressurised would work because the boiling point of 50/50 G12 at sea level is 106C, but my ALH normally runs at 93C, leaving a smaller margin than it was designed to have but apparently still enough.

Not looking forward to getting the lock carrier into the service position to replace the radiator. As far as I know it's never been done on this car, so the fasteners have seen 18 Canadian winters...

 

[turbocharged798]

Leave the cap loose. It won't hurt a darn thing. These engine produce so little waste heat that it doesn't matter much. If you are really worried just keep the heat on full the whole way.

Way too many armchair mechanics around here lately.

 

[Zak99b5]

Service position for the radiator makes this job pretty easy. I just replaced mine. At first I thought I was a bunch of extra work (B5 radiators are like two pins then lift out), but on the A4s service position takes a tight job and makes it pretty easy.

Just make sure you have long bolts of the proper size to replace the bumper bolts for the rad support. I did not and tried to improvise and caused myself a few headaches.

 

[P2B]

Service position for the radiator makes this job pretty easy. I just replaced mine. At first I thought I was a bunch of extra work (B5 radiators are like two pins then lift out), but on the A4s service position takes a tight job and makes it pretty easy.

Just make sure you have long bolts of the proper size to replace the bumper bolts for the rad support. I did not and tried to improvise and caused myself a few headaches.

Thanks.

I have done this job before and have the long bolts needed. Usually the worst part of the job is removing the bumper cover fasteners because they get pretty crusty from road salt. I sprayed penetrating oil this evening, hopefully it will make things a bit easier in the morning.

 

[Zak99b5]

Upstate NY isn't much kinder to fasteners. I had to snip the bumper cover to get it off one seized lower bold (behind small grille) and drill out one fan shroud screw and the screw that holds the A/C bracket to the rad. Really, not too bad considering.

 

[jimbote]

I ran unpressurized for a few months in my beetle while I waited for the time to do a heater core. Apparently my experience with overheating seems to differ radically from some folks. I severely overheated that same car. Not even sure how hot it actually got but ran it without coolant, as in zero, for about 25 miles at highway speed. Long story, but i drove it for another trouble free 50k miles after with only standard maintenance. It ran perfect when i sold it at 303k miles and i saw it go through at least two other owners after that. This incident and others has led me to believe the ALH is one of the toughest engines ever built.

 

[DuraBioPwr]

Running unpressurized can create localized boiling in the head and potentially other areas of the engine. Possibly the water pump as it moves fluid and thus experiences a pressure differential. Its the expansion of liquid in the system that mostly causes the pressure in the system, not the fact your at boiling point or not. The engineers know how much volume is in the systems and thus leave that much air gap in the pressure tank/ reservoir based on liquid expansion. This expansion creates enough system pressure to mitigate the effects of localized boiling. Higher pressure = higher boiling point. Localized boiling can create cavitation damage. Also in areas of the head that are hot and now experiencing boiling cannot transfer heat through the boiling area as well and can crack. The pressure keeps it liquid in all areas of the system. The engine is not 190deg everywhere, that is the mean of the liquid from all areas.

That being said running for a bit unpressurized wont hurt it, but would not do it long.

 

[jayb79]

An ALH in STOCK tune with a light load will run unpressurized without any trouble. I have been running my golf this way for years (don't want to deal with the heater core). Turning the power up or heavily loading it is a different story.

 

[P2B]

Had to drill out several fasteners despite thoroughly cleaning out the heads with a dental pick before attempting to remove. Parts bin took a beating because none of them were fit to reuse - 18 salty winters will do that. The heads twisted off the fender to lock carrier bolts with very little effort, no luck drilling out the remains so they are now absent.

The spare radiator looked crustier than I remember, but it had only been in service two years so hopefully will last a few more.

Back under pressure

 

[BobnOH]

With the fun time even getting to the radiator, I would spend the$70 to $140 and get a new one.,

 

[P2B]

I hear you, but I get enough grief for hording VW parts, I don't need more for buying new when I have used on hand ;-)