Coolant reservoir over pressurized

Loganrobinson

Member
Joined
Apr 7, 2024
Location
Wisconsin
TDI
Alh mk4 Jetta
Hi I’m new to this page I have a quick question on something I’ve been struggling with I have a 2002 vw Jetta tdi that has been recently building up enough pressure to blow coolant out of my reservoir it’s always at different times sometimes it’s the same day I fill it other times it’s a few days after the fact I can’t seem to figure out what’s going on the car has a brand new head gasket as of a month ago it shows no signs of the head gasket failing for some odd reason it’s got clean oil and no bubbling or access pressure in the cooling system at all even when I crack the res cover it’s got pressure for maybe 2 seconds then nothing so pretty normal for a hot car but for some odd reason when driving the car will blow coolant out. When I open the res cover the coolant rushes back into the bottle and fills it back to the full line or around their. It still blows hot heat but I have noticed when idling it doesn’t blow as warm as driving any help on this would be great not sure what to do at this point it’s got the new head gasket along with all hardware a newer timing belt and assessorys a new thermostate all of which were quality parts from idparts. Thanks in advance
 

tgray

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Sep 12, 2004
Location
Marengo, IL
TDI
'02 Beetle, '05 Golf, 2000 Jetta, 2001 Jetta, 2002 Jetta
Are you sure it is blowing it out the reservoir? It may be loosing it through the egr cooler? No heat or low heat means no warm coolant in the heating core. When you develop an air bubble or air lock your cabin heat will stop or go down. The issue is to find out where the fluid is going. If you can find or buy something to pressurize the system when cold and observe the level or external leaks you may find the answer. Fluid leaks can be hard to find. Check the bottom of your radiator. That can be rusting out. Check out the flange on the back of the head or the small tube that runs around the engine. Check out the thermostat housing. It sounds like your head gasket is fine if you have no pressure or bubbles coming out when the car is running.
 

Loganrobinson

Member
Joined
Apr 7, 2024
Location
Wisconsin
TDI
Alh mk4 Jetta
Thankyou for your help I will definitely look into that stuff I’m about 95% sure it’s leaking from the reservoir because everywhere else on the engine is perfectly dry I’ve also power washed the whole engine bay let it dry completely then ran the car and the reservoir becomes covered in coolant and I can shine a light down below the coolant res and can see where the overflow has been shooting out coolant under the res I was wondering if it could be air locking but I’m unsure how to remove the bubble I’ve tried working it out by squeezing the hoses and letting the car run full of coolant with the cap off with heat on max but nothing seems to be working if that’s the issue the car developed this problem about a week after getting the head gasket fixed my friend has a pressure gauge and pump for vws we hooked it up and pressurized the system I lost about a pound of pressure in 5 or so minutes I’m assuming it was leaking from the pump considering it screws into the top of the res
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
Was there a different reason the headgasket was just replaced, or all part of this story?

Was the head checked for flatness and cracks while it was off the first time? Block decked, checked for flatness?
 

Loganrobinson

Member
Joined
Apr 7, 2024
Location
Wisconsin
TDI
Alh mk4 Jetta
I’m unsure of why it blew I bought the car with a bad head gasket from a friend who got it on trade I had the head checked at my local engine shop it all came back fine I also installed the correct hole head gasket and replaced all hardware related to it new head bolts gaskets seals basically everything top end the car ran and drove fine for about a week or two and then developed this issue the cars decently built but not to the point it would lift head bolts at all at least it shouldn’t like I mentioned in my original post it has zero signs of the head gasket failing. Is it possible for the block to warp at all I don’t know it the car was run hot at all when it blew I’m assuming if the head came back fine the block should be fine as well being cast
 

Vince Waldon

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Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
The head and block can warp independently when overheated. Ideally both are checked with precision instruments as part of a gasket change.

A coolant system that's over-pressurizing itself IS a potential sign of a failed headgasket. The gasket can fail in different ways... if between an oil passage and a coolant passage you get oil in the coolant, If between a combustion chamber and a coolant passage you get an overpressured coolant system. :)

A compression text might narrow it down, but a small gasket breach between a combustion chamber and a coolant passage will often go undetected.
 

Loganrobinson

Member
Joined
Apr 7, 2024
Location
Wisconsin
TDI
Alh mk4 Jetta
Thanks I’ll try a compression test and see what I find out I’m assuming it could have a snag breach due to how it’s acting I’m unsure of what caused it to fail if it did I’d hate have this happen again
 

fatmobile

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Jul 16, 2019
Location
north iowa
TDI
an ALH M-TDI in a MK2, a 2000 Jetta, 2003 wagon
Is there coolant flowing through the small line going to the reservoir?
 

irvingj

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Joined
Nov 28, 2006
Location
Etna,NH
TDI
2005 Jetta Wagon TDI (PD/BEW)
Isn't there a way to test for combustion gasses in the coolant? It sure sounds like a crack somewhere. (Went through that on an '82 Peugeot 504D wagon a number of years ago -- there was a tiny crack in the head from a previous overheat episode.)
 

Loganrobinson

Member
Joined
Apr 7, 2024
Location
Wisconsin
TDI
Alh mk4 Jetta
Is there coolant flowing through the small line going to the reservoir?
Yes theirs flow
Isn't there a way to test for combustion gasses in the coolant? It sure sounds like a crack somewhere. (Went through that on an '82 Peugeot 504D wagon a number of years ago -- there was a tiny crack in the head from a previous overheat episode.)
I believe they make a kit that allows you to do that that’s a good option before tearing it completely apart again
 

Loganrobinson

Member
Joined
Apr 7, 2024
Location
Wisconsin
TDI
Alh mk4 Jetta
Is there coolant flowing through the small line going to the reservoir?
Yes theirs flow
Isn't there a way to test for combustion gasses in the coolant? It sure sounds like a crack somewhere. (Went through that on an '82 Peugeot 504D wagon a number of years ago -- there was a tiny crack in the head from a previous overheat episode.)
I believe they make a kit that allows you to do that that’s a good option before tearing it completely apart again
 

jmodge

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Jun 18, 2015
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Greenville, MI
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2001 alh Jetta, RC2 w/.205's 5speed daily summer commuter and 2000 alh Jetta 5spd swap, 2" lift, hitch, stage 3 TDtuning w/.216's winter cruiser, 1996 Tacoma ALh
Let the car sit for four hours after driving and than crack the cap on the ball. If there is still pressure there at that point you have combustion pressure leaking into your coolant system.
A couple points FYI, these engines do not build heat while idling. So no heat at idle isn’t unusual. Also an internally leaking vacuum pump can over pressurize the crankcase and blow a head gasket. This condition however will give you plenty of warning by various oil leaks.

There also is a discharge relief in that coolant ball. Maybe you’ll be lucky and that failed. If you have a friend with a TDI swap theirs in and see if that takes care of it
 

Loganrobinson

Member
Joined
Apr 7, 2024
Location
Wisconsin
TDI
Alh mk4 Jetta
Let the car sit for four hours after driving and than crack the cap on the ball. If there is still pressure there at that point you have combustion pressure leaking into your coolant system.
A couple points FYI, these engines do not build heat while idling. So no heat at idle isn’t unusual. Also an internally leaking vacuum pump can over pressurize the crankcase and blow a head gasket. This condition however will give you plenty of warning by various oil leaks.

There also is a discharge relief in that coolant ball. Maybe you’ll be lucky and that failed. If you have a friend with a TDI swap theirs in and see if that takes care of it
Where should I look for oil leaks coming from my vaccume pump I did notice I have an oil leak coming out of the bottom of my pump where the bolt tightens down I took ot off replaced the gasket and noticed I still have a small oil leak
 

jmodge

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Greenville, MI
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2001 alh Jetta, RC2 w/.205's 5speed daily summer commuter and 2000 alh Jetta 5spd swap, 2" lift, hitch, stage 3 TDtuning w/.216's winter cruiser, 1996 Tacoma ALh
I’m talking an internal leak. It vents pressure into the valve cover. If you had that problem it would be evident. Probably starting with the oil cooler or ccv. You would have numerous substantial leaks. Just something to keep an eye on.
If it’s not blowing an unusual amount of oil out of several places, then that’s not the original cause of the previous blown head gasket. No need to worry about that, try my other two pieces of advice to rule out another blown head gasket or failed coolant ball vent.
 

Loganrobinson

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Joined
Apr 7, 2024
Location
Wisconsin
TDI
Alh mk4 Jetta
I’m talking an internal leak. It vents pressure into the valve cover. If you had that problem it would be evident. Probably starting with the oil cooler or ccv. You would have numerous substantial leaks. Just something to keep an eye on.
If it’s not blowing an unusual amount of oil out of several places, then that’s not the original cause of the previous blown head gasket. No need to worry about that, try my other two pieces of advice to rule out another blown head gasket or failed coolant ball vent.
Will do thanks o did just replace my coolant res bottle as well it did it with the new one and the old one unless this new one has just failed as well with the quality of parts these days I wouldn’t be surprised
 

jmodge

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Greenville, MI
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2001 alh Jetta, RC2 w/.205's 5speed daily summer commuter and 2000 alh Jetta 5spd swap, 2" lift, hitch, stage 3 TDtuning w/.216's winter cruiser, 1996 Tacoma ALh
Probably not, keep an eye on if there’s pressure in the system after cooling down. That would indicate a head gasket failure. All the hoses are in the proper places after head gasket repair?
 

jmodge

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Jun 18, 2015
Location
Greenville, MI
TDI
2001 alh Jetta, RC2 w/.205's 5speed daily summer commuter and 2000 alh Jetta 5spd swap, 2" lift, hitch, stage 3 TDtuning w/.216's winter cruiser, 1996 Tacoma ALh
A clogged heater core can also damage the head gasket.
Have you seen that on ALH’s? I’m mostly wondering because on the Toyota trucks the heater control physically shuts off the hose out of the head. I haven’t noticed any overheating issues though. I probably should run a scan gauge though
 

IndigoBlueWagon

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Aug 16, 2004
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South of Boston
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'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
Actually I had that backwards. Friend of mine had two heater cores fail because of a bad head gasket. Apologies to the OP for the mix-up.
 
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