'91 Jetta 1.6D Not Building Coolant Pressure

[CODE4LS1]

Hey guys, I have owned a few VW diesels over the years, but this one has me stumped.

My cooling system NEVER builds pressure and especially on warm days in SoCal, once the car is parked/not running, a lot of the coolant will boil up and out of the coolant overfill.
I have replaced the cap twice, thinking the 1st one was defective.  Then I bought a new coolant reservoir bottle thinking mine was cracked and bleeding off pressure.
I see no signs of coolant seeping from the radiator, hoses or heater core (heater core was replaced a couple months ago).
Now, as long as the engine is running (coolant circulating), it never overheats/boils over.

That in the world is causing the no pressure situation?  If anything, the problem is usually too much pressure when a HG goes south.

Any input is welcome.  Now that it's getting warmer, my car loses a good bit of coolant once parked almost daily.

[damac]

Don't get what you mean by no pressure since it boils out of the cap?  Also if you are running and driving how is there no pressure?

Time to go over the complete cooling system, make sure water pump is moving fluid.  Take your thermostat to pot on the oven to verify temps and opening/closing action.

It sounds like its a head gasket if the unions are all good, weakest link is the cap in reservoir at less than 20 psi blowoff

You positive if you top your car off to a line on reservoir cold and drive it that it isn't losing any coolant?  Hard to believe


Do you have the vw oil cooler on your car, have you checked your oil for coolant?

[CODE4LS1]

Heat soak after the engine is shut off causes the coolant to expand.  I'm assuming because of heat expansion, the coolant level rises up and out of the overfill hole in the reservoir bottle, as there is no pressure to prevent this.
I have already verified proper operation of the thermostat.  The car does NOT overheat at all while it's running. Completely normal.  I have also verified coolant circulation.  As far as I can tell anyway, every aspect of the cooling system operation is normal, save for no pressure.
I even looked to local parts stores for a cooling system pressure tester, but the ones they have do not work on the VWs.

[air-cooled or diesel]

I had a similar problem kind of once or twice,
how do you know it has no pressure? Make Sure you have enough coolant in there, my probs occurred when I couldn't seal an 'open' system; once I had to drop coolant and didn't have a new oring, so I had to lug it for 300 miles, filling with water every 50 or so miles, water level in coolant reservoir didn't read right, so I had to fill up and go a few miles and top off, as there were hot spots pushing water(in my/this case) up and being it was circulating it would stay cool enough. but was in reality very low.
a pin hole leak in system will relieve pressure in system, most show a coolant leak, and you end up topping cooling sys often enough. check all water connections, im guessing putting pressure on system will tell you the most, no more that about 7-10psi. if you have the equipt to do that.
I recently changed out all my coolant lines

[CODE4LS1]

I'm wondering if there is a failed water jacket seal on the HG close enough to the edge, causing pressure to bleed off.  Anyone know where I can find a correct pressure tester for VW?  I'm certain that will definitely help me pinpoint where pressure is bleeding off.

[air-cooled or diesel]

run engine hot, with soapy water spray, cool area with spray and look for bubbles, don't cool too much with spray, get wet and let evaporate off.

[air-cooled or diesel]

I it was HG, water would be going into cylinder, and out exhaust; pressure from cyl would be going in cooling sys; or/also in oil sys.

[vanbcguy]

Wait wait... You have no pressure when driving, then it boils out the overflow when you stop?

The overflow is the pressure regulator. I know you've replaced the cap and reservoir but something has to be going on there. Otherwise it wouldn't boil over from there - it can only do that if the cap is allowing coolant pressure out, which it is only supposed to do at 20ish PSI.

If it were functioning properly and you had a pressure leak elsewhere then that's where the coolant would be coming out when the system boiled over, not at the reservoir.

Sent from my HTC One XL using Tapatalk

[air-cooled or diesel]

right but a boil over in an otherwise sealed, or leaking system goes easily up to reservoir, at idle a system with problems the hot spots lower in engine/ and in head don't get enough circulation; boiling coolant, sending it up to the reservoir. soapy water will show pressure leaks.

[theman53]

Heat soak after the engine is shut off causes the coolant to expand.  I'm assuming because of heat expansion, the coolant level rises up and out of the overfill hole in the reservoir bottle, as there is no pressure to prevent this.
I have already verified proper operation of the thermostat.  The car does NOT overheat at all while it's running. Completely normal.  I have also verified coolant circulation.  As far as I can tell anyway, every aspect of the cooling system operation is normal, save for no pressure.
I even looked to local parts stores for a cooling system pressure tester, but the ones they have do not work on the VWs.

what do you mean by "overfill hole in the reservoir bottle."

[TylerDurden]

You got the upper rad hose like this?


That small tube needs to constantly piss coolant into the expansion tank to purge air from the system.

[GEE-BEE]

Thats the a/c model hose

http://www.autohausaz.com/search/product.aspx?sid=cstv2g45g00rup55z1kpvy45&makeid=800026@VW&modelid=1283352@JETTA GL&year=1991&cid=16@Cooling System&gid=10068@Radiator Coolant Hose

I make those also, there was some people that the overflow hose was clogged...

[air-cooled or diesel]

run engine hot, with soapy water spray, cool area with spray and look for bubbles, don't cool too much with spray, get wet and let evaporate off.

Wait wait... You have no pressure when driving, then it boils out the overflow when you stop?

I don't mean run hot where it boils over, run till good and warm, have someone rev to 1500rpm, and spray soapy water at every connection and hose,

[CODE4LS1]

Alright....So I replaced the head gasket (the car head a mechanical head on a hydraulic block) and cylinder head with the correct hydraulic. STILL does not build any cooling system pressure.  My commute home is mostly uphill, 24-26 miles, and it does not heat up.  Both upper and lower radiator hoses are hot.  Thermo opens when it should.  The car does NOT run hot while running.  It hasn't been too hot since the head and HG replacement so there have been no coolant loss like before, through the puke hole in the coolant reservoir.
It just will NOT build pressure.

Also, since my last post, I have replaced the coolant reservoir bottle AND bought another reservoir cap in case the previous brand new one was faulty.
I'm at a loss.  New rebuilt (correct) head, new HG and new bolts.

I'm open to any ideas a this point.

[CODE4LS1]

Yes, that is the hose I have, as I have A/C.

You got the upper rad hose like this?


That small tube needs to constantly piss coolant into the expansion tank to purge air from the system.