Boiling Coolant (water)

dokalanyi · May 22, 2017

Hi All,
Car is a 1.8T Passat B5.5
I've been running just water in my system, as I've been trying to troubleshoot this issue. How it started:

- Coolant flange at the back of the engine cracked, spilling all coolant
- Replaced flange, then pipes started bursting
- Removed Thermostat, but coolant would still boil over after sitting in traffic
- Found that the Water pump had broken off all the fins, it's was completely gone. Thought I'd found the issue, replaced Water pump, put back Thermostat.
- During the replacement of the Water Pump, something broke the timing gear, and bent valves, so needed to remove head and replace 2 exhaust valves.
- Car still overheats

I've attached 3 videos of what the coolant boils like. After about 5-10 minutes of idling. Last one I removed cap before I started idling

ATWPASSAT1.8T · May 22, 2017

Sounds like you have a few issues going on. Is the engine rebuilt now? New head gasket? Oil & coolant mixing? I wouldn't use just water, proper coolant does raise the boiling point. At your elevation water will boil at around 205F (96C), and these engines can reach that temperature, so you should certainly use the proper water/coolant mixture. Make sure you get the air out.

Not that this is of any mechanical significance, but I miss rolex from Uganda! I have great memories of your country. Though, not so much of the traffic in Kampala....

Iowegian · May 22, 2017

If the head is cracked or the gasket is bad, you may have combustion gases getting into the coolant system. This will cause air pockets, pressurization of the coolant system, etc. Did you have the head pressure-tested and re-surfaced when it was off?

semicycler · May 23, 2017

Get a pressure tester gauge and pressure test the coolant system. It will tell you if you have a leak.

V6B5APR · May 23, 2017

That is not boiling. Most probably a cracked head. I guess it overheated because of the faulty water pump and cracked the head. A replacement head with new gaskets and new bolts might solve your problem.

jjpark · May 23, 2017

Where did you source the head and valves, was everything pressure tested after this repair? Is your Aux. fan working as it should?

If you are running only water it will over heat. You need to have the correct coolant (G12) and water mix.

I also don't think that is boiling in the videos. Rather it's trying to build up pressure like it's supposed to do.

nuclearseal · May 23, 2017

x2 on cracked head and x2 on just running water through, eventually the cracked head will get worse and coolant will start getting where you don't want it to (i.e. into the oil, that's what happened to me). The pressure test will help but with the combination of coolant flange/water pump failure, probably overheated and cracked the head. Pull the fuel pump fuse, pull the plugs and crank the engine, if liquid squirts out of any cylinder you've got a cracked head.

If you're a diy'er it's not a terribly hard job, I've done it twice, plus you can get the coolant flange replaced with a better one (there are new metal ones out there, I know there is a thread somewhere), water pump will be replaced and timing belt and you're good to go.

dokalanyi · May 24, 2017

Hi guys,
Thanks for all the replies. @ATWPASSAT1.8T you're very welcome to come back

. Rolex on me. Did you have a W8 Passat with Passat World stickers?

So when we replaced the head we didn't replace the head gasket. So I took it back to the shop to replace the head gasket -- thought we'd need to resurface the head, but mechanic insists it doesn't need resurfacing. Head doesn't look cracked or warped. Unless cracking in the head can't be seen.

I'll run coolant after we've replaced the head gasket.

Iowegian · May 25, 2017

Hopefully it will just be the gasket. You also need to use new head bolts. They stretch during installation and cannot be re-used.

dokalanyi · May 26, 2017

Replaced head gasket, water still does the same thing. Although we re used the head bolts. Beginning to think the water pump is the culprit again. Is the return line to the reservoir supposed to flow continuously? And with a little bit of pressure?

Also, the heater core is disconnected (one of the pipes broke). Does that reduce the overall volume of coolant, and hence reduce cooling efficiency?

Hirnbeiss · May 26, 2017

Are you running a 505/50 mix of coolant and water? Water alone will exceed its boiling point in normal operation, esp. in tropical climates.

Does your temp gage show high temps? You should still measure the actual coolant temp using VCDS or the diagnostics on the Climatronic module. (Block 45 on: http://www.saunalahti.fi/~jues/Climatronic_Self_Diagnostics.pdf)

Ther is suppposed to be some circulation in the reservoir, just to make sure it's not mistaken for boiling. It's often noticeable when you turn the engine off and the little after-run coolant pump runs on for a bit.

If the heater core is bypassed with a jumper hose (that is, flow still allowed form one hose to the other), there should be no effect on cooling. If the hoses are blocked off, it may impact engine cooling.

dokalanyi · May 29, 2017

It was the water pump! I'd changed it about a month ago, with another used one (couldn't find a new one at the time). Replaced with metallic impellers. But I still get the oil pressure light, even when car is around 60* C

. I'm going to change oil on the assumption that the overheating made it very thin.

Hirnbeiss · May 29, 2017

Strange that the replacement impeller would fail so early, but it could have been helped along by cavitation and increased corrosion rate from running only water.

kutcht1 · May 30, 2017

What coolant were you using? That should not have corroded like that using G12 or later VW coolant.
TomK

scotts13 · May 30, 2017

Said he was using plain water. Still, that's a LOT of corrosion. I seriously question the wisdom of installing a used water pump.

dokalanyi · May 31, 2017

Used water pump isn't wise. But sometimes new water pumps aren't available. Even when available, they're chinese parts that may fail before a used low mileage OEM

kutcht1 · May 31, 2017

Must have been salt water. Was it a plastic impeller? Something ain't right.
TomK

Boiling Coolant (water)

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