Boiling over

Any ideas on what I should do next with my daily drive as driving home today the coolant got so hot it boils out of the cap and is leaking coolant..
When I switch the engine off you can hear a gurgling sound from the thin hose going to the expansion tank from the radiator.

It’s a standard 88 cabriolet GTi DX and I thought thermostat as the bottom hose and housing was not as hot as the top hose.
When the engine cooled I removed the expansion tank cap and checked for a flow of coolant, which there was.
So … new thermostat and coolant later I burp the coolant system and fit the blue cap… things heat up and the fan kicks in… I wait then just before the fan would kick in for the second time the coolant boils over…

I wait an hour top up coolant and with in 2 miles driving quite A roads at 55 mph things are getting to warm, I turn around and head home, a mile later temp gauge is 3/4 and oil temperature at 100oC (normally 90). I get home temp gauge towards red, oil temp 110oC I switch the engine off and hear gurgling from expansion tank hose.

History…
 New head gasket 6 months ago after white smoke from exhaust.
 Water pump propeller feels good when changing the thermostat and only a couple of years old.
 Not foam/mayo in the oil or underneath the filter cap.
 Coolant seems alright and smells like coolant to me.

 I’d been driving the for a good 45 minutes before things got hot under the bonnet and steam was spotted…

What’s my next move?  

hydrocarbon test to rule out worst case scenario

Are the rubber rad hoses getting rock hard like they are being pressurised from blown head gasket/cracked head?

Bad t-stat, or blown head gasket.  The t-stat is easier to replace, when you replace it I would flush and back flush the whole coolant system with the t-stat out.

see my how to in the archive section click the link on my signature line.

But prior to starting any work, turn the car on and get it running.  Squeeze the Radiator hose while you rev the engine to about 2K rpm.  If the upper hoses balloon and are hard to squeeze then you may have blown a head gasket.

Look at the Water pump Pulley as you are taking out the t-stat for signs of leakage under the back side of the pulley, if you have a UV penlight torch use it to look for florescence under side of the pulley, if that is the case and you see green glow (if using the green coolant ) then your Water pump is probably leaking at the seal, and needs to be replaced, just get the whole pump and housing (30mm hub).

let us know.

Quick update as I've not really touched the car as busy weekend…
Tried the latex glove sealed on the expansion tank filler trick and the glove did not inflate even after 45 seconds at 3,500 rpm from cold.

Tired another filler cap from my Mk1 Scirocco and took the car out for a 8 mile drive and engine still just off the red and oil temperature at 115 oC after the short journey on A roads with very little stopping and average 50mph.

Still gurgling sound when switching engine off and radiator hose may be harder than normal.

Ordered head gasket test kit so will try that when it arrives but I do recon I'll be pulling the head of again and fitting another new head gasket…  

Hey just something to remember......when you are checking your coolant system, ie pump etc.....you are assuming if pump is good thej you have good flow. Which is not necessarily the case. When I rebuilt my engine I cleaned all the galleries in the head and also the water jacket on the engine. Pulled one small silicone glob from inside the head and also two LARGE silicone rings. Which had me baffled for all of two minutes. But looked like whenever it had coolant flanges, or whatever changed out at sometime, there must have been a small leak so whoever repaired it slapped on a heap of silicone gasket sealer and the bolted the flanges back on. I guess once they did that the excess gasket sealer was then pinched off and free to float around inside the engine. So my point is all your hardware "might" be good but you may have a blockage in your head from a similar type situation.

Update,



Head gasket test kit, warm engine, 4 mins then boiling coolant shoots out.



Tried again with cold engine and liquid stayed blue.




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Waited till cool then checked coolant flow into expansion tank which was a trickle and did not increase with engine revs.

I removed the thermostat and drive belt to find I could stop the water pump propeller with my finger and still turn the pulley.

Water pump is genuine VW Brazil and only 6 years old.








VW cost cutting plastic parts had failed… the pump they replaced (original part) lasted 270,000 miles and 28 years with metal parts.





New 1/2 pump from Euro car parts later, the plastic thermostat housing seems to have warped from the heat…
New one on order.







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Got there in the end, hope no permanent damage done. Plastic should have no part of a cars running gear or even its door handles etc.

My daily driver fester has failed once in 85,000 miles. The plastic thermostat housing (replaced under warrenty)

Keep an eye on the Breakers, occasionally they get a older Golf/passat/jetta that has the metal outlets.

They don't warp. Keep an eye out on EBAY and Amazon.

Have you checked the radiator?  If its blocked or partially blocked, it will give over heating issues.

Disconnect the top and bottom hose, stick a hose pipe in the top and run it flat out, all the water should empty it of the bottom without coming out of the top (i.e. flowing at full capacity).

If it is the rad, and it's full of crud ( like mine was ) it might be worth running a flush through the system.

One good thing about the daily drive being off the road, I’m driving my other car this week as still waiting for parts.

Neighbour away so also using there drive.




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