Technical Help ! Water blowing out expansion tank cap !

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Technical Help ! Water blowing out expansion tank cap !

smitch

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Help ! At the end of my journey to work this morning, when pulling off the motorway (uneventful 30 mile journey, cruising at 70ish. I noticed the temp gauge was slightly above normal (indicating just over 90 rather than just below). Then a few wisps of steam out the bonnet when I stopped at traffic lights, temp gauge rising very slightly, so I whacked the heater and fan on full, which only put out intermittent warm/cool air rather than the expected blast of scorching air but the temp gauge did fall back to normal. I nursed it a couple of miles to my work car park, temp gauge didn’t climb any more. Opened the bonnet, coolant has been leaking out the expansion bottle cap and steaming where it hits hot engine parts.

I slowly undid the expansion cap, there was pressure in the system and some more coolant bubbled up and out, then stopped. It was hot but not enough to burn/scald me. Also the rocker cover was hot to the touch but no more than I’d expect. So I cautiously started the engine , expansion cap off (temp gauge still showing normal), the water level in the expansion tank dropped, then after a few seconds rose up and bubbled over, so I switched off the engine again. It had started normally, idle seemed to be smooth and normal and there’s no sign of water or steam out the exhaust.

What are my options here – Coolant leak somewhere, level too low, causing steam generation in the head and excessive pressure ? Or head gasket gone ?


What are my best options to get home (30 miles) and deeper investigation tonight if I can get back. Should I top up the water, and take it for a short test derive at lunchtime, or go get some radweld ?


Also I happen to have a cylinder compression tester in my tool box in the car as I’ve been meaning to check it as a matter of interest, I’ve only had the car 6 weeks. How would I detect a cylinder to water leak with a compression tester ?

Car details - R reg cento sporting, bog standard, running great, 80Kmiles. Had the head gasket done by the PO (£750 garage bill) about 10000 miles ago, along with a new rad and thermostat.
 
Was the rad fan kicking in?

Could be that the thermostat is stuck. Or that the HG has gone again.

With the engine cold, remove cap, start engine. If you see bubbles then it's game over. (Bubbles are the exhaust/combustion gasses getting into the cooling system)
 
Hi

Do not run the engine when it is hot or may have lost coolant, unless you like head gasket kits... Instead let it cool (30mins plus) and top up when cold. The temperature gauge does not necessarily indicate coolant temperature if it is in air.

Buy some coolant at lunch time and top up cold and bleed cold.

Limp home (i.e 50 mph) stop after five miles and let car cool off. Run the heater on hot and the fan on full al the way home, if the air gett cool pull over and let the coolant cool off and rebleed.

The fan should have been on during the way to work, if it was not you need to fix the fan first...

If you have not ben maintaining the auto you need a proprietary rad flush kit.

Noel
 
Hi, I nipped back out to the car around 10 o’clock when it had cooled down, topped up the coolant took about about 1L until it started coming out the bleed screws. Couldn’t find any obvious leaks. Started the engine, expansion cap off, idle normal, No bubbles in expansion tank even when I revved the engine a bit by hand on the throttle cable input to the throttle body. So I screwed the cap back on, and let it warm up at idle. Kept checking the hoses for leaks and warm up. Everything seemed normal, heater hoses warmed up first, heater blew a normal amount of hot air, rad hoses warmed up Ok, temp indication was up to about 85c when water started leaking out the expansion bottle cap again, so I shut the engine off (the fan hadn’t kicked in yet but it was running this morning). I’m going to get a new expansion bottle cap at lunchtime and hope it’s as simple as that.
Would you expect the coolant to expand enough to overflow the expansion tank if the caps not sealing properly ?
Or is the head gasket kippered but only blowing into the coolant when hot ?
 
A new expansion bottle cap seems to have fixed it :D Test driven OK everything seems to be normal. I’ll still treat it easy going home. Many thanks for all your input and suggestions (y) I still need to get round to that compression test sometime.
 
Nice one.

Just double check that the fan is kicking when it should. I'd also bleed the cooling system (now that it is pressurising correctly). How much water have you added, make sure you've got the correct concentration of anti-freeze in there (just using water will provoke the HG over time)
 
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