Hi, any help would be much appreciated!!
My astra started overheating......turned out the rad fan wasn't kicking in. With the radiator switch bypassed the fan works fine....I'm still waiting for new switch.
With the fan always on it worked fine for a few weeks and didn't overheat......until now!
Suddenly it's started overheating again even though the fan is always on...?
I thought it might be an airlock....so I was advised to remove the expansion tank cap and let the engine idle without revving.
I did that and this happened:
* Air bubbles came up in the tank, and the level went down.
* After few mins therostat must have opened
* Expansion tank suddenly overflowed with hot water and dribbled out all over engine
* Turned ignition off
* Topped up with water
* Put cap back on and idled it again for a few minutes
* Temperature went up nearly to the red again
* Let it cool down for a bit then idled again with fan disconnected until approaching red again
* Radiator hot at top and bottom, and hoses hot.
Seems like the coolant IS circulating, guess thats why coolant overflowed suddenly with cap open.
So I'm stumped, as far as I can see the fan, thermostat, pump and airlock situation is ok, but it definitely overheats, it bubbles and sounds like it's boiling if allowed to get right up to the red.
Anyone got any ideas how to solve this problem?
Edited by Dynamic Dave on 19/01/2008 at 12:26
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Either the stat is faulty or you have ahead gasket problem. For the latter let the engine cool right downundo and then do up the header tank cap. Start the car and run it at 2000rpm for 30 seconds, turn it off. carefully undo the rad header tank cap and establish that the tanks has not pressurised. If the hoses are firm and the tank is pressurised then you need to go and get a capable garage to 'Sniff the header tank for signs of combustion gases. Regards Peter
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Could be head gasket.
Could also be sticking thermostat, but its sat behind timing belt so not easy to test/change.
Could also be water pump, (there have been problems with impellors breaking up etc) but again its a timing belt off job to do.
Could also be a blocked/poor radiator, try flushing it thouroughly and see if it makes any difference.
Agree get a sniff test done, or if you are diy capable try water pump, thermostat, timing belt and see ? Could remove spark plugs and see if 1 is totallydifferent colour to other 3? May give clue to water/compression mixing problem?
hth
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Thanks for the advice, I'll look into those...
I don't think the stat is sticking because the radiator does get hot...
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Thanks for the advice, I tried that for 30 seconds but there was very little pressure in the expansion tank when I released the lid...
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Everything points to little, or no, circulation. I'd try a new stat first.
The rad fan won't come on if hot water isn't reaching the temp switch in the rad.
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What makes you conclude that it's overheating? Is it the temperature gauge reading (which could be wildly inaccurate) or is the coolant actually boiling and coming out via the cap overflow?
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I haven't seen the coolant coming out of the overflow, but the engine gets very hot and starts making boiling noises and steam has actually come out from under the bonnet one time...
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Thanks for that I'll check it out. I think the stat must be ok though as the radiator heats up therefore must get coolant from the engine..??!?
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>>Pump??
Yes, it's beginning to look that way.
As its a cam belt off job, it will need a new belt, and might as well put a new thermostat in while the belt's off.
Do these have a seperate sprung tensioner too? (Off the top of my head, I can't remember when they were introduced) If so, I would probably also put a new one in.
Number_Cruncher
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Thanks for the responses!
Just to check before buying any parts...
If the pump has failed in some way is it still possible (with the cap removed) for the hot water to get to the radiator and then overflow up through the expansion tank..??
Or could the overflow have been caused by the water boiling and expanding then backing up to the tank directly from the engine..??
I'm a bit of a novice with engines so I'm still confused by the symptoms.
Thanks!
p.s. I checked the expansion tank for oil earlier, none can be seen, and there is no mayo on the oil cap....
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I would bet there is a problem with the water pump not circulating coolant. If it's the original pump from 1993 then more than likely. As it's a big job you need to take off the timing belt and whilst doing that replace with a new belt and tensioner, put new water pump in and also change the thermostat plust take off the engine mounting to get to it all it's worth making a good job of it. Then you know it's all done and shouldn't give you any problems for several years. Depends if you want to keep the car long term and if no other problems like rust or engine issues it's worth investing in it. Better the devil you know etc. Either way it may wreck the head gasket if it keeps overheating and then you are into an even bigger job and bills. If you decide to renew the water pump, timing belt and thermostat I would flush the radiator out whilst coolant is drained to eliminate that before re-filling with some decent antifreeze 50/50 solution.
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Thanks for the advice....I'll try what you have suggested
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