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Post by charlie on Mar 18, 2019 11:17:49 GMT
Hi there!
Anyone know what could be causing my Austin to overheat? Recently had the radiator and coolant flushed and the thermostat replaced and still overheating. It’s fine at 90/100kmph - but as soon as I hit 60/70kmph the temp gage starts creeping. Once parked up at home the engine is fine to touch initially - give it about 10 or so minutes and it’s too hot to touch! Any ideas?
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Post by dave1800 on Mar 18, 2019 12:41:51 GMT
Hi Charlie
Difficult to diagnose from afar, but how hot is it where you are now? Is this a new problem or something that had developed over a period of time.
There are many possibilities but the following need to be checked.
Slipping fan belt
Ignition timing - retarded ignition will result in overheating
Mixture - as the car is overheating at idle check it is not too weak (try temporarily richening the mixture 1 complete turn to see if this improves the idle overheating, if so it gives a possible direction for further checks) , also check the float chamber for deposits that could restrict the flow of fuel
Radiator expansion tank pressure cap
Compression test to ensure the head gasket isn't leaking
You should also consider flushing the block if that wasn't done when the radiator was done it's amazing how much sludge can build up especially if the coolant (UK antifreeze!) isn't replenished.
regards
David
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Post by andrewa on Mar 18, 2019 14:13:16 GMT
Just to add to Dave's excellent list - duff thermostat - I had two in succession despite both being brand new.
Cheers
Andrew
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Post by snoopy11 on Mar 19, 2019 9:49:50 GMT
Before we get too deep into this one you mentioned that you have just had the radiator and tank flushed. Have they put the caps back correctly and are they sealed properly
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Post by charlie on Mar 20, 2019 2:53:13 GMT
Thanks for your response guys! All checks have been done for the head - and all results have come back negative. Besides hoses being replaced, radiator / coolant being flushed and the thermostat being replaced - the fan belt has been tightened and the ignition timing has been adjusted. All caps seem to be in place correctly. Have had someone suggest something might be loose in the water pump. Mechanics want to replace radiator? Does this seem too far fetched and should check mixture / water pump / anything else first?
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Post by dave1800 on Mar 20, 2019 4:29:28 GMT
It would help if you could confirm if this is a problem that has developed and if so was it sudden or gradual. ( a thermostat failure and maybe head gasket can be sudden and as Andrew noted he has had a dud replacement thermostat.) If the car is a more recent purchase was it present so the work you have had done was to rectify it.
I would not replace anything until a compression test has been completed to rule out / or in a head gasket failure it is a quick test. Are there any signs of water in the oil, oil in the water? The mixture check I described earlier and the and examining the float chamber only takes a few minutes and the latter should be a routine service check.
David
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Post by charlie on Mar 20, 2019 4:40:11 GMT
The problem has only just developed in the last month and has gradually become worse over the coming weeks. They’ve done a compression test and the head is in the clear. Nothing to indicate a problem there. Will check the mixture, the oil - water and the float chamber before replacing anything more. Might replace the thermostat again in case of a dud after other checks are complete and nothing is found.
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Post by charlie on Mar 20, 2019 4:41:25 GMT
..if nothing is found*
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Post by dave1800 on Mar 20, 2019 9:20:03 GMT
There are a few reports from MGB owners of failed water pump impellers either cracked or slipping - unfortunately only apparent on removal. It may be worth checking after the easier options if the problem isn't resolved. The overheating could be a weak mixture down to fuel starvation through a partial blockage in the carb float (greater effect at high speed /load) or an air leak somewhere in the inlet manifold and fittings including the PCV, brake servo and inlet manifold gasket which would have far less effect at higher engine speeds. I assume you have a MK1 engine with electric fuel pump, so that should either work or not but easy to check the flow. David The problem has only just developed in the last month and has gradually become worse over the coming weeks. They’ve done a compression test and the head is in the clear. Nothing to indicate a problem there. Will check the mixture, the oil - water and the float chamber before replacing anything more. Might replace the thermostat again in case of a dud after other checks are complete and nothing is found. |
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Post by charlie on Mar 20, 2019 9:31:12 GMT
I’ve just been out to check the oil and water - neither are where they’re not supposed to be. However I’ve turned the key and let the engine run for about 5mintues - the block / head were fine to touch but the lower radiator tank and the hose connecting from the tank to the block were burning hot. Coolant is leaking out from one of the bolts that connects the hose to the block. I’ve just come out after letting it sit for another five minutes not running, the lower radiator tank and hose are still burning hot and now the block / head has some heat in it too.
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Post by andrewa on Mar 20, 2019 13:06:16 GMT
My vote goes with either air lock somewhere in system and or a blockage/build up of crud somewhere, so i would start with a thorough flush of the radiator and the block.
There is a drain point for getting the stuff out of the bottom of the engine. I'll look up where it is if you like!
Then when all's clean and you've purged all the air out of the system you can move on from there.
Cheers
Andrew
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Post by charlie on Mar 21, 2019 0:21:43 GMT
That would be fantastic - thank you! Thanks for everyone’s help, just trying to figure out the best way to go about this - what to do / look at first. So with all that in mind, I’ll be looking over it properly on Saturday - so will take it from there!
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Post by dave1800 on Mar 21, 2019 2:18:30 GMT
The drain plug for the block is immediately below the oil pressure switch. Early engines had a brass tap which could have seized so be careful. Better to unbolt from the block if it feels seized. There can be so much crud that you need to poke something in the hole to get the flow started.
David
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Post by andrewa on Mar 21, 2019 14:27:41 GMT
Thanks for saving me a task David...just heading off to France in a mo to try 1800 at high speed on banked circuit!
As usual have packed kitchen sink to keep car going in event of failure and next to nothing for me!
Will report back on how it all went next week - hopefully with video and still photography.
Good luck with the flushing Charlie - hope it helps.
Cheers
Andrew
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Post by dave1800 on Mar 22, 2019 0:44:32 GMT
Will you be challenging this record 1800 Monza - scroll down 75% of page. Good luck! David ...just heading off to France in a mo to try 1800 at high speed on banked circuit! As usual have packed kitchen sink to keep car going in event of failure and next to nothing for me! Will report back on how it all went next week - hopefully with video and still photography.... Cheers Andrew |
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