Coolant leak after replacing thermostat

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Coolant leak after replacing thermostat

Postby Varlic » Fri 25.10.2019, 19:09

Hey All - I am newbie Elan owner having recently bought M100 ELA.

One of the issues I wanted to tackle was that the engine seemed to run cold (1/4 way up the gauge) when moving at motorway speeds. Figures this was because the thermostat was faulty in the open position.

Bought a new thermostat and followed the instructions on this forum to replace it. All seemed to be going smoothly, but after reattaching everything and refilling the coolant there was a serious leak from around the thermostat housing. I've disassembled everything again, sanded down the parts (again) to make sure they're mirror smooth, added gasket sealant too... the leak is reduced but is still there.

Anyone got any tips so that I don't have to take it to the repair shop?

Thanks in advance!
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Re: Coolant leak after replacing thermostat

Postby dapinky » Fri 25.10.2019, 20:46

Hi and welcome to LEC.

First, all Elans only go to the 1/4 mark at normal running temperature - it is just the way that the sender and guage interact (non-linear). When stuck in traffic (or otherwise stationary) it will go up to 3/4 before the fans kick in, then drop to about halway before they go off again.... returning to 1/4 once normal driving is reumed. It can be a bit disconcerting the first time watching the needle rise quickly and expecting the fans to kick in - and once they do, a huge relief!

As for the leak you now have, all I can suggest is that you ensure that the bolts are scrupulously clean (the threads can suffer some corrosion build up due to the different materials for the housing and bolt), and that they are going far enough into the head to pull the housing tightly enough to seal before bottoming out..... maybe try fitting an extra washer under the bolt head to see if it pulls it down better, and be carefull to ensure that you don't overtighten it and strip the threads in the head.
Dave

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Re: Coolant leak after replacing thermostat

Postby Varlic » Fri 25.10.2019, 22:19

Yeah, I now realise that there was no fault. D’oh.

The bolts appear to be tight, and I’m conscious not to over tighten. Will clean the bolts and try a washer.

Cheers,
Mark
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Re: Coolant leak after replacing thermostat

Postby Simon_P » Sat 26.10.2019, 00:49

Varlic wrote:added gasket sealant too...
just sealant or gasket plus sealant?

As it is mounted vertically the thermostat can drop out of the recess as you do the housing up and get pinched in between.

Have you traced the leak exactly?
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Re: Coolant leak after replacing thermostat

Postby Varlic » Sat 26.10.2019, 11:23

Hi,

Gasket + sealant.

It is hard to trace the leak exactly due to lack of space, but it certainly appears to be coming from the thermostat housing. The main radiator hose is dry and I can't think which other hoses I could have disturbed. If there are other water bearing hoses nearby then please advise and I'll check them out.

I'm not sure my technique for tightening the bolts was good. For example, I didn't turn each screw a bit at a time until they were both tight. For a cylinder head gasket I know this is required, but not sure if it is required for this job too. Please advise.

Also, I am not sure how tight the bolts need to be and I'm worried about damaging the head. Any guidance on the required tightness would be great too.

Thanks all!
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Re: Coolant leak after replacing thermostat

Postby Simon_P » Sat 26.10.2019, 13:37

Not tight! I do them up evenly and just pinch them up at the end with a 1/4 drive socket, being tighter is of no benefit. The gasket should be enough on its own so with sealant as well it shouldn't leak... unless the thermostat has slipped down.

The thermostat housing is prone to crack if the coolant temperature sensor is overtightened - see wiki for CTS. You will see a hairline crack at the thinnest point of the cutout on the top side of the the housing.
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Re: Coolant leak after replacing thermostat

Postby Varlic » Sat 26.10.2019, 18:38

Thanks for the input.

Tomorrow, I am going to try to remove and clean the bolts. Check that the thermostat is properly in its place. Example the housing for hairline cracks (although I think the leak is from the underside, suggestion the pinched thermostat). Tighten the bolts evenly and not overly tight.

All that, while trying to keep my fingers crossed.

Will let you know how it goes.
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Re: Coolant leak after replacing thermostat

Postby Simon_P » Sat 26.10.2019, 22:11

Just a thought - do you have the right bolts in the right place if the shank is too long the thread will bottom out before any clamping force is applied.
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Re: Coolant leak after replacing thermostat

Postby Varlic » Sun 27.10.2019, 13:44

There were only two bolts removed from the housing and they appear to be the same length. Will double check.
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Re: Coolant leak after replacing thermostat

Postby Varlic » Sun 27.10.2019, 20:27

Update...

Simon, you were right, the thermostat had slipped down and was being pinched between the thermostat housing and the head. There was an impression of the thermostat in the gasket so it was really conclusive.

I've removed it all, given the bolts a nice clean, applied gasket + sealant again and tightened it all up evenly. And... so far... no coolant leaks! :D

Thanks to both of you for your help and support with this.

Cheers,
Mark
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