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TR4 AJJ

Thermostat Issue ?

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Hi All,

 

My TR4A has developed a new thing, although its only happened twice in the past two weeks ( 250 miles ).

 

After starting and during the warm up period the temperature keeps going up past mid point where it normally sits to 3/4 on the gauge and then suddenly drops back to 1/4 on the gauge. It then continues to heat up to normal temperature and runs fine.

 

Both times under the bonnet is then a mess. The reserve bottle is full and there appears to have been an explosion of hot water from the rad cap all over the engine.

 

I lose just under a 1lt of coolant when it happens.

 

The rad cap is new and the correct one.

 

Im assuming that the thermostat is not opening quickly enough and causing this ? Unfortunately, we have just embarked on a road trip so I wont be able to sort till Im back. However, is this likely to be anything else that I could look at whilst away ?

 

Thanks for advice ..... again.

 

Andy

Edited by TR4 AJJ

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Hi Andy,

as you say it looks like the thermostat is not letting water through until it fully opens. There should be a small hole in the thermostat to allow a leakage path.

 

Make sure that the radiator is not full to the brim. Enough to cover the vertical vanes is fine.

Make sure that the expansion bottle is only 1/4 full, no more and that the end of the pipe reaches tpo the bottom of the bottle and has an obliquely cut end.

 

Roger

 

PS - just spotted Dave's post. Remove thermostat - easy to do by the roadside.

Edited by RogerH

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Thanks chaps,

 

Running without the thermostat - would the car run too hot ? I thought the engine needed the restriction of the stat to slow the flow down through the radiator. That said, we're only heading to northern France and Jersey Island, so I'm not expecting tropical heat ...

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Hi Andy,

it could run a little on the cool side and or take longer to get up to a good temp.

It will not be a problem for your journey.

 

roger

 

Thank you Roger - once again !

 

I shall tackle it this morning.

 

Andy.

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This time of year you will only notice it's a bit slower to warm up...I doubt you'll notice a difference once at running temp.

Certainly preferable to a blocked stat causing local hotspots and boiling...that might crack something expensive...

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This time of year you will only notice it's a bit slower to warm up...I doubt you'll notice a difference once at running temp.

Certainly preferable to a blocked stat causing local hotspots and boiling...that might crack something expensive...

 

Yes indeed ! My thoughts exactly ...oh, and i don't enjoy cleaning the engine bay every time either !

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Be careful if that alloy thermostat housing hasn't been touched for years..bolts may snap and the alloy may turn to mush...

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Hmmmm...

 

Well I have removed the thermostat, refilled the tank to just above the vanes and the expansion tank to 1/4 full.Once it was warmed up I took it out for a short drive (about 8 miles). The temperature gauge didn't really go much above about 75 degrees. It normally sits dead centre at 90 degrees so that seems all good. However, when i got it back, the expansion tank was full and over flowing slightly and it had started to escape from the tank cap by the looks of it too. There was coolant around the top. At no point did the gauge show it above 90 degrees, as it had in previous times.

Edited by TR4 AJJ

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My next guess would be the cap is not sitting or functioning correctly.

Its also a cheap check.

Can you borrow one from local group member.

Even off their car.

After that you could be into checking the temp gauge system. Kettle tests with sender etc.

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My next guess would be the cap is not sitting or functioning correctly.

Its also a cheap check.

Can you borrow one from local group member.

Even off their car.

After that you could be into checking the temp gauge system. Kettle tests with sender etc.

 

 

 

I changed the rad cap back in spring as I had the wrong one on then. I ordered this exact one (part 71) off Moss.

 

Even though it's filled up the expansion tank, it doesn't feel like its got too hot.

 

I'll be able to get my one off my Spitfire but I'n not sure if that's the right size, etc.

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Even though it's filled up the expansion tank, it doesn't feel like its got too hot.

 

etc.

Thats what makes me question the cap / seal.

 

The gauge temps werent a lot

Thus I suspect neither were the pressures.

 

Yet the coolant is getting past the sprung seal into the bottle.

 

It is not a 4lb cap is it ? Thus too low.

 

They need to be the right pressure and the right depth. is it long /deep enough to seal ?

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Thats what makes me question the cap / seal.

 

The gauge temps werent a lot

Thus I suspect neither were the pressures.

 

Yet the coolant is getting past the sprung seal into the bottle.

 

It is not a 4lb cap is it ? Thus too low.

 

They need to be the right pressure and the right depth. is it long /deep enough to seal ?

 

It's a 7lb cap and it was ordered off Moss as the correct one.

 

Yesterday I did 130 mile trip, all at an average of 60-70 MPH (M25 / A3). It was running great. it was after it had cooled down on the ferry trip that I noticed the stat had got stuck and temperature went high momentarily (as described in first post).

 

Today, it didn't even go high but still filled up the expansion tank. I will take a look at the cap and make sure there's nothing obviously wrong with it.

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Is the best way to get rid of that to run it with the rad cap off ? The thermostat is out now so I assume the air would find its way out with cap off ?

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Hi,

 

I now feel the issue might be more serious...

 

In an attempt to get any air block out, I ran the car with the cap off up to temperature. It ran fine and once hot I took it for a run of about 12 miles. Unfortunately, nothing changed and it filled up the expansion tank again and was starting to come out the rad cap too.

 

The more worrying thing is once I took the cap off and all around the top of the expansion tank, is foam.

 

Im worried its a head gasket or worse now ...

 

Theres no sign of issue in the oil from under oil cap or dipstick.

 

All said, the car seems to run fine and doesnt over heat.post-15231-0-92136100-1536696421_thumb.jpeg

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Hi Andy,

that could make sense. Contact your local garage - they can do a leak test by detecting gases in the coolant.

 

Roger

 

Ok, thanks.

 

Is the most likely result blown head gasket ? Or worse ...

 

The engine was only rebuilt in 2011 ....

Edited by TR4 AJJ

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Who could know until more diagnosis takes place.

 

one step at a time.

 

Roger

Ok, thanks for all the advice Roger. I’ve already made enquiries with friend / local garage.

 

Guess it’s not going on to France tomorrow now though ... :(

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I bought a tester like this a couple years ago.

BT-3 BLOCK COMBUSTION LEAK TESTER KIT CO2 BLOCK HEAD GASKET TEST FLUID 35bb https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F273245490361

 

 

Ruled out a problem on a v8 I used to have.

Good job as it wouldnt identify which bank.

 

But did identify my TR3a head gasket issue.

 

Sorry about your trip though Andy

 

H

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Thanks H,

 

Ill most likely use a local classic car garage to diagnose the issue and then decide where to go from there.

 

Still going on the trip though !! Have to decide in the next few hours .... Spitfire Mk3 ..... or dull & boring Volvo

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