Overheating After Replacing Expansion Tank & Sensor

[ian010778 21]

Hi all,

 

I've got a new issue with my 1.6 in that it seems to be overheating due to the radiator fan not coming on but it doesn’t ‘feel’ that warm.

 

About 12 months ago I put a new radiator fan switch in and it worked fine but due to finances has been sitting in the radiator without being started since.

 

Now I've started to finish the car I had to replace the expansion tank as I managed to break the original where the thinner hose goes onto the top of it to the left of the temp sensor (don't ask).

 

Also, whilst replacing the tank and seeing as I had the system drained I fitted a brand new ECU coolant sensor (from GSF) as I was experiencing some erratic idling the last time the car was on the road and I want to do a belt and braces job in preparation for MOT on April 23rd. So in real terms, since this time last year when the cooling system was working fine I've replaced the expansion tank and ECU coolant sensor.

 

However, when I started the car a couple of weekends ago it seemed to get warm (the dashboard gauge went to about 1/3 of the way around) but the radiator fan didn't cut in. Next thing I know there's what seemed to be hot coolant spraying out from around the expansion tank cap and the joints where the bottom radiator hose meets the metal pipe next to the o/s front wheel and the main/large hose on the bottom of the expansion tank had burst and were leaking.

 

When this happened, the dash gauge did not go much further up and no warning lights came on. Now I have experienced an overheat in the distant past on the way to Leeds in 2005 so I know that, looking at the temperature gauge, it was barely over normal operating temperature and the fan should really have only been on half speed, if on at all but no sign of it coming on even though the expansion cap and bursts joints told a different story.

 

I initially concluded that I may have an airlock that was both over-pressurising the part of the system where the joints had burst and was also stopping the hot coolant getting up to the fan switch so I drained the system, re-tightened the jubilee clips and re-filled very carefully whilst making sure the prescribed (by Haynes) 6.5 litres went in. This didn't solve the problem so I then concluded that the radiator fan switch that I fitted last year didn't like sitting doing nothing for twelve months so I ordered another new one from GSF. I then checked all the wiring (the actual wiring, not just the test plugs) and that's all fine (fan comes on at both speeds using my bit of testing wire), I drained the coolant, replaced the fan switch and re-filled (again following the correct bleeding procedure and putting back in what I took out after catching it in a clean bowl and making sure there was no crap in it!).

 

However, the car is still doing the same thing.

 

I started it again tonight and it gets warm after about what seems to be 6 or 7 minutes (according to the dashboard gauge) but then starts hissing from the expansion cap. However I got a bit brave tonight and started looking/feeling around as it warmed up and started to hiss and although the radiator and pipes get warm I can comfortably touch them whilst the engine's running, even at the point where I can start to hear the hissing from the expansion tank cap.

 

IIRC, the first fan speed comes on at about 82 degrees and even at this temperature the engine wouldn’t be in an overheat situation. In my mind, I shouldn’t be able to touch the pipes and radiator with coolant at 82 degrees but I can. This tells me that the coolant in the system isn’t actually that warm (as I can touch stuff, the dashboard gauge that has always been reliable in the past isn’t overly high and the radiator fan hasn’t come on even with the new switch installed) but there’s still what appears to be steam coming out from around the expansion tank cap. However I don’t understand how this can be steam if it’s still not too hot to touch (below 50 degrees if I remember my GCSE science correctly). Sorry, I haven’t articulated that too well but basically it looks as though it’s over heating but I don’t see how it can be as I can still touch everything so it can’t be that warm.

 

I’m really at a loss now as I think I’ve eliminated everything (fan switch, air lock, wiring etc.) and I don’t know what to try next.

I have just spent an hour or so reading up on the forum about cooling systems and the only thing I can think is that the expansion tank cap isn’t sealing properly but this is the original cap that has always worked and worked last March too. The replacement expansion tank did come with a cap but it looked a bit manky and my original cap has always been fine – also I’m not convinced that a poorly sealed cap could create the issues I’m experiencing.

 

All I’ve really done since the cooling system last worked is changed the expansion tank and the ECU coolant sensor so I’m really baffled by this.

 

Sorry this is a really long post but I thought it important to get all the info’ in here as I can’t find any posts here about similar issues (using forum and Google searches) and (I think) I’ve been really meticulous and methodical when trying to sort this out.

 

Whilst I’ve been writing I am thinking that if the cap isn’t sealing and pressurising the system correctly then what I am perceiving to be steam may just be pressurised coolant escaping and as the pressure is escaping this may be stopping the coolant from circulating properly and therefore I’ll be getting an uneven temperature at various points in the system – does this sound like a feasible explanation to my issue?

 

Any suggestions or opinions on whether the expansion cap could be the cause or whether I’ve over-looked something else would be really appreciated please.

 

I am sorry this is so long and if anyone has got to the end I really do appreciate you taking the time to read this.

 

 

Ian.

[205kenny 7]

Sorry, i may have missed some important imformation as i'v only skim read your post.

 

When you bled the system are you sure you opened each bleed point? and have you check if your thermostat is opening correctly? blocked radiator?

 

If your confident its none of the above, it could well be a blown head gasket causing you system to pressurise.

Edited March 22, 2012 by 205kenny

[DamirGTI 342]

C/P :

 

when you switch the engine off it's up to the sealed pressurized system to hold the coolant beneath the boiling point , so , if you've a crack on the bottle , a bad/leaky bottle pressure cap , leaky hoses etc. localized boiling will occur inside the engine creating steam pockets which will cause metal warping/cracking as a outcome .. HG sealing issues as well

 

Replace the expansion bottle cap ASAP , especially if you can hear it hissing that one is long gone .. it'll allow the coolant to heat up over the boiling point after switching the engine and it'll damage the engine .. (i had one time cracked liner , and another time blown HG all because of leaky expansion bottle cap ..)

And do not use coolant temp. gauge as a reference , it reads the temp. on the thermostat housing .. coolant temp. will be much higher at other internal areas such as around the cylinders , valve seats etc.

 

Damir

Edited March 23, 2012 by DamirGTI

[pugdamo 111 2 Cars]

As above.

I would try to get it to a garage and see if they can carry out a block test on it,at least then you will know whether it is head gasket,these tests are pretty quick and a garage shouldnt charge you to much either.

[ian010778 21]

Cheers all,

 

Hopefully it's not the HG - not sure I'd be confident doing that but I'll be reading up in preparation . If it is the HG, would I also see other symptoms (water in oil etc.)? Just asking as I can't get it to a garage easily (not road legal at the mo') and just trying to eliminate the HG before I go messing about with it. Obviously this is the last thing I want to be doing and I want to eliminate everything else first but if I can easily rule out the HG then I'd be very happy.

 

I'm going to swap the expansion cap for the one that came with the replacement header tank and I will fully drain the system, flush it all out with a hosepipe and re-fill ensuring I use both the bleed points over the weekend.

 

Whilst the system's empty is there anything else I should be checking? Kenny, how do I test the thermostat opening correctly please and I also thought that I might be wise to test the water pump but I'm not sure where it is and/or how to test it?

 

Does this sound like a sensible plan in order to rule everything out apart from the HG?

 

Again, many thanks for taking the time to read and respond.

 

 

Ian.

[Tom Fenton 1,542]

For it to be blowing hoses off something is definitely not right. From cold get an assistant to start it up whilst you have hold of the top rad hose and are squeezing it tightly. If the hose gets very hard with pressure almost straight away with the engine running then you have either head gasket or liner seal problems.

[ian010778 21]

Thanks Tom, can I just confirm that the top hose is the larger diameter one that goes into the radiator above the fan switch please?

 

If so, I did have a good squeeze of the hoses last night (including this one) following a few minutes of running after a cold start. It seemed to be quite flexible and was easy to squeeze (no harder than when it's cold) but I will get the wife to help Saturday morning so I can gauge how the pressure is building in this hose from starting up.

 

Should all of the hoses stay reasonably flexible and squeazable regardless of the temperature as the car is running?

 

 

Ian.

[205kenny 7]

Cheers all,

 

Hopefully it's not the HG - not sure I'd be confident doing that but I'll be reading up in preparation . If it is the HG, would I also see other symptoms (water in oil etc.)? Just asking as I can't get it to a garage easily (not road legal at the mo') and just trying to eliminate the HG before I go messing about with it. Obviously this is the last thing I want to be doing and I want to eliminate everything else first but if I can easily rule out the HG then I'd be very happy.

 

I'm going to swap the expansion cap for the one that came with the replacement header tank and I will fully drain the system, flush it all out with a hosepipe and re-fill ensuring I use both the bleed points over the weekend.

 

Whilst the system's empty is there anything else I should be checking? Kenny, how do I test the thermostat opening correctly please and I also thought that I might be wise to test the water pump but I'm not sure where it is and/or how to test it?

 

Does this sound like a sensible plan in order to rule everything out apart from the HG?

 

Again, many thanks for taking the time to read and respond.

 

 

Ian.

 

Condensation from exhaust, using coolant, mayo in oil, rough running,low cylinder compression, pressurising coolant are all things that can be affected by a blown head gasket. However the car probably won't have all these symtoms and can sometimes be difficult to diagnose. I guess it depends which part of the gasket has failed. As above though best way to test is to have it block tested.

 

To check thermostat, check to pipe coming from the thermostat is getting warm when up to tempreture. You can also test them by removing them and putting them in boiling water, then checking the theromstat has opened.

[ian010778 21]

Thanks Kenny,

 

I'll update this post tomorrow with any progress

[ian010778 21]

Hey guys,

 

I think I've made some progress today. I noticed when I drained the system this morning that when I started to remove the air pipes and the AFM that the rate of coolant coming out increased a lot so I think I may have trapped one of the coolant pipes the last time I put it back together which was after cleaning the throttle body.

 

I drained and flushed the cooling system, got and fitted a new thermostat from Halfrauds and put everything back together very carefully, making sure I haven't trapped anything. Then re-filled very slowly, using a header tank and making sure the bleeds ran with clear coolant before doing them up (thermostat first, then the one near the firewall).

 

I've just started the car and she seems to run really well, idling well and she sounds really smooth with no misfiring so I'm hoping the HG's still ok but I will get the block tested when the garage has it for MOT.

 

However, I now daren't leave her running too long in case I haven't solved my problem and I damage the engine so after only a few minutes I switched her off and had a good look/feel around - results as follows: -

• There was a little bit of steaming from around the thermostat housing but this is because I'd got it a bit wet earlier
  
• The coolant in the expansion bottle was quite warm to touch, as was the smaller diameter pipe to the right of the expansion cap (that goes along the top of the radiator)
  
• The top radiator pipe (big one from thermostat to radiator was cold and so was the radiator itself) this is probably because I didn't run it long enough for the thermostat to open
  
• The pipe that runs from the bottom of the throttle body back to the top of the expansion tank was cold
  
• The in-car heater started blowing hot nice and quick as usual
  

Now, given my comments about removing the air pipes affecting the coolant drain speed and also that the throttle body return pipe to the expansion tank stayed cold when running could I have put the two coolant pipes on the bottom of the throttle body on the wrong way around after cleaning it?

 

If so, would this matter? I do seem to remember not being sure which way around these went after cleaning the TB but I decided they were probably connected and it wouldn't matter

 

Any thoughts would be gratefully received.

 

Cheers all

 

 

 

Ian.

[ian010778 21]

Howdy - quick update.

 

All seems fine now, I spent the last couple of nights going over the cooling system and making sure everything flowed well.

 

After checking a really useful diagram of the pipework I did have the TB cooling pipes on the wrong way around so I rectified that and started her up this evening.

 

After about 15 minutes of idling in the garage there was no sign of over-pressurising and the radiator fan cut in and out correctly so, fingers crossed she's ok.

 

I've now got a compression tester and a block testing kit so will be checking the HG at the weekend.

 

Thanks all for the help - as always, I would have given up by now if it wasn't for this forum!

 

 

Ian.