Coolant temp problems - Confirmed HGF

steve_weegie · Post by **steve_weegie** » Sat Jan 19, 2008 5:32 pm

My car seems to have developed a worrying coolant problem. It first came to light a couple of weeks ago when coming to the end of a motorway.

Temp was stable at 87 on the motorway, then shot up to 110 when slowing down for a roundabout. This now happens everytime

I left the car idling and the temp was sitting at 90 but the return hose from the radiator was cold. Temp gradulaly rose to 100, fan cut in, but temp still kept going up. As soon as i gave it some revs, the temp shot down to 91 almost immediatly.

Could this be a sticky thermostat?
Air lock in the system?
Broken water pump?
or somthing else?

I tried bleeding the system quickly at doms today and only coolant came out both bleed screws with an engine temp of 90.

Anyone got any ideas of how i'd go about solving this? It's an S2 k series with 67k on the clock...

Cheers,

Steve

robin · Post by **robin** » Sat Jan 19, 2008 5:39 pm

Airlock in the system:

* Head gasket failure causing gassing into coolant - get it tested for hydrocarbons in the coolant - IIRC mac has the sniffer?

* Less serious would be a leak, e.g. inlet manifold gasket.

* Less serious again would be faulty coolant tank cap allowing the coolant to boil and thus introduce vapour lock when hot.

Thermostats almost always fail safe, i.e. the engine will run cold when cruising on motorway.

Water pump unlikely to fail in such a binary fashion.

Do a sniffer and compression test ASAP.

Remove all four spark plugs and see if any is shiny clean - if it is, then your leaking coolant into that bore one way or another.

Cheers,
Robin

Rich H · Post by **Rich H** » Sat Jan 19, 2008 5:55 pm

^+1

What he said. Start with the plugs and check the expansion tank for dribbles of coolant on the outside. Will diagnose inlet manifold gasket or tank cap PDQ.

Fingers crossed its the cap. Change it anyway...

Edin430 · Post by **Edin430** » Sun Jan 20, 2008 12:20 am

sensor?

Victor Meldrew · Post by **Victor Meldrew** » Sun Jan 20, 2008 12:41 am

Me too.... any chance Mac will be coming along on Sunday? with the sniffer.....

They cant be that expensive are they for a sniffer?

steve_weegie · Post by **steve_weegie** » Sun Jan 20, 2008 2:36 am

Cheers for all the advice guys.

Ali from sls went above and beyond the call of duty and had a look at it for me at short notice.

He bled out some coolant from the radiator and it seems to have stabilised a good bit - I'll know more after a run tomorrow, but the temp settles to high 90's coming off the motorway and that's a big improvment.

Quite how the system got air in it is another question however and I'll be taking robins advice asap. If there a sniffer around that I could borrow, it would be immensely helpfull! Needing head work on the engine will totally scupper any chances of european fun!

Cheers,

Steve

mac · Post by **mac** » Sun Jan 20, 2008 7:53 am

I've got the sniffer - but I'm working today I'm afraid.

Steve, you can pop round anytime this week (except Tuesday) as it only takes 5 mins.

John, Same goes for you but it's a bit more of a trek - or just give me a prod the next time there's an elise event.

Mac

robin · Post by **robin** » Sun Jan 20, 2008 10:41 am

Steve - when's the last time you had any work done on your car that might have affected the coolant system? If it's a long time ago, you must have a lproblem of some sort - the air in the coolant system is just a symptom, not the cause

Cheers,
Robin

steve_weegie · Post by **steve_weegie** » Sun Jan 20, 2008 8:52 pm

Mac, Id seriously like to come across on tuesday but am in st andrews all this week. The earliest i could get across would be the weekend

Robin, its been over a year since any work was done on the cooling system, so I completely agree that somthing is a miss somewhere.

The engine has never been apart to date, there's no water vapour from the exhaust and the coolant level drops slightly when some revs are applied. From this, I'd guess the inlet manifold is ok and that the fire rings werent leaking gas into the coolant, but I really need to get this checked ASAP. Ali also mentioned that the tank pressure wasnt excessive, which cheered me up for a bit

What's interesting from todays run is that when the temperature shot up, the heater would go cold... Give it some revs and the temp would go down and heater would start working again. After my first unscheduled pitstop, David witnessed bucketloads of water return to the expansion chamber when i gave the engine some beans so there's definatly air (and quite a bit) in the system. Where its coming from is beyond me at the moment

Cheers for the help,

Steve

steve_weegie · Post by **steve_weegie** » Sun Jan 20, 2008 11:30 pm

Ok, instead of reading seloc and worrying about HGF I decided to be mildly constructive and check the plugs. Happily they all look fine.

I'm begining to wonder if its the heater matrix thats the problem though. When i turned the fan on the other day, the windscreen was clear but started to fog up where the vents hit it. I put this down to moisture in the air, but i suppose it could be a very small leak? I've not been loosing a noticable ammount of coolant but did top it up about a month ago before any problems started.

Mac - I'm not going to stay at st andrews tomorrow night in light of this. Is there any chance i can pop over and do the sniffer test?

Cheers,

Steve

Victor Meldrew · Post by **Victor Meldrew** » Mon Jan 21, 2008 12:09 am

Heater matrix? Now there's a thing. I can't seem to keep the inside of my screen clean, keep getting a build up of gunk on it. Wonder if its coolant depositing itself on the inside of the screen.

We did a compression test on mine today and it was all fine. It showed 13,13,13,13.5. All in the green. The theory being that if there was HGf it would show up as a drop in compression. Thank Jonathon.

What pressure should the system be running at? I was toying with the idea of fitting a pressure gauge in the system. I know the header cap is spewing coolant put I don't know what pressure it is designed to lift at. Its one thing to have a faulty cap, totaly different to have a true overpressure.

also strange thing happened. I commited the cardinal sin of putting a small tub of rad weld into the thing to see if it would help.
Previously the car would run with 84-86 deg on the gauge on a steady run. After a few miles the steady temp dropped to 78-79 deg and stayed much more stable after giving it some serious spanking on the way home. Still spat out coolant out of the expansion cap when I stopped so I don't know yet if the cap is xxxxe or if there is still another problem.

Need to get a hold of the sniffer..... Don't suppose Ken could borrow it and bring it to Noop's on Saturday? Just a thought.

steve_weegie · Post by **steve_weegie** » Mon Jan 21, 2008 12:26 am

If it's the matrix leaking (could very well be by the sounds of things....) then you'll probably still have air in the system that'll need bleeding out. I'm going to see if i can pop round to Mac's tomorrow (fingers crossed) and use the sniffer.

You'd need about 15psi of pressure to keep water from boiling at 120 deg. This is pure theory though - will probably be different with coolant in the mix....

fd · Post by fd » Mon Jan 21, 2008 2:19 am

Unlikely you'd see a compression test showing low for HGF unless it was literally pishing out the header tank when you cranked it over . . . also remember cylinder pressure is very low when you don't have a huge fuel/air explosion inside it . . . which is what drives gas past the fire ring

Steve - when you rev the engine the coolant drops . . . this is the important observation - you still have air in the system . . . else where could the incompressible coolant go ? . . . the increased water pressure when you rev the engine is compressing the air whereveer it's stuck (the rad of course) and hence the coolant level in the header tank drops . . .

The old overheating at slow speed is always air in the rad in an elise . . . no matter how many times people convince themselves it's something else . . . 99% of the time it's air in the rad . . .

Any outgoing leak in the system (matrix for example) can cause air ingress as the system pressure goes slightly below atmospheric when it's cold . . . hence drawing in air (possibly) every time the engine cools . . .

Constantly dirty /greasy windscreen is probably the matrix . . . I've been through 2 and need another . . . in 90K miles . . . they get salt in them and corrode . . . cr@p design . . .

Fd

Rich H · Post by **Rich H** » Mon Jan 21, 2008 9:19 am

Frosts car restoration guys sell the block tester.

mac · Post by **mac** » Mon Jan 21, 2008 9:56 am

Steve,

If you talking about tonight - then no problem. If your talking about Tuesday night then that's a no go as I'm night shift.

I'll see if I can find my dad's presure testing gear, no promises though as it will be dark and wet by the time I get out of work.

Mac