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K Series cooling issues

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Hi all. I haven't posted on here for quite a while but have always received good advice when I have. As always - apologies if covered fully by another thread …

My series 1 Elise is 20 years old now and survived just over 100k miles on its first engine before HGF ended its days and it was replaced with a reconditioned engine in 2014. After repairing I also got myself a little run around car to reduce the mileage on the Elise so have only done ~8k miles on the new engine, however the Elise is now my daily run around again.

A couple of years ago I noticed the temperature reading on the dash was low, down at mid 60s instead of the steady mid 80degC I've always had. I also started needing to top up with coolant on occasion. I had investigation work by numerous mechanics with sniffing for exhaust gases in coolant and pressure testing the coolant lines etc. with no obvious leak identified (there was no mayonnaise in the expansion tank but there are a few dark deposits!). There seemed to be no impact on performance and I continued to drive it, keeping a close eye on coolant levels and temperatures. Also the cooling system remained pressurised even when cold and not driven for days

At my service this year I was told they had now seen the first signs of coolant leakage through the head gasket. I had the head gasket replaced a couple of weeks ago and the mechanic said he could see no obvious fault with the gasket (other than that it was an unbranded part) and that from everything he could see the head was in good condition. There were clear signs that cylinder 2 had been washed clean with coolant flow as it was shiny compared to the carbonised other cylinders.

After a few days of very variable temperatures I enjoyed a couple of days of perfect temperatures for the first time in years, and the coolant system even seemed to depressurise when cold - happy days - but not for long and I'm now back in the  mid 60s again and an expansion tank always at high pressure. I've not had to top up with coolant yet but fully expect to need to soon.

So to the point: what is going on? I'm not a mechanic (probably obvious). Is there anywhere else coolant can commonly leak other than the head gasket (if I assume both replaced and new gaskets are actually fine) to get into the engine? Any ideas why after working on the head all seemed fine but has now reverted? I'm completely at a loss and getting fed up with throwing money at the thing. Are the low temperatures and coolant leak linked or not? Any advice or ideas welcome (and apologies for the long story ….)

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Posted (edited)

I’ve got a S2 K Series with 98k on the clock and I had similar issues of running cold. I assumed thermostat was stuck open and ended up taking it to Gav at Unit 4. 

Gav kindly replaced the thermostat, and examined the thermostat after removal, no sign of it being stuck. However he did suggest that the spring keeping it closed wasn’t holding much pressure and the water pump could just push it open. 

Swapped for an 88 degree thermostat and temp has been rock solid since.

 

Hopefully not related to HGF....this car is costing me enough at the moment as the exhaust has just fallen off!!

 

 

 

Edited by Caligarinet

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Thats extremely helpful - I'll ask the mechanic if he touched the old thermostat at all during the last work. I've been thinking about fitting the remote thermostat kit from Eliseparts as well next time it has some work doing on it.

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Head gaskets can fail in different ways.  Between the oil and water ways, you get mayo either in the header tank or on the dipstick and under the oil filler cap (just the places you can see).  Mayo in the header is a guaranteed HGF because there's nowhere else for the oil to come from (unless you have an oil cooler).  Small amounts of mayo in the oil may be simply expected water that hasn't been boiled off, buts lots of it means HGF.  Or the fire ring can fail between water and combustion, which means you get gas in the coolant and very high pressure even when it isn't particularly hot, and some white smoke on startup with a possible misfire as coolant is blown out of the cylinders.  A fire ring break is the one that can be sniffed, or you might spot sooty deposits in the header tank.  If the coolant starts off with no pressure, then is later under pressure when cold, then something is being pumped into the circuit; combustion gases is the first suspect.  If you leave the car for a while, you might get some coolant leaking back the other way that you can spot when you start the engine, but the fire ring might only pass gas when the engine is running.  Sometimes gaskets aren't fitted quite perfectly and get nicked or trapped.  I've had one that failed immediately, luckily it pissed coolant out on the floor so it was easy to spot.  Hopefully it isn't something more difficult like a porous head.

You might want to check the temperature senders themselves.  As they age, the resistance goes up and the temperature reading goes down.  A poor earth can cause low readings that jump up when loads like the headlights or fan come on.   A stuck or passing thermostat means it will take an age to come up to temperature, possibly never getting there if you are moving.  Try leaving it idling, or fast idling, for 10-20 minutes and the temperature should come up even if the thermostat is open.  You can also check if the radiator is warm soon after startup when the temperature is still very low.

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Ok thanks for that - The temperature goes up 2-3 degC when I turn on the lights so maybe there is something in that.

I do have sooty deposits in the coolant tank but they have been there for ages and don't seem to be getting worse.

Excuse my ignorance but where is the fire ring and is it a difficult job to diagnose/fix?

I've been driving since the gasket replacement - have done about 300 miles including time sat in traffic at close to idling speeds but after the first two days of good temperatures they never go above 66-68 degC. 

My two main worries - are the previous coolant leakage and low temperatures linked or independant faults; and regardless why did I have two days of good readings then back down? Also with the temperature appearing to read low does this affect the time the fan comes on - mine almost never comes on but if I do get stuck in traffic I want to know that I'm not going to cook the engine.

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The fire ring is the metal ring on the head gasket that creates a seal around each cylinder.  If that seal fails then combustion gases will be pumped into the coolant when the engine is running, and coolant may leak into the cylinders.  The gases in the coolant can be detected with a sniffer, which is one way to diagnose HGF.  Eventually, soot will start to build up in the coolant and you'll see those black specs or some scum.  They can also just be bits of corrosion or from an old HGF.

Coolant reading low is obviously something to look at.  Could be the thermostat.  It might work for a while, then stick.  That's assuming the temperature really is too low.  You can get a handle on that by seeing how hot the coolant is when the dash says 60C.  There are separate temperature senders for the ECU and the dash.  The dash one (blue) is less reliable because it is earthed to the engine, but if one is just getting old then the other probably is too.  The ECU one controls the radiator fan.  You can test the fan manually by unplugging the brown one (with the engine running), luckily the one you can reach.  So long as the fan works, you could try running until the fan comes on and see what the dash reads.  It is supposed to come on at about 102C.  If the brown sender is unreliable then the fan might not come on until the engine is hotter.  Need to find out if you're really running at 60C or just the dash saying that.  If you've had the fan come on, do you remember what the dash was reading?  It wouldn't come on at an actual 60C unless something very strange was happening.

A 2-3C rise when the lights come on is common, but does indicate that your earth straps probably need cleaning up.  With very good connections on both earth straps you'll see less than 1C change when the lights come on, and about the same with the interior fan on full.

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You appear to have 2 problems here? First off make sure the cooling system has been bled properly. Also change the sensor for the stack. Cant remember if its the Brown or Blue off the top of my head.

If its still reading low there is a good chance the thermostat is knackered.

The retaining pressure is almost certainly a blow across the fire ring. Did you have the head peened and skimmed after the last time?

I would use the new Chinese gasket personally for a number of reasons. If you do make sure its a 'real' one.

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