increase in coolant operating temperature after drain, flush, bleed and refill

[jlmacd]

Just did a coolant change for the first time on my 2.0 HDi 110.

Been having some very strange issues for quite a while now with the coolant level sensor light intermittently coming on, then going off again, seemingly dependent on driving speed. No obvious signs of a leak so have made the assumption it may be air in the system.
I have had the car for just over four years and never had the coolant replaced, so decided it should be done and, at the same time, get the air out too.

Did the following:
Drained and refilled with Prestone Flush. Ran for the recommended time then drained and flushed out thoroughly with clean water.
Replaced the old thermostat with new one - both rated at 83C opening.
Refilled the system with a 50/50 mix of Prestone/De-ionised water and bled the air out etc.

What is puzzling me is that before doing this, the car always operated at around 75C (on the coolant temp gauge) rising to about around 90C in stationery traffic etc. Now, however, the temp rises to just below 90C and sits there. This alarmed me at first but there is no overheating going on.

Am curious if the previous (lower) operating temperature I had been used to was actually normal or incorrect - if so, why? Was the old thermostat faulty maybe?

Wondered if anyone can anyone verify, is 90C the correct (normal) operating temperature for the 2.0 HDi 110 ?
I was tempted to put the old thermostat back in thinking perhaps the new one was to blame for the higher temp?

By comparison, I also drive the 2.2l petrol Coupe and had noticed it normally operates with the gauge at just below 90C so maybe the 75C on the HDi has been misleading me for years??

After the coolant and thermostat change, annoyingly the situation with the intermittent coolant level light is still persisting. Despite running the car for nearly an hour to try bleed all the air out (using a 'header tank' bottle on the reservoir) all seemed well. After driving for a day or so, the light was back on.
Strange symptom is that if the car is being driven at speed (on motorway for instance) the light will stay off. once back into urban driving it will come back on. Can't figure this out - perhaps a blockage? As I said, despite the low level warning, it has never overheated thankfully.
Need to investigate further....!

[steve_earwig]

My HDi always sat on the 9 of 90 (the only time it went over was when it was loosing coolant), I suspect the 75 meant your thermostat was stuck partially open and this new one is working how it should.

When you get the low coolant light what is the level like? Is it actually low?

[jlmacd]

Thanks Steve. Yes, after checking when cool the level has dropped a bit - enough to trigger the sensor on the reservoir. (Sensor tests as being good btw)
What I can’t get my head round is why, once it comes on at lower speed, it will then go off again once car is being driven at higher speed 60/70 on trunk road/motorway. Expansion I know but is there air at play here too I wonder?

Guessing there has to be a leak somewhere but can’t locate it. No evidence of white smoke from exhaust or any of the other telltale signs of head gasket failure.
Cam belt and water pump were receipted as done at 55k - (I bought it at 66k) - car now at 103k. Maybe water pump is failing?

[steve_earwig]

Air in the system? Maybe, but if it's only slight it should clear itself. How much coolant are you adding? If the radiator gets hot (i.e. from a cold start) when the engine's idling then the pump should be ok.

[jlmacd]

Probably just under half a litre.
Have noticed there’s also an ominous ‘whirring’ sound present now when running - in the area around the alternator. You can hear it on startup and it continues when idling.
I will check the rad as you suggest. Heater seems to be all functioning - right up to 30c.

[steve_earwig]

Half a litre?! That sounds rather a lot

in the area around the alternator

Oh crap, that'll be the water pump

[frog]

I've seen this two times; once in my vehicle and once in my brother's. My experience seems similar to wat TS reports: no problem driving on highway, but in urban driving the dashboard light would sometimes come on. Especially when driving uphill, strange enough.

In both cases, replacing the sensor in the expansion tank cured the problem.

I think filling up the expansion tank too much will only cause it to overflow as the coolant gets hot. In my vehicle, the coolant level inside the expansion tank is at a steady but low level.

[batrst]

the sensor in the header tank are sh*t . if you take them out and clean the ends of them some time that works but ive change 2 on 406 just puts light on for no reason . and 50/50 mix is fine .you need to make sure you have air out of the system. theres a bleed nipple on the matrix . and one on the water houseing at front of the engine .

[cwhaley]

Did you manage to sort this? I had the coolant light coming on and off for around two months. If I'm honest I ignored it for a while, because after checking the rubbish expansion tank I could see fluid in the 'channel' which is visible with the cap removed. However, one day last month I noticed a large pool under the car and confirmed it was coolant, further confirmed by a dry-looking expansion tank! Turned out to be a broken metal coolant pipe. Garage replaced it and it fixed it for a while.

Now the light is coming back on and off. Haven't seen any leaking coolant (yet, will check on my car at dinner...) however when I checked below the cap the channel was dry. Topped up with the emergency 50:50 mix of coolant I carry, however I imagine this is introducing lots of air.

Before I query it with the garage, I'll try and bleed the air out. Think I remember little thumb screw bleed valves. Best opening these when the engine is hot?

[jlmacd]

Transpired to be back pressure, most likely from beginnings of head gasket leakage, forcing coolant out the reservoir cap.
Finally arrested the problem by using Steel Seal.(Most people are negative about this product but it definitely worked for me) Been about two months now so, fingers crossed, long may it last!

[PeterN]

I had a similar problem with an XM some years ago, it persisted for many miles until one day 'up north' all the lights came on including 'stop' and it had indeed blown most of the water out of the overflow, I refilled it and drove it with the filler cap loose, temperature went back to normal and I drove it like that for many more miles.

If the HG leak is only slight it will behave if there is no pressure in the system but bear in mind it decreases the water boiling point so don't hammer it.

Peter

[jlmacd]

Thanks Peter.
What is it that lowers the boiling point - the addition of the steel seal? Why is that then - just curious!

[frog]

Thanks Peter.
What is it that lowers the boiling point - the addition of the steel seal? Why is that then - just curious!

It's just the pressure that increases the boiling point. As long as the coolant system is closed, it can build up pressure. Water under pressure boils at a higher temperature than 100 deg C. I've easily seen 110 degrees on a long, 130 km/h hill climb, fully loaded with a roof box on top.

If the coolant system cannot build up pressure, you don't want it to go beyond 100 degrees, or the water will boil and the cooling effect will be gone.

[jlmacd]

Interesting. Thank you for the explanation.

Thought all was well - no overspill from reservoir cap happening now and no reoccurrence, thank goodness, of the ‘low coolant level’ warning light coming on.
However, after a drive at speed yesterday after I parked up for about ten mins and then restarted the engine the car overheated! First time this has EVER happened - car has always stayed at the 88C mark - occasional slide up to 90/91 maybe but has never overheated with the STOP warning and beeping going off. I drove on a bit and, oddly, it rapidly returned to 88C. It slowly crept back up again and reached overheat by the time I got home, about 15mins later. Very odd. Then again, the outside temperatures are extreme at the moment!
When it cooled I got the cap of the reservoir and it was looking dry - strange the coolant level light hadn’t come on though?? I topped it back up with more Prestone (50/50 mix) til it appeared in the bottom channel of the filler neck.

Strange thing being, the day before I took the car on a 120mile round trip via the M25 and back and, when I got home checked under the bonnet. To my delight there was no sign of overspillage out of the coolant reservoir cap, as there had been for a few days after the installation of the Steel Seal (possibly from slightly overfilling I reckon).
I had wiped all the spillage residue from the reservoir tank top before departing for the 120mi trip - intentionally so I could check for any spill on return. As there was none, I figured ‘great, the system has finally settled down !’ Apparently not though after yesterdays events.
So, somehow it is still losing coolant somewhere. Could be the first bottle of Steel Seal hasn’t quite completely sealed. the head gasket leak? Am going to put a second bottle in to see if that finally cures it. Fingers crossed once again !

[frog]

Could it be just the coolant temperature sensor that is giving wrong values?

Starting the engine then immediately seeing an "overheating" warning sounds that in fact there is no overheating at all. So maybe just a sensor issue.

On my HDI the coolant level in the overflow tank is always pretty low. There needs to be some space in the tank so that the coolant can flow into when the pressure builds up e.g. at hill climb. If you fill up too much, the excess will only be pushed out during the next power-intensive ride, so after cooling down the level be back to the (default) low level.