Saxo - temperature light on coolant ok issue

[alviseven]

Bought a 1998 Saxo for my son last winter to learn to drive in this coming winter with work needed to get it running after a head gasket failure - it was very cheap but 89K and long MOT.
Young son has been super busy under instruction and we have completed the following
stripped head - had it skimmed - new head gasket and replace set tappets etc
Serviced oil/filter and cambelt/tensioner
replaced thermostat, radiator and cap and water pump.

Car starts and drives and had ticking over for several hours with the heater on 3 full blast it is fine - external laser temp gun says 65 deg at top of rad and 55 deg at bottom hose but the head gets to mid 90deg sometimes a little more but the moment I turn the heater down to 2 the temp light comes on too. max temperature I can find on the head apart from the exhaust ports is about 105deg at times but even the temp sender boss is never seemingly above about 75 when the light is on!

Have therefore replaced the temp sender unit too but no avail. it will run on the road for about 6.5miles before the same temp light comes on but the heater still needs to be on constantly.
I have flushed the system from the top hose through the block and heater to the water pump and water flows, I have repeated this through the top hose through the radiator and up to the water pump and water flows just as freely - I have run the engine with no thermostat and this makes not real difference just longer for the light to come on and slower to warm up as you would expect.

The system does not loose any water at all so am confident the head gasket is now fine, compressions are good all round and tappets are adjusted and quiet. Have tried thinking about everything I can - not new to this game but this one is about to stump me.

Anyone shed any clues - beginning to think the heater circuit is the only one to be a full circuit and the head is somehow blocked but there was no sign of this when the head was off and nothing was dropped inside beforehand etc.
Is it an electrical issue and not a coolant issue any more?

Before HGF the car was running with the previous owner fine and before the head was done I have had the rad fan cut into operation on the rad when the engine was hot but since the head been skimmed and done I cannot get the rad hot enough to get the rad to operate at all.

It is now a massive puzzle to me - any ideas please

[Stickyfinger]

Are there not 2-3 temp senders on that age car ??, you say "changed the....", that implies you only changed one.

On the block right side (B/Y) , nr thermostat (G/Y) housing and normally one on the radiator (unsure of colours) but not always/depends on year/engine/ECU I think.

Bleeding the system, did you do this correctly using a header tank "head bottle" and via the bleed valves ?

The fan not kicking on correctly would say faulty sensor to me....worth checking the fuse as well however that could (most likely) be a separate problem.

A faulty sensor will/could effect the emissions/how well the car runs..........

[ozvtr]

There is a cylinder head over temp sensor under the thermostat housing. It has a blue connector.
You can disconnect this plug and leave it off, if it's the failure point. It's called the coolant level sensor but it has nothing to do with the coolant level. After 2005 the TU3 and TU5 engines did away with it altogether.

Failure of the radiator fan circuit will also cause the temp indicator to show full scale even though the engine may not actually be overheating! No matter what, if the temp gauge indicates over temp, the radiator fan MUST be running! If the temp gauge shows over temp and the cooling fan is not running, there is a problem with the radiator fan circuit.

If the temperature gauge shoots up instantly, that typically means that there is a fault of some sort with sensors or accessories, but not an actual cooling fault.
If the temp goes up slowly, that usually indicates a cooling fault.

[alviseven]

I must look at the radiator fan circuit then since I definitely get a temp light and no sign of the fan kicking in. I thought the rad top hose never getting hot enough was this issue but this does not explain the 6.5miles run and still it over heated?
Thanks will check this.

Yes I replaced the green sensor only but think this was actually working fine anyway...
Yes I am certain that I have bled the water circuit properly and its full.

I wondered if there was a blockage at the water pump end of the cylinder head so the water was going through the heater circuit only and not fully circulating in the heat as a result but have no real evidence of this just a hunch.
Thanks

[PaulC5]

If it has air con switch that on since that will start the fan up as a test to see if the fan works.

Since you say the fan worked before you did the head gasket maybe you have damaged some wiring - as far as I know the fan is switched on/off using the temp sensors on the cylinder head/thermostat housing if like our 2003 C3 with the 1.4 petrol engine. I had other cars where there was a temp sensor on the radiator that switched the fan but these were not Citroens. On the C3 the fan would start at 96°C, shown using a code reader with live data.

[alviseven]

that might explain why the car will overheat when ticking over and the heater is not on full blast but it does not explain why we have an issue when we drive constantly and relatively sedately for only 6.5 miles with constant stream of air over the radiator and yet the light still comes on?
Have checked with another car (1990 rover 216) which was up to temperature when it came back from work and the thermostat housing is definitely near 90 deg which on the saxo it never gets to and the top hose to the rad was a lot hotter to touch than the saxo ever gets even when the car is showing a red temp light..
This is a basic car no air con - does a standard code reader work - I have one but had a play yet just been using a laser temp hand held sensor

[PaulC5]

I think it was 2001 when petrol cars had to have standard OBD connections but it is possible earlier ones may have it. You just need to find the OBD socket, on our Citroens it has been next to the dash fuse box.

[ozvtr]

that might explain why the car will overheat when ticking over and the heater is not on full blast but it does not explain why we have an issue when we drive constantly and relatively sedately for only 6.5 miles with constant stream of air over the radiator and yet the light still comes on?

Given the symptoms I would suspect a blocked radiator. Particularly if you need to turn the heater on to keep the temp down when the car is at speed.

[alviseven]

Maybe but the rad is brand new and flushes water through no issue at all - changed the rad as I was concerned with the state of the old one. That is what is so frustrating the car has had new everything really.
New radiator and cap, New water pump, New sender unit, several new thermostats and one cut open on (just takes longer to heat up) and a skimmed head with new head gasket and all the bits to suit etc. What else is there to change!

I do feel that I have a blockage somewhere and the water is not flowing through the head but through the heater system - I plan if I get time this weekend to remove the heater hose and see if I can flush water easily down the top hose input and through the block past the water pump and back to the bottom hose so I can prove that there is no blockage but having had the head off and know it is clean inside by the liners and nothing was left in the system before we put the head on etc I am still not hopeful and at a bit of a stand!

[PaulC5]

I think you should get it plugged in to see what temperature all the sensors are showing before doing any more mechanical work. It could be a sensor /connector/wiring problem. If the sensors you have put on are copy parts they might not work as well as ones from a dealer. Even if you go to a dealer the £120 or so they might charge can be a lot cheaper in parts and time to point you in the right direction.

Both our C3s have shown false high temperatures, the 2003 one did it a couple of times in freezing weather on the M62 a year apart and nothing wrong was found. The 2010 C3 had a common fault caused by the temperature sensor and it was fixed by the dealer following a technical bulletin by fitting a second sensor and wiring loom and the old one disconnected (cheaper for Citroen than a new housing).

[Stickyfinger]

From what is written it all seems to point at false/confused readings from sensors....

Just to confirm....there is no physical sign that the car IS overheating ? (other than the temp gauge ?) such as steam release via the header tank overflow pipe etc ?

[alviseven]

Nope no steam released or water lost the last few times I have had it running. It was ticking over last weekend for getting on for two and half hours but always with the heater on full blast but ran fine other than red light on when the heater was turned down! It is currently off road as big lad is too young to learn at the moment but even so the top hose never gets hot enough to not hand hold easily and the temp in the head on the laser gun only ever reaches about 105 max in places but its hard to monitor from the position of the exhaust valves. The temp sender area boss never seems to get close to 90! Never had anything like it and I have 14 other cars and never paid a garage to do anything so you get the picture - getting splinters with all the head scratching!

[Stickyfinger]

As you are confidant it is not overheating I am not sure why you are worried about blockages etc....why would you not investigate what seems like an obvious sensor problem ?

[ozvtr]

changed the rad as I was concerned with the state of the old one.

Do you have any reason to suspect the old radiator is unserviceable?

Where is the "blockage" going to be?

The heater is tapped off the thermostat housing and then back to the water pump inlet. It is actually aiding in the cooling (according to your statements). So the blockage is not there. And it gives you a hint that the problem is probably not the water pump, the block, the head, the thermostat housing or the heater core. Jury is out on the thermostat, but I'll get to that.
The "bottom" hose goes around the back of the engine to the water pump. A fairly long way, and a possibility of a blockage here. A Piece of vinyl tubing shoved down here should tell you if it's got crap in there.
The water pump inlet and outlet to the block are very visible when you remove the water pump. I assume a build up of crap in those orifices would be very visible? The water pump outlet is also very visible when you remove the cylinder head and peer into the block. Did you see anything there?
The engine runs a wet liner system so it's highly unlikely that the block is full of crap...but possible. I assume you had at least a cursory glance at the state of the block and liners when you had the head off? So lets assume the block is OK.
The liners and block can get coated in crap BUT that only reduces the transfer of heat from the liners to the coolant. Meaning less heat is transferred into the coolant and the coolant runs...cooler (but the cylinder head and pistons run hotter). The same theory goes for a blockage in the cylinder head. This is another reason for the "blue" cylinder head sensor (if it has one).
If the machine shop is worth their salt, they should have chemically cleaned the head, crack/pressure tested it, done a valve job (the exhaust valve seats would have been s**t) and checked the camshaft journals for concentricity! So there shouldn't be any problems with the head.
Next is the thermostat housing. You need to remove that to remove the camshaft to get the head skimmed. No crap there?
You said you replaced the thermostat. Is that working correctly? It's easy enough to test in boiling water. An old pot of water on the stove works fine. It's either open fully when the water boils...or it's not!
Next is the "top" hose from the thermostat housing to the radiator. Short and easy to tell if it's blocked (highly unlikely).
The expansion tank. I don't think a blockage of the two lines to the expansion tank would effect the engine temperature. Only if the system was loosing coolant and the expansion tank could not top up the system.
Last is the radiator.
I'm sorry but I've been working on "stuff" long enough to have learned that just because it's new, doesn't mean it's good!!!
So my suspects would be the radiator or the thermostat (despite them being "new").
Of course there is a possibility of a blockage someplace else, but I've outlined how you might find it.

Temperature sensors. Do both the old and new sensors display the same symptoms? If so, the assumption would be that the sensors are OK and that you have an actual cooling problem.
I do not know at what point the "temperature" light is suposed to come on. But I would assume the engine is running hot enough to turn the light on, but not hot enough for the system to boil over?
I have found that the "green" temperature sensors either work or they fail completely. They don't tend to "sort of work".

Again, does the radiator fan come on when the temp light comes on?

[alviseven]

I have read your reply and can hear your frustration and trust me it is desperation that has driven me to post this and I do thank you for your time and effort to go through the symptoms but you are now at the point where I am ...

I'm sorry but I've been working on "stuff" long enough

all you forum chaps are agreeing with me that the result is obvious if you check the system and have done all the cursory checks whilst the job was ongoing and I agree with you all.

Please I am not trying to sound smug but let me go through this and explain.

The "bottom" hose goes around the back of the engine to the water pump. A fairly long way, and a possibility of a blockage here.

I have had water flowing from a hose from the top hose outlet through the top hose into the radiator (with the new cap on the expansion tank) and then through the bottom hose up to the water pump housing when the water pump was being replaced. I did get a small amount of shale and rusty type filings out in the water but it was like a few tea leaves in a cup rather than a massive blockage (and I have done a hot engine test since anyway) so I am confident that the lower hose and also the new rad is not blocked.

I replaced the rad mainly due to the previous owner who was told it would be their next point of work by his "rather lame and lazy garage" - (in my opinion they did not want the work on such an old car) The outside looked fine and I was not certain that head gasket repair juice had not been attempted at some point despite the fact that the rest of the system did look clean. Plus it was not that expensive and I felt with the new head skim and trying to make a reliable car for my lad it was silly not to. Surely if the water flow through the top hose through the rad and bottom hose this is a good enough check for a blockage here.

The inside of the liners looked great - it is only an 89K mile machine and I was very careful not to disturb them as its the first wet liner car I have worked on - the 90's Rover R8 Honda engines I have are solid block and I think my old daily astra was too - but otherwise my cars are all 1960's or earlier. You are correct to imagine that I did have good check around them and the inlet and outlet points did not appear to be any cause for concern and I did not drop any rag or rubbish into the system when replacing the gasket or head. The old water pump when removed after the HG was done did have quite a rusty looking impeller but this was not again unduly worrying to me and did not leave a chunk of crap in the housing either. Similarly the thermostat housing was clear and has a massive aperture through it anyway.
I have replaced the thermostat twice as the first one was seized and pretty certain it was the cause of the HGF in the first place just the garage never spotted it for the previous owner (it went to them at great cost several times before it was towed dead to them!!) I did this before the HG was replaced in a vain hope that it might not be the head but the water was then cooking and rising and bubbling clearly a HG issue despite not finding any compression issues on the bores.
I have tested both the new thermostats in water several times in between some of the hot engine tests as I would have money on these not opening as the top hose is not getting hot enough and once can still clearly place a hand hard around it when the temp light comes on which should not be the case.
I have also cut one of the new thermostats apart to make a test unit with no innards in so water can clearly flow through it and so is not an impedance and have tried it - engine just warms up more slowly but same symptoms. I have also drilled a 1/8" bleed hole in one of them and put this hole at the top of the rim to aid with the bleeding of the system.
So to all attempts of mine I have tested the thermostat but I am still not 100% convinced that either something else is stopping it open or it is not working but both the new ones pop open instantly in hot water immediately before they get a engine test I am getting that paranoid - had a buy a second unit since I had thrown the original away so had to sacrifice a new one to get a open one!
The head was skimmed by a local shop to me but he only faced the block. I never actually took the camshaft out - I know I should - but its a cheap job not a car to keep. However having taken the valves out I did go through with my lad how to grind in the valves and we did both the exhaust and inlets - the exhausts of course being slightly worse and even at 89K were showing signs of age. replaced the stem seals whilst there too and blew out all the skim swarf with air and then washed the whole head down in degreaser and I was confident that the head was not blocked or dirty etc.

the assumption would be that the sensors are OK and that you have an actual cooling problem.

Quite agree and think that I wasted my money on the new one - its a green head one below the thermostat and there is another blue on next to it but I understand this one is a little pointless and have not touched it - again these were things that were left in place when the head was skimmed and never touched till I replaced the green one post engine test to see if it would solve the issue since I was by then pulling at hairs to solve the issue as I had done everything else!

So having got this far you can see I think I have been pretty exhaustive in getting to the point where I am as frustrated as you guys are with me posting this stuff for help!

Again, does the radiator fan come on when the temp light comes on?

no it doesn't but that is because the rad is not hot enough to trigger the sensor 65 deg tops on the top hose area (unless the sensor is the same as the green red light one? but even this only gets to about 85 tops) It did work before the engine was taken apart so I have seen it work but never since I have reassembled - the wiring all checks out - I have yet to try to see if the motor powers but I am confident it will and I did not yank or stretch the cables so have no reason to suspect that the cables are damaged but appreciate it might be but but the temperature of the unit tells me that the rad fan sensor would be silly to even consider coming on as it is not hot enough to warrant it despite the temp light coming on and the head being around 100 to 105 in places. The thermostat housing still registers not hot enough to open!

I will report back to you all after I have tried yet again the cut open thermostat to take this out of the equation.

I keep coming back in my mind to the idea that somehow the water is not flowing properly through the head. The heater system is almost being used as a bypass and only taking a tiny amount of the hot head water with it to the thermostat housing which is flowing a little due to the bleed hole I have drilled in the unit. Head must to my idea be blocked at the water pump end on the head side and so the water is going around the heater and to the thermostat and then small amount getting through bleed hole (or removed thermostat unit) and thence back round the system to the heater and the rad. I think if I disconnect the top heater hose from the thermostat housing and put a finger over it and them pour water down the top hose - with the thermostat removed - and see if the same amount of water will flow out of the bottom hose when disconnected from the rad I can then in my mind check that the water flow through the head is actually ok. I have checked that the new water pump does make the water move by filling the system as best I could with the top hose off and a hand over the top rad hose point and then getting the engine started to see if water was pushed out of the top hose and it was but it was not exactly fired out but it rose and started to spill on the brief twist of the key. However I have no proof that this is coming through the head and not the heater system if you follow. Plus it is an easy enough check to complete.

Hopefully you can see why this is doing my head in now - it has stumped me to the point where I do not understand! Even have a friend involved who used to rally 106 cars and knows the engine well. Busy the weekend so its off the list of jobs - out in the fiat 500 tomorrow on a run and out today sorting and washing another couple of cars.

Further Saxo work - Got a sunroof seal to buy too. anyone used the one from the ebay supplier? looks like it will do the job. I have just finished the osf inner arch repair just the inner liner to replace back in the car then a small exhaust leak to find and a seat connection to clean to try to clear a airbag fault and it is a fixed car providing I can sort this temp issue. Even considered trying to find a different engine to drop in but am certain the one on this car is actually ok but something silly is wrong.

Many thanks for all the suggestions and I will go back and check as many of these as I can do or have not yet done even if it is a repeat job.