Technical Seicento coolant blowout

[Steve70]

My trusty everyday driver 1108cc Seicento has been suffering from a mysterious and occasional slight coolant loss in recent months. Additionally the heater has been poor, offering only luke-warm air after a long run. I checked the two bleed valves under the bonnet and they both dribble water when opened. Often immediately after switching the engine off after a run, various odd glugs and bubblings can be heard from the engine compartment.

This morning (which was very cold!) I noticed there was no heat at all coming out of the vents, so had a chilly 30 mile commute to work. Just as I arrived at work the temperature warning light came on. Opening the bonnet revealed steam and after leaving it for ten minutes to cool slightly, careful loosening of the header tank cap caused the coolant to start to spray out enthusiastically. Obviously my first thought was 'head gasket!' yet there was no mayonnaise in the oiler filler cap, the engine idled as smoothly as usual and no white smoke was to be seen from the exhaust.

I managed to get home with the water topped up and the header tank cap just on a couple of loose turns so the system didn't pressurize. Apart from frequent stops to check the coolant level (which initially increased, before starting to go down) the car drove as well as ever. I did notice though that that the left side of the engine (i.e. drive belt end) was fairly thoroughly wet below under the header tank, as though water had been spraying around, although the tank itself hadn't been overflowing and watching the engine at idle didn't highlight any obvious source of the water.

From the above does it seem likely that the problem is with the head gasket or elsewhere? I'm wondering why the heater went stone cold and the coolant boiled. It does sound like a major air lock of some kind. I probably won't be able to check the car in daylight until the weekend, but thought I'd collect a few opinions from fellow Cento owners in the meantime...

Sorry for the long post!

Steve

 

[glenn2602]

does it seem likely that the problem is with the head gasket or elsewhere?

The cooling system can remain pressurised for quite a few minutes after the engine has been switched off. The coolant level does increase slightly when the engine warms up - that's simply due to the expansion of the water warming up, and then drops when the thermostat opens to allow full coolant circulation.

Check your engine oil dipstick for 'mayonnaise' - the creamy sludge that forms when water mixes with engine oil. Though be aware, not all head gasket problems cause mayonnaise.

Before you jump to any conclusions, get a decent workshop to test the coolant for exhaust gas contaminants. You can buy a kit for this on Ebay, but .. probably a better idea just to first pay a workshop for a diagnosis.

On the other hand you may have a faulty thermostat or a slight weep from the water pump, or even something as simple as a collapsed hose.

I can't see any connection between overheating and no warm heater air. Usually, if a thermostat fails in the open position it allows the water at the front of the engine to circulate, whereas the coolant at the back of the engine overheats/boils... and supplies plenty of heat from the heater!

On the other side of the coin, a jammed open thermostat makes the engine run cool and as the temperature sensor is near/around the thermostat it would be sending an incorrect - cool- signal to the dashboard even though other parts of the engine are hotter than they ought to be.

Don't jump to conclusions and don't start replacing parts in the hope of curing the problem. It's worth paying a decent workshop for a diagnosis.

If push comes to shove and it's a head gasket fault (I have my doubts) try a modern sealant fix which can be bought on Ebay. You add the contents to the radiator, not the expansion bottle.

Let us know how you get on

 

[Steve70]

Thanks for your thoughts, Glenn. Excellent advice and some good suggestions to consider too. I'll get the car booked in with my usual local chap as soon as I can. I trust him and he's usually spot-on with his diagnosis. Meanwhile I'll take a look at the dipstick tomorrow for any signs of mayo. I really must get the car fitted with a temp gauge (as per the guide on here). I've been meaning to and this is just the kick I need!

I will report back with any further findings in due course.

Steve

 

[rallycinq]

The connection between overheating and a cold heater is.......no water.

You need to pressurise the system to find the leak.

It is leaking, it may now have blown the head gasket.

That blow maybe between the combustion chamber and a water way. This type of break will not show up as mayonaisse, just increased pressure in the cooling system.

Whip the plugs out. If one is incredibly clean, as though it has been steam cleaned, there is your issue.

D

 

[David C]

The connection between overheating and a cold heater is.......no water.

Or no coolant flow, ie pump not pumping.

 

[Ralf S.]

The clue is in the original post.. a lot of coolant at the cam-belt end.

My tuppence worth is that the water pump seal has packed up and you're losing coolant through the pump shaft.

Water leaking out, means air is getting in. The air will accumulate in the radiator and the heater.. since they are the tallest points of the system... so they will both feel cool, even when the motore feels hot. The temp' sensor is on the engine.

Jobs for the weekend:

1) Top-up the reservoir to MAX. Use regular tap water for now, rather than waste coolant.

2) Open the bleed screw on the radiator until water comes out. Don't remove it completely or it'll be tricky to get back in while water is gushing out...

3) Run the engine to get water into the heater (warm air comes out). Turn off.

4) Re-top up the reservoir. Dry absolutely every sign of water that you can see, including from the bottom plastic tray, the metal pipe in front of the engine and you name it.

5) Go for a local drive. Long enough to get the temperature up to 86C. Check that the heater works and that the beast runs at usual temperature (Seicento gauge can go anywhere between 82 and 92 usually) and if in traffic that the fan cuts in, cools it down and goes off as normal.

6) Have a cuppa while the beast cools down. Check the reservoir level (guaranteed it will need topping up). Bleed the rad' (guaranteed it will have air in it).

7) Do you have a load of water down the side of the motore, on the cam-belt end? Yes = water pump. No = head gasket.

8) Don't drive the car any more (not even with a gallon of water in the car/topping it up) since the pump can collapse altogether and leave you marooned. Seicento won't however wreck it's valve-gear if the pump (cam-belt is attached to it) fails.



Ralf S.

 

[Steve70]

Thanks Ralf, that's interesting. I'll run through that tomorrow hopefully and report back...

Steve

 

[Steve70]

Ok, after topping up the coolant to max and bleeding the rad (and the heater, whilst I was at it) I took two runs in the car this morning totalling around 8 miles, including hills and some prolonged stationary idling.

There was no external water on the engine. The coolant level remained steady after these runs. There were no signs at all of any distress or overheating. The car runs and drives absolutely as normal, with the exception of the heater which is seems to vary between producing cold air or at best only a very slight amount of warmth. The pipes to and from the heater are hot and it bleeds hot water so what's happening there is strange. (As a minor point of interest, whilst the face level vents have in the past produced reasonable heat, I have only ever get stone cold air from the outlets by the footwells)

Switching the car off after it's run this morning I got the usual few 'glugs' from the header tank for a few seconds. It seems to be a small belch of water coming from the small diameter return pipe that branches off the heater feed and comes in to the top of the header tank. Possibly a clue, possibly not!

Steve

 

[Steve70]

Just done another trip of around 7 miles without drama. The heater is still blowing cold despite the pipes to and from it being hot (or at least warm) to the touch. I'm really not sure how that can be possible as the heater matrix must surely be hot if the pipes in and out are.

Back home and with the engine still running I had another look under the bonnet. The electric fan hadn't cut in (unless that's not working) and there were no obvious signs of overheating, although I noticed on switching off the engine that the radiator cap was hissing for a few minutes. Without a temperature gauge it's very difficult to know what the engine is doing.

Steve

 

[glenn2602]

If there are no leaks the only reason I can think why the heater should be cold is that the matrix is blocked. And I can't think of any reason why the radiator cap should be hissing unless it's defective or under undue pressure.

Be aware that a worn impeller on the water pump can cause problems. I once owned a Merc 2.8 that would overheat and lose water. After changing the thermostat, flushing the system and flushing the radiator, things were no different. In desperation I eventually removed the water pump and sure enough, the impeller blades were worn and unable to shove water around the system.

A slight leak will very quickly dry off on a warm engine. The engine won't reach its correct operating temperature until it has covered 10 miles. Maybe it would be best to drive 10 miles and then let the engine tickover for a while? Something caused your car to overheat in the first place - and faults usually don't go away if they're ignored. You need to find the cause.

I would agree that an electric temp gauge would be a good idea.

 

[Ralf S.]

That's a strange one...

I agree there's something up with the heater... but if the pipes in and out are hot, it's difficult to understand how the matrix inside the car can't also be hot, and produce warm air.

Just an idea... did anyone ever use Radweld (etc.) on the car? That can collect in the matrix and block it.

It might be time to get on your hands and knees, into the foot-well and see if you can feel the matrix to see if it's actually hot or not. If it is, the "hot air" problem might be that the various air flaps are not opening and closing when you slide the direction control bar. If the flaps are not actually opening then you're effectively running with the heater "off" even though the matrix has got hot water in it.

The "overheating" issue .. could still be happening, even though the beast hasn't boiled over for a few days. I didn't realize you had no temperature gauge.

When you remove the coolant cap with the engine slightly warm (don't try this on an even vaguely hot engine) do you get an escape of pressure? Or does it feel the same as just removing the cap when the engine is stone cold?

You should get some pressure escaping (plus potentially boiling coolant, so always keep your face turned away, wear glasses/gloves... or better still, get the lad from next door to do it while you stand 10 yards away.. ).

If you have no pressure, try changing the cap. They're not too dear. Use the same rating as yours (1.2 or 1.4 bar etc.).. Don't fit a higher or lower pressure cap.

Also, get under the car and check for any drips or wet spots under the radiator, on the radiator bottom hose or on the metal pipe next to the engine block.., ideally in the morning, when any coolant has had a chance to leak out without drying off on a hot surface.

If there's no coolant evident anywhere, then we're back at the pump. I changed mine once to sort out a slight leak/running hot problem (in my case I could cool the car by turning the heater on.. ) but even though the pump was slightly leaking through its spindle, it turned out to be a radiator leak that was the main culprit.

You still need to take the beast for a longer drive, or use it for a few days and then try bleeding the radiator (cold) again. A head gasket problem puts a lot of gas into the radiator very quickly, so that sounds unlikely now.. but it might be useful to know if you're still getting air in the system during normal use..


Ralf S.

 

[rallycinq]

Cock trouble, its a Sei not a Cinq.

D

 

[Steve70]

Thanks for the replies, chaps. Yes a longer drive might prove more revealing. I'm almost tempted to try it again on the commute to work but that's 30 miles and it will be no fun at all if it boils again. The radiator cap is holding pressure as it does create quite a release of air when I loosen it cold. Odd that it hisses though when the car is hot after a run. I've not noticed it doing that before and it would suggest perhaps that it's releasing excess pressure.

I didn't know you could touch the heater matrix from inside the car, so I will try and check that out. The heat output has always been a bit poor, although it was only on the day of 'the big boil-up' that began this thread that it ran stone cold for the first time. It has produced a tiny amount of warmth since then on my recent test runs, but would then go cold, then slightly warm again.

I'm not sure whether the heater problem is a clue as to the main trouble or if it's merely a side issue.

Is the heater cock a trouble spot on the Seicento? Is it even accessible?!

Steve

 

[David C]

The Sei heater has a valve on the end to regulate coolant flow through it (the "cock" mentioned above).
The Cinq has permanent coolant flow through the heater and regulates heater temp with air flaps.
Access is via the trim panel at the back of the engine bay.

A stuck cock on the heater will stop the heater working properly, but won't cause the engine to overheat.

A failed coolant pump will cause engine to overheat and heater to be cold (as I mentioned above).

As your two symptoms are cold heater and hot engine, I'd be checking for poor coolant flow.

 

[rallycinq]

I'd also suggest checking your cock.

D

 

[Ralf S.]

I'd also suggest checking your cock.

D

Someone had to go there....


Ralf S.

 

[cc1]

Does the radiator fan work?

 

[blu73]

not been in cento section in a while... any updates on this one??

You said you can hear the cap hissing when you stop with hot engine - it shouldnt do that... Although i agree with the above sentiments this could be due to water flow issues if the cap is hissing and you can't find a leak I'd suspect thats where the water is going, or at least some of it anyway. Change the cap, they are only a few quid. Take the timing belt cover off and look around the waterpump for leaks if the water still goes down after that.

heater wise, again as above there is possible cock trouble, but just to be sure when you have topped up and bled the system you have had the heater set to full hot haven't you?? I think if it were me I'd try a simple back-flush of the heater matrix, that itself should give you an idea of how blocked/dirty it is, and if its not blocked it should make it more efficient anyway so no reason not to. So take both pipes off it and run a hose pipe through it in the other direction to normal flow until you get nice clean water coming out.

Check the fan starts cycling when the cars upto temp - if this is a spi sei this will also confirm the fan switch is working too, mpi is switched by ecu unlike the spi.

the milky residue from hg failure is usually more obvious in the actual oil cap than on the dipstick unless its so bad all the oil is milky which i doubt. tbh a compression test is never a bad thing to try, compression testers are only about 15 quid.