Bizarre Problem - Any ideas?

Rodge

Bit of a long story here but this car has my heart broken.

00 Ford Focus.

A couple of weeks ago I noticed the car was overheating a little when I was on the motorway for ~20 miles at a solid 75 mph. When I lift off it went back down to the middle very quickly.

Its definitely not water pump/radiator/thermstat.

The mechanic says that he has heard that a washer under the Cylinder Head Sensor might do it. So he puts a washer on it and now it takes longer for the car to overheat but it still heats eventually.

Seeing as that didnt work he thinks either a new Cylinder Head Sensor wont do it and that the head gasket is gone or going. I dont think this is the case as surely my car would be undriveable if the head was gone.

This only happens when driving at speed and never when parked or in traffic.

Has anyone ever experienced anything similar or have any ideas?

The_Magoo

Car would be drivable sometimes in the early stages of head gasket failure, however if the gasket was gone, it would overheat in traffic and not at road speeds as the air flow would keep every thing cool. Try the new sensor, modern car electrics are very tempermental!

BrianD3

It wouldn't be unusual for a cooling system problem to only manifest itself at high speed. On the M-way at 75 mph your engine will be doing around 3.5-4k rpm. An engine revving at this speed produces an awful lot of heat, much more so than a car sitting in traffic. The airflow is obviously high at 75 mph but if for some reason the coolant is not circulating as it should then the engine will not be able to take advantage of the airflow.

You sure it's not a water pump, thermostat or rad problem? Faulty cap on the expansion tank is another possibility.

Are there any coolant leaks or signs of HG failure. What sort of condition is the coolant in (is it rusty and old etc.) when was it last changed.

It is entirely possible that it could be a faulty sensor. Dunno about this washer business though. Apart from the temp gauge reading are there any other signs of overheating. If you can borrow a digital thermometer with immersion probe from someone you might be able to check the coolant temperature in the tank and see if it's as hot as teh gauge is saying.

Rodge

You sure it's not a water pump, thermostat or rad problem? Faulty cap on the expansion tank is another possibility.

They have all been taken off and new ones tried so it shouldnt be them. I had it for two days over a weekend with a fully open thermostat (a cut in half one) as the mechanic couldnt get a new one till the Monday. With this it drove fine and never got near halfway except when in traffic but it never went above half. I meant to say that in the original post but forgot. IMO if it was the head gasket doing this wouldnt have kept it cool?

There are no signs of coolant leak and the overflow tank isnt losing coolant. The coolant is brand new since last week.

I'll try and get a thermometer and test the temp when it goes over the halfway line.

Could it be a fuse or relay linked to the fan? I hear the fan when I am at idle but isnt that the low speed one and it kicks in differently at speed? I dont know really, just guessing.

Thanks for your thoughts and help

BrianD3

Hmm, it sounds like most of the obvious things have been checked/replaced. I'm assuming that the thermostat in it now is a new unmodified one. I'm just wondering if it could be something like a dodgy rad hose. The hose might look fine from the outside but the inside might be restricting the coolant flow which would limit flow through the rad.

A heater matrix restricted by scale deposits could be another one although I think unlilkely in a 00 car. Does you heater work ok? In general does the car run ok?

A very remote possibility is a brake binding slightly casuing the car to have to work too hard at speed for the airflow available. You would surely notice other symptoms (eg burning smell and worn out brakes) if you had binding brakes though.

Rodge

Everything else works ok, heater has plenty of heat and I have had no problems with the brakes but I will have a look at them just in case. The thermostat is a new unmodified one. The car runs pretty well too, there is the odd shudder at very low revs in second gear but nothing really noticable.

I might have thought a rad hose too but when I had the thermo fully open water was circulating perfectly which put me off that theory.

Its a real mystery to me whats wrong with it.

BrianD3

Tis a bit baffling alright. I'd imagine if it were the temp gauge sensor that was faulty you would get puzzling temp readings at random intervals or all the time but not just when driving on a motorway.

I will have another think about this and get back later, others here should be able to make suggestions too.

For now if you find the car is running too hot turn the heater on full blast and open a window, you will get some extra cooling which will keep the temp down a bit.

Rodge

I'd imagine if it were the temp gauge sensor that was faulty you would get puzzling temp readings at random intervals or all the time but not just when driving on a motorway.

When I read this I did think to myself, does it only happen on the motorway or is there some randomness to it and I do actually think it is a bit random.

For example, last night (I live in Portarlington) I drove to Kildare via the motorway to collect the missus from the train. On the way there the temp didnt move a milimetre and on the way back on the motorway it didnt move either but on the way into Monasterevin at 60 mph it went up to a 2 o clock position. And then after that for the last few miles home it went up and down a few times.

I'm getting a new sensor put in tomorrow or Thursday so we'll see how that goes.

BrianD3

Judging by this behaviour I'd almost bet that it's something to do with the gauge. Hopefully a sensor swap will cure it and it's not something that requires more investigation like a voltage issue.

I have encountered dodgy gauges before, one instance was where the gauge would suddenly read ~30 degrees hotter than it should have at random intervals. First time it happened I nearly had a heart attack. But after investigating it I found it was a spurious reading.

AMurphy

Rodge wrote:

When I read this I did think to myself, does it only happen on the motorway or is there some randomness to it and I do actually think it is a bit random.

......

I'm getting a new sensor put in tomorrow or Thursday so we'll see how that goes.

I'd start with a sensor, and replace that Thermostat you cut with an OEM part of correct specification.

Also, check whatever belt runs the Water pump is not slipping, poor circulation is a possibility.
Another, cooling hampering condition is debris in the radiator, both inside and outside. Leaves, papers, etc often collect on the front and block the air. So check and clean the outside. You could run water backwards to airflow, from a low pressure sprayer, not a Hi-pressure washer, as the pressure can bend the fins.
And, if your garage man has a IR spot type thermometer, you could check for cold/cool spots on the radiator, these spots indicate blocked internal channels.
Or, if done carefully, you could use you hade to look for the cold spots.

Also, check how this condition responds to the internal cabin heater being run.
If it responds well, if no cabin heat and the gauge goes up. Maximum heat and the gauge goes down. Then I'd go for the clogged rad.
If it does not respond... I'd suspect teh gauges and sensors.

Rodge

BrianD3 wrote:

Judging by this behaviour I'd almost bet that it's something to do with the gauge. Hopefully a sensor swap will cure it and it's not something that requires more investigation like a voltage issue.

I'm hoping too.
It went up a little bit yesterday so I stopped the car immediately and checked the water, there was a good bit of pressure. I opened the cap, it didnt boil over but the water did come up a bit. I checked all the hoses and they were all fine bar the thin one from the back of the engine to the overflow tank. This was red hot. Is this normal?

I'd start with a sensor, and replace that Thermostat you cut with an OEM part of correct specification.

Also, check whatever belt runs the Water pump is not slipping, poor circulation is a possibility.

The thermostat has been replaced and a new radiator was tried on it too to no avail. The outside is clean and junk free.

When it went up yesterday I also turned off the heating, turned it on and changed it from hot to cold and vice versa and it made absolutely no difference at all.

Nom-IzZ

Rodge,

A few questions for u? does your car over heat when your heater seating is fully turned onto cold?

Try put the heating onto fully hot and this should solve the problem.

Ford badly engineenered the HCV or heater control valve located in the bulk head in the fiestas and pumas, i presume the same part was used in the early focus models.

Simon

Rodge

I've tried putting the heat onto full and it hasnt made a difference at all.

mark 666

it could be you head gasket take youroil cap off if there is creamy gunk in there its your head gasket do you drive the bollox out of it

Rodge

there's no gunk in it and I have never driven the bollox out of it. I only have it 4 months and my father (who has never been over 60mph in his life) had it before me.

I always thought that if it was the gasket it would heat no matter what. My yoke does all sorts of strange things. It has never overheated in traffic. Only when going up a hill or on the motorway or something like that.

Who knows though, knowing my luck it'll turn out to be the head gasket and cost me a solid fortune.

BrianD3

Based on what you've posted I think blown head gasket is unlikely. Even if there was mayonaisse under the oil filler cap that would mean very little unless there were other symptoms of HG failure.

I still think it's the gauge/sensor.

One thing to remember about the gauge is it could be very insensitive (when working properly) This is the case on the Mk2 Focus that we have and the Mk1 is probably similar. The gauge is deliberately designed to be insensitive and barely move once the temp is within the normal operating range which can be quite wide. If the temp goes outside that range then the needle may move dramatically. This is so that the driver does not get alarmed by the needle fluctuating at normal temp and the gauge only "does something" when there is actually cause for worry.

Rodge

You were right Brian, the sensor change did it.

The new sensor looks a lot like this



but the old one was shorter and stubbed at the end like it had been squashed. Never seen it before myself but I drove to Swords and back this morning without the needle moving a millimetre.

Thanks for all your help lads.

The_Magoo

The_Magoo wrote:

Car would be drivable sometimes in the early stages of head gasket failure, however if the gasket was gone, it would overheat in traffic and not at road speeds as the air flow would keep every thing cool. Try the new sensor, modern car electrics are very tempermental!

told ya so! Good news, glad we could help!

BrianD3

Just thinking about this some more - if the car really was overheating, wouldn't the fan have been on all the time (assuming the fan was working of course) The sensor for the temp gauge is generally separate from the fan switch. So the fact that the fan wasn't on but the gauge was showing overheating would point to either a broken fan, faulty fan switch or a faulty gauge.

I hope this incident didn't cost you too much in parts and labour to replace unncessary parts when all that was wrong was a little sensor

AMurphy

BrianD3 wrote:

.... The sensor for the temp gauge is generally separate from the fan switch. So the fact that the fan wasn't on but the gauge was showing overheating would point to either a broken fan, faulty fan switch or a faulty gauge.

......

Generally but not always.
My Toy has a sensor each for the gauge, EFI, Fans and A/C, they are all over the damn engine.

My van has one on the thermostat housing. It is used to influence the EFI, A/C, Fans, gauge and A/T.

Rodge

A little explanation of the sensor in the Focus

Cylinder Head Temperature Sensor
The cylinder head temperature (CHT) sensor (Figure 29) is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.

The PCM controls more than just the gauge doesnt it?

Luckily I found a very sound mechanic who after changing the water pump for €110, didnt charge me anything in labour for the new thermostat and new sensor so it was a relatively inexpensive endeavour.