1999 1.8 overheating problem? - mikej
Hi folks,

Basically, my 1999 1.8i Focus Zetec (60k miles) has started to overheat (at least, according to the gauge) but ONLY when travelling at higher speeds on dual carriageways/motorways and only when you've got your foot down and are putting the engine under a bit of strain (accelerating to keep the speed up on hills for example)

A few points that may be relevent :

When it happens, the temp gauge will go from it's normal 12 o'clock position to almost in the red really quickly.

Once you're in or near the red, the car sometimes feels almost sluggish, like the power isn't right - could this be the Cylinder Head Temp (CHT) sensor telling the ECU to take precautions ?

Strangely - if you ease off, it'll often return to the 12 o'clock position really quickly too - takes less than 30 seconds sometimes !?

Both the coolant and oil levels are fine and there are no obvious leaks around any of the visible hoses or themostat housing.

You can drive around town as much as you like doing anything up to 40mph and it won't happen at all, not even in traffic on a hot day or at traffic lights.

There are seemingly many causes of overheating and so far I've been lead towards the following : faulty CHT sensor, faulty thermostat and the blue Ford coolant which has never been renewed, so could do with being replaced.

The fact that the temperature gauge can go into the red and then (once you ease of) back again so quickly leads me to suspect a faulty CHT sensor. Unfortunately, according to the Haynes manual - to remove the CHT sensor on a 1.8i, you have to remove the alternator and to remove that, you have to remove the auxilliary (cam?) belt so I may need a garage if I go down that route.

The thermostat and coolant I can change myself first though.

Has anyone had similar problems or can anyone offer any advice ?

Could it be the water pump, fan or anything else ?


Edited by Dynamic Dave on 30/07/2009 at 22:03

Ford Focus overheating - Railroad.
Changing the thermostat is always a good place to start. I always recommend that they're changed at regular intervals (every couple of years or so) as a matter of precaution.
Ford Focus overheating - jc2
If it only overheats at high speed,high load it sounds more like a partially blocked radiator;the next time it happens,open all your windows and put the heater on max heat,max fan speed and see if this brings the gauge down.
Ford Focus overheating - DP
I agree with jc2.

This sounds like a classic coolant flow problem - blocked rad, duff heater valve (common on Fiestas and KAs at least), water pump on its way out. I'm not sure about the Focus, but the Fiesta uses a water pump with a plastic impeller which can break up.

Try playing with the heater settings to see if this has any bearing.
Ford Focus overheating - jc2
If you get plenty of heat out of the heater,it won't be heater valve or pump;if the temp.gauge stays in the middle when not working the engine hard,the thermostst appears to be controlling.
Ford Focus overheating - mikej
Thanks for your input guys.

Was able to test the heater under normal driving conditions today and it appeared to be working fine. Not had chance to replicate the overheating problem yet, as I need a clear length of dual carriageway or open road to really put my foot down to get it to overheat.

"If you get plenty of heat out of the heater,it won't be heater valve or pump"

Do you mean it won't be the water pump ?
Ford Focus overheating - jc2
Ford Focus overheating - L'escargot
The fact that it only happens at high engine speeds suggests that it might be caused by a coolant hose collapsing and reducing the flow ~ probably the radiator bottom hose which will be under suction.
Ford Focus overheating - L'escargot
it might be caused by a coolant hose collapsing .......

Unfortunately it may not be apparent from the outside of the hose if the inner layer has become separated. However it's perhaps worth revving the engine with the car stationary (preferably when the coolant is hot ~ you could let the car idle first until the fan reaches the cut-in temperature) and then looking at the hoses.
Ford Focus overheating - L'escargot
A test to determine whether there is a blockage in the radiator would be to let the car idle and see what happens. If the radiator is OK the temperature should cycle up and down as the fan cuts in and out. The high ambient temperature we're experiencing at the moment is ideal for this test.
Ford Focus overheating - DP
If you get plenty of heat out of the heater,it won't
be heater valve or pump;

Not necessarily. There is an issue known to affect Fiestas, Pumas and Transits where the heater control works perfectly, but the valve imposes a restriction on coolant flow when the heater is set to cold. The engine then overheats unless you turn the heater to its hottest setting.

I spent over £200 trying in vain to fix our overheating Fiesta before I discovered this (new rad, water pump, thermostat etc) and in the end it was the heater valve.

The fix on the Fiesta is either a heater valve bypass kit or a replacement valve (with a specific part number). I did the latter and haven't had a problem since, even in the 32°C we've had recently.

Ford Focus overheating - mikej
Thanks again for the help.

I can't find any reference in the Focus Haynes manual to a 'heater valve' - it just says 'hot engine coolant is circulated through the heater matrix' with no mention of a valve controlling the flow.

Would the Focus definitely have one and if so, could you give me a clue where to look, or could it be known as something else ?
Ford Focus overheating - jc2
Close to the bulkhead usually.
Ford Focus overheating - MikeTorque
Did you find the problem eventually or is it still occurring ?
Ford Focus overheating - solved ? - mikej
Just to conclude this thread, the signs were pointing towards a faulty or failing water pump, a faulty cylinder head temperature (CHT) sensor or a blocked/faulty thermostat, radiator or hose.

I thought I'd start with the cheapest/easiest option first, so I drained the coolant (the blue Ford coolant is good for 6 years and the car is nearly 7 years old, so it was overdue a replacement anyway), replaced the thermostat (easy job on the 1.8i - just 3 bolts to undo the thermostat housing) and topped up with the high spec Ford-approved Motorcraft coolant.

For info, the thermostat plus rubber seal was around £12 and the coolant was £15 for 5 litres from my local Ford dealer (cheaper than Halfords !). Needed just less than 3 litres for my 1.8i, so I've got some spare for topping up.

It's a fair drive to the motorway, so I took the car to the nearest dual carriageway and hammered it up and down for 20-30 minutes and couldn't get the needle beyond the (normal) 12 o'clock position.

I'm fairly sure I've fixed the problem then, although I won't be completely satisfied until I've had a good long drive on the motorway just to be sure !

Ford Focus overheating - solved ? - henry k
Thanks for updating us.
Report back after a "hot" run?
Ford Focus overheating - solved ? - mikej
Had a good long trip on the motorway recently and I'm happy to report that I seem to have solved the problem completely with new coolant and a new thermostat. I could not get the gauge to go above the 12 o'clock position, despite my best efforts to get it to do this !

I've noticed that the car appears to heat up a lot quicker now than it used to, at least according to the gauge, so I think that the old thermostat was stuck in a partially open position that lead to overcooling initially when the engine was first started and then wasn't open enough to allow enough coolant flow through the radiator when the car was under load (ie. up hill at high speeds), leading to overheating.

Anyway - with any luck this might prove useful to someone with Focus overheating problems in the future.

Ford Focus overheating - scubadel
I had the same problem after i renewed my antifreeze ,
when the engine got hot i checked the bottom hose to the radiator & it was cold, i thought it might be the thermostat, which i changed but still made no difference, so i took the radiator off & filled it with hot water & radiator flushing fluid and left it soaking overnight ,because when i first drained the engine of water there could have been some material sitting in the bottom of the block which could have been washed into the fine tubes in the radiator, i also checked the new thermostat in a cup of boiling water , when this was done it would not open until it was fully submersed in boiling water, so i concluded when the engine is hot the thermostat is cold on one side & hot on the other & would not open, so i drilled a small 2mm hole in the edge of the thermostat to let some water circulate around the thermostat , since i have done this my car has stopped overheating when on the motorway, i hope this can help you
Ford Focus overheating - DP_Cheese

Ok, This is the closest thread that I have come across that describes the problem with my focus. If I reach 70mph the temp gauge goes from the middle right over to the right. When I shut off and return below 60 it drops back. Now, this car has been back and to to the garage (and he has a good reputation) multiple times and he has finally held his hands up and threw the towel in (even charged nothing for the last amount of work!!) This is what the car has had done (in no particular order)....

1. New Radiator 2. New Thermostat 3. New Thermostat housing (as recommended by Ford) 4. New Temp sensor 5. Been vaccumm filled with fluid 6. Water pump checked 7. New cam belts

Now, 70mph is not bad, before all this work it was happening just above 50mph. Other mechanics are suggesting it is electrical, though the ECU is working perfectly (been hooked up and monitored).

At this point, I have to discount mechanical (can I?). Could a short in the wiring at a certain speed cause an incorrect temp signal to be sent to the ECU.

One mechanic actually suggested removing the wire from the Temp sensor - at this point I am seriously considering it!!!

Any help anyone?



Ford Focus overheating - scubadel

try the catalytic converter, found out mine was partially closed & was backing up the exhaust gases at the head causing the overheating, have now changed the cat & is running as sweet as a nut

Ford Focus overheating - John F

1. New Radiator 2. New Thermostat 3. New Thermostat housing (as recommended by Ford) 4. New Temp sensor 5. Been vaccumm filled with fluid 6. Water pump checked 7. New cam belts

Any help anyone?

How do you 'check a water pump'? [and how do i get rid of this pesky blue line!] You can't just inspect it.

If its vanes are beginning to fall off, when you put the heater on hot with full fan it will blow out loads of hot air which will soon get cooler, because the heat is extracted from the water in the heater matrix faster than it can be replaced. Also, only the top of the rad will be warm despite the temperature gauge drifting towards overheating levels and/or the warning light coming on.

Ford Focus overheating - 600
My lad is just being towed back having had an over heating problem again. some of the issues described above - over over heating loss of water and no heat in the car. Have just had a new water pump changed cam whilst there and changed a leaking hose.

Again the started to overheat but temp does not drop down when slowed yesterday appeared to have air locks in the system. My son tells me that the car was starting to cut out - Wondering if there is another pipe problem or if its the thermostate as suggested in some of the other threads?
1999 1.8 overheating problem? - driven


did you ever sort your problem out?

I have just gone through the same experience as you with my ford focus overheating

only i ignored the temerature gauge to my peril and blew the engine!!

so a recon engine later, a new radiator a water pump check and a hose and thermostat check its still overheating !!!!!

only now I can get up to 70-80mph before the temp gauge goe red wher as before it was at 60-70mph.... if fact im sure the overheating relates more to the revs than the speed of the car so I would say on a motorway if I keep the revs under 37000 its ok, but if I push it over then it overheats again (with or without heater or air con)

some one said the catalitic converter could be partially blocked ?? but how would you check that ? the car revs fine it will hit 50-60000 through the gears no prob

Any help would be greatfully recived as this is driving me nuts (not to mention the 5 garages its been in )

1999 1.8 overheating problem? - mikej


did you ever sort your problem out?

Yes - as I mentioned above, I changed the thermostat and coolant and this solved my overheating problem.

I wouldn't muck about testing the thermostat, personally. It was only £12 IIRC and easy to change, on my 1.8i at least. If it has to be removed to be tested, then you might as well stick a new one in.

There is a lot of good info above in this thread and your problem may not be due to something as simple as a faulty thermostat though - good luck !

1999 1.8 overheating problem? - teek

hi mike i ve got the same prob on my focus 1.6, so far i changed new thermostat, new (cht), new water pump so prob, still presits, only on the moterway in high speed over 90-100mph but all i can say it all happens after i flush the coolant from the system, then i spoke to one of my friend( he is also machanic in toyota car company) this is what he said, start the engine and open the reservoire cap and while engine running just squized the bottom pipe of the radiater then i suddnely find the some air bubbles appears inside the tank , i did it for 10-15 min, and i had 30min run on the moterway for over 90mph and i found out temp metre stays on 12oclock position, so i think problem solve, but still i am waiting for very far distance to check and finalized.

1999 1.8 overheating problem? - RSKing

Hello, Just got a Focus 1.6 petrol

Its got a over heating problem

You can drive the car for a bit, then it just jump straight up to red, looks like the needle is sticking ? it was stuck on cold for a bit, then it went normal, then 10 mins driver jumped up , stopped the car, water was bubbling, so let some air out, it stopped the bubbling, even put the heaters on full, blast, when turned car off, then put the ignation back on, it jump up, then go back to 12oClock, bottom pipe is cold, all so the top pipe was cold, but after letting Air out top pipe went warm, bottom stayed cold, is it a themo stat ? or the heater valve ? hope its not the head gasket,

1999 1.8 overheating problem? - JonoH

I had the problem where my 51 plate focus was overheating on hills on the motorway.

I had a new water pump, temp sensor and thermostat fitted but no luck. My garage then fitted a new rad and flushed the cooling system as there can be a build up of crystalised antifreeze in the engine pipes that causes air blocks. This flush and the new rad sorted the problem at last!


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