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Mondeo MK4 Heating issue / coolant loss

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Hi all


These forums have been a real help so far and now am hoping someone is able to help me.


My Mondeo MK4 2009 1.8 TDCI suddenly overheated last week after a loss of heating inside the cabin.

I was towed home by RAC and then had a mechanic come and look over the car.

He replaced the coolant expansion tank, thermostat and also did a complete flush of the cooling system.


Got the vehicle back yesterday and unfortunately it's still doing exactly the same thing.

Heat inside the cabin all fine, engine heat ok... then all of a sudden freezing cold inside the cabin and engine temp rapidly rising.


I opened up the bonnet and i believe that the leak which is quite rapid is somewhere at the back of the engine below or from the heater matrix.


Anyone have an ide what the cause may be?



More info on the mechanic's analysis.

he found that the EGR cooler at the back of the engine had been bypassed by previous owner possibly.

The two pipes had been joined together rather than allowing coolant to flow through the cooler.

He also discovered that the rocker cover's gasket had a leak, which he's going to fix in a couple weeks time.

He checked the coolant to see if there was sign of the headgasket gone, however he said that his test came back negative.

He said the water pump is working and not leaking.


Please let me know if anyone has any idea what the issue may be.

I'm probably calling up Ford tomorrow to have the car booked in...  :(












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23 minutes ago, beastymantis said:

I opened up the bonnet and i believe that the leak which is quite rapid is somewhere at the back of the engine below or from the heater matrix.

The coolant path at the back of the engine is from the back of the cylinder head, through the EGR cooler, through the cabin heater, through the oil cooler, then back across the bell housing (under the airbox) to the inlet pipe to the water pump.

Water leaks into the oil cooler would cause severe emulsification of the oil, with grey gunge in the oil filler cap and crankcase breather hoses. Water leaks (unless tiny) through the heater would give a smell of antifreeze in the car, and sodden carpets.

Bypassing the EGR cooler seems complete lunacy. I can not see a blanking plate in the EGR inlet port (normal place). If it is not blanked or mapped out, then hot exhaust gas is the last thing anyone would want in the EGR valve or in the engine intake system. Maybe the cooler had a leak. If so, I hope the valve was blanked (somewhere) or mapped out.

I guess the car is loosing coolant. Detecting the leak is a process of elimination. Keep putting anti-freeze in, it is good for the engine, and helps identify leaks by smell and dried residue. Cardboard sheets in strategic locations are useful, I found a coolant tank leak that way. The water must be going somewhere, either leaking out as water, or as steam in the exhaust.

I would put off going to a Ford dealer for as long as possible. They have set routines to follow, usually involving replacing lots of expensive bits. The quality of Ford franchised garages varies enormously.


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thank you so much for the reply.

I'll definitely hold off sending to the Ford garage up the road.

will however get back in touch with my mechanic and advise what you have said.

he had mentioned that the EGR cooler at the back of the engine should be connected etc, so will get him to buy the right pipes etc.


as for the rapid leak of coolant, finding where this is coming from is proving to be difficult.


and £20 for 5l of coolant from Halfords is starting to get expensive :(

bought 4 already and got half of one remaining.

I assume my mechanic has not got the right tools to pressurise the system to locate the leak hence why I thought of going to Ford.

its the sudden loss of cabin heating that gets me confused. As soon as the cabin air goes cold, the engine temp starts rising. And there's coolant all in the engine bay and steam rising from the back of the engine somewhere low down.


ive not checked the oil cap myself, but will do so in the morning to check for what you mentioned.


reading through your explanation of the flow of coolant, could it be just a hose? Or possibly something worse like where it goes into the engine for oil cooling etc?



Don't by any chance know someone in Bury st Edmunds who Is specialised that I could take this to?


Let me know if you want any other photos - the attached ones were from earlier this evening when I took it for a test drive and experienced the overheat.


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1 minute ago, beastymantis said:

its the sudden loss of cabin heating that gets me confused. As soon as the cabin air goes cold, the engine temp starts rising

The outlets from the cylinder head to the heating system, and to the thermostat and radiator, are quite high up on the cylinder head. If the coolant level falls below this height, and air gets in (or steam if the engine is warm), then circulation will stop, and the heater will go cold, while the engine will overheat.

As a totally irrelevant bit of nostalgia, I have memories of driving a Hillman Imp, notorious for cooling problems (among many others!), gloves and coat on in the freezing car, with steam coming out of the back from the boiling engine.laugh.png

Hopefully it is just a hose. It should not take too much ingenuity to rig up a way to pressurise the system, using a tyre pump or similar. One of the little vent hoses that return to the expansion tank (if it anything like a Focus), would be my first target. They are quite easy to couple other tubes or hoses up to.

It sounds like a pretty major leak, it should be having visible consequences somewhere. If that much water was leaking into the engine, or through the heater, you would notice it. If it was the head gasket, there would be a lot of white smoke from the exhaust.


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  • 1 year later...

Clean it up, dry it out, then top her up and watch what happens, get it all warmed up and flowing through the radiator as well. without knowing the engine its a little tricky to point you in the right direction but the principle is the same as the above advice on most cars. coolant will go through an Oil cooler, EGR cooler, thermostat (and thus radiator) heater matrix and the engine block itself. there will be pipes all over the place linking this together. To satisfy your mind check the oil, look for white mayo. but its probably a cracked hose or failed clip the heater matrix was notorious on the Focus, I dont know if that's the same on the Mondeo

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  • 1 month later...


Can any one explain what the part connecting from the engine to the hose that goes to the top of a radiator is called (not hose but the actual parts that touch) and how to repair a coolant leak from this.


It's a mk 4 mondeo 2010 1.8 TDCI

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7 hours ago, Kranist said:

the part connecting from the engine to the hose that goes to the top of a radiator

The top radiator hose links up to the engine at the thermostat housing. Not easy to repair, but widely available as spares.


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  • 4 months later...
On 10/13/2018 at 8:22 PM, Joe65 said:

Any one actually cured this problem???

Mine is doing exactly the same. Allready done waterpump and head gasket.

Coolant leaks are quite common. There are so many places it can leak, but almost all will leave some trace or sign. It is a matter of going through every possibility. Hoses first, I had one of the small vent hoses burst near the expansion tank recently. There are lots of water hoses, but leaks usually will be visible. Wrapping some cloth round a suspect area might help detect small leaks.

Then expansion tank. I also had this about 4 years ago, and detected it by placing cardboard under the tank. It got wet & smelt of anti-freeze.

Heater matrix will always give a smell of anti-freeze in the cabin. Main radiator is harder, but visible deposits on the radiator is the usual sign. EGR cooler and Head gasket will both give white smoke in the exhaust when idling after a run long enough to get to full temperature. A faint smell of anti-freeze in the exhaust should also be detectable. Oil cooler will cause grey emulsion in the engine, especially inside the crankcase vent hoses.

See 6 June 2019 below for two more possible leak areas.

I am not sure what your engine type is, this thread relates to the 1.8TDCI, but most items will be common to other engines. Head gasket leaks do not seem common on this engine, unless maybe wrong or no anti-freeze was used, allowing corrosion.

Edited by Tdci-Peter
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  • 5 months later...
  • 2 months later...
On 3/26/2018 at 11:19 AM, fridgesparl said:

Hi I'm new to the forum my mondeo is doing something similar did you ever get it sorted changed the pump running with no thermostat to rule that out still no luck



On 3/20/2019 at 12:29 AM, Dylanrmay said:

Ever fixed..?  Same problem same car , car is dropping water


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13 hours ago, Sandsjason said:

But no leak and car not overheating  someone said headgasker.

If it is a 1.8TDCI, then headgaskets rarely go unless the engine has been badly overheated, so that goes down the list a bit.

I covered most of the leak areas in my post above on Oct 14, 2018, but two items I forgot to mention were:

The lid for the expansion tank. If this is damaged, then you can get a very slow drop in coolant which leaves no trace, due to evaporation.

Water Pump: This is just above the crankshaft pulley at the timing end of the engine. It can leak from the seals, and water deposits may be visible below it. It is largely hidden by the timing belt cover. Viewing (with a torch) should be possible from below or maybe via the wheel arch with the wheel removed.

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  • 3 months later...

Ford Mondeo mk4 / 1.8 tdci / 2007 / 150 hp (1st stage tuned)

Hi all,

Since last year I own a Mondeo with above mentioned specs. The person (a colleague from work) I bought it from never encountered issues I am about the mention. 

A few months ago I had to change a hose that caused a huge leakage and as a result an overheated engine. After the repair the cooling system started building high pressure (hoses were extremely hard) and cooling fluid loss occured (each 300-500 km 0.5 litres).

A Ford mechanic who is repairing cars outside his regular working hours checked it and told me it must be the cylinderhead that got damaged because of the overheating. A repair (revision of the head) would be the cure. I took a risk and drove to Turkey this year for our summer vacation, which is about 3000 km from The Netherlands (my home country). Nothing happened, besides having had to refill fluid every 700-800 km. Worried about the return trip I decided to do revision in Turkey and brought the car to a Ford service there. Both the head as the block got machined. 

The car brought me back home but I still had to refill fluid and it got even worse (I returned a month ago and since two weeks the leakage got worse). I am filling 1,5 liters of fluid, meanwhile only water, every 50-100 km. 

I went to the same mechanic who advised the repair a few months ago, and he nailed the coffin by telling me the engine needs to be replaced or I sell the car. The water is supposedly leaking through the exhaust caused by a ripture in the block. 

I wonder how this is possible, that amount of water should be visible as smoke from behind but the mechanic tells me it vaporizes, which I refuse to believe. I read through lot’s of posts but I’m clueless. See this as my last sprinkle of hope.

Can anyone help me and tell me there is still something I could think of?


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1 hour ago, Engin said:

do revision in Turkey and brought the car to a Ford service there. Both the head as the block got machined.

It should have been evident when the head was removed if there was a gasket leak. It would be odd that they machined the surfaces if there was no evidence of a leak. It also seems a bit unfortunate if there was both a gasket leak and a cracked head or block.

It is possible something went wrong with the machining, and the surfaces were not quite flat. Also they would have to use an extra thick gasket to maintain the piston to head spacing, which is very tight in the 1.8TDCI. So this is another area where it could go wrong.

If it is not the gasket, then a leak to exhaust is more likely to be a crack in the cast iron head than the block. It might be possible to get a 2nd hand head. Removing the head again will tell if there is a gasket or crack problem, to an experienced & watchful eye at least.

Filling with anti-freeze mix (use the cheapest stuff if you like) will help identify if the leak is to the exhaust, by the smell. A small leak will vapourise in the hot exhaust area. Since a diesel engine like the 1.8TDCI has no throttle, a lot of air passes through even at idle (lean burn). This high airflow can prevent the water from condensing back to visible "steam", which is actually a mist of water droplets in air or gas. In a petrol engine, the throttle gives a much lower air flow (stoichiometric mix), and the condensation point can be reached with a correspondingly lower amount of water added, made more apparent by the water from the burnt fuel. So, especially in warm weather, a fair sized leak may not give visible mist with a diesel.

If tests elsewhere: in the oil, under the header tank, in the footwells, around the hoses, radiator and pipes, reveal no leaks, then the exhaust is the only other exit for the water.

An EGR cooler leak can also leak coolant to the exhaust, but this does not really tie up with the overheating, so is less likely.

I can not think of any leak paths from cylinder block to exhaust. A replacement head is not as bad a job as a replacement engine!

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Hi Peter, 

I am truly impressed by your expertise. I called another mechanic this morning and he also referred to the egr cooler if not the gasket, head or block. As the overheating in the beginning was a result of instant loss of water due to the ripped hose, I desperately want to believe it's the egr cooler. Do you have any tips on how to have that checked? In the meantime I am already searching for cylinder heads in case I have no other option. Thanks a lot for your help.

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4 hours ago, Engin said:

I desperately want to believe it's the egr cooler. Do you have any tips on how to have that checked?

I doubt if there is any way to check whether the leak is exhaust port to coolant inside the head, or the cooler, except by removing the cooler and pressure testing or internally inspecting it. The EGR cooler is directly connected to the exhaust port.

If it is a crack in the head, and there is no grey emulsion in the oil, then my guess is that it is in the area between the exhaust valve and the manifold connection. The casting will be rather complex in shape here, and thinner walled than on the cylinder side of the valve, so more liable to expansion cracking if operated without coolant.

Thinking a bit more about the EGR cooler, it gets the same hot gas as the head, and is designed to stay full of water in its jacket. The welds at the ends will create high stress areas, hardened steel, and possible erosion or corrosion areas. So it is worth getting it out for a good look, I would say. The Lynx (1.8TDCI) engine is usually renowned for toughness, so you may be lucky!

Have you looked for the tell tale grey emulsion, most likely to be up inside the cam cover, or inside the crankcase ventilation hoses. A leak between the coolant jacket and a cylinder will usually form this emulsion as water seeps into the cylinder, and gets past the pistons into the sump. A leak direct from coolant jacket to the exhaust (in the head or in the EGR cooler) is less likely to form this emulsion.

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Hi Engin, have you had a sniff test on it? This detects if there's exhaust gases getting into the coolant due to a head gasket failure.. The kits can be bought quite cheaply on ebay and all good garages should have one anyway. 

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  • 7 months later...

Ford mondeo 1.8tdi 2008 

It seems like my car is overheating but the exspation tank seems to get to hot and coolent just seems to shoot out the bottom of the tank 

Iv had a new thermostat also tried steel as steal but I didn't think it was the head gasket anyway can any body help please 


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I had a similar issue, losing coolant. I was aware of a small drip from the thermostat housing, too small to be of consequence. Turned out to be the expansion tank cap. Firstly it needs to be screwed down, keep turning, it's firm, then it clicks it's done. Secondly, it's a pressure cap and they do fail. When they do the coolant can come out of the overflow to the front, or commonly, look at the raised ring around where the cap goes. At the back it is cut out to allow anything coming out or spillage. Anything coming out due to a failed cap goes this way and is blown by the air making it look as if there is a leak at the back of the engine. Buy a cap. For what they cost it is cheaper if it solves the problem. Good luck.

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  • 6 months later...

Has anybody had this issue resolved? Iv got the same issue with my Mondeo edge 1.8 tdci, looses cabin heat and looses water, which results in engine overheating, iv had it to the garage up to now spent £600 it's had timing belt, wet belt, and water pump change, water header tank change, then had new thermostat and hose, and yet it's still doing this, any advice would be greatly received, as we honestly haven't a clue. 

Edited by Matthewb91
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  • 3 weeks later...
  • 1 month later...

Have coolent leaking from expansion tank when engine warm mondeo 2010 1.8 d Zetec. Done thermostat coolent flush new tank and cap still backing up pressure any ideas


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