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Coolant Pouring Out Despite Normal Engine Temperature

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I've recently bought a 1997 Ford Mondeo estate turbo diesel.

In normal cuising mode she drives like a dream. But put her idling or driving in low gear up a mountain road and within minutes coolant is pouring (and I do mean POURING) from under the engine by the right wheel (basically directly underneath the water pump?).

The odd thing is that the temperature guage by this stage is nowhere near the red...it typically starts when the dial reaches the letter 'o' in the 'normal' on the guage and the dial has never risen beyond even the half way mark.

Give the car tme to cool down either by switching the engine off or driving her downhill or picking up speed back to crusing speed (40mph plus) and the dial quickly drops back down again and the car stops leeking coolant.

I don't know much about cars but all the possible reasons that I've seen for coolant overflowing are the result of the engine overheating for one reason or another. So why is mine overflowing when the dial is nowhere near the red?

The only thing I can think of is that the guage is not working properly and the engine is far hotter than the dial is showing.

Or am I overlooking another possibility?

Any suggestions as to what may be causing the problem and solutions would be extremely welcome!


PS The coolant tank definately has no leak and I recently changed the coolant just in case there might have been a problem with the coolant itself (it didn't resolve the problem).

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When you start the engine the mechanical waterpump starts pumping coolant around the engine/ system, it comes out of the pump, and through the block, it comes out of the block and, before the thermostat opens, is diverted into the heater matrix, and back to the pump

so it does not go through the radiator -

untill the engine reaches operating temp, then the thermostat opens, and the coolant is allowed through the radiator, the collant temp drops untill the thermostat, closes- with the termostat opening/ closing, the correct temp is maintained, it is likely you have a leak on your radiator hose(s) that is why the temp stays normal (it will eventually rise if you loose too much coolant!) and it only leaks when the engine is up to running temp (when the thermostat opens)

Have a good look and you may see where it is leaking

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Thanks so much for that, FOCA mate!

A couple of follow-up questions to your reply:

1- How do I check the radiator hoses for leak? If I understood you correctly, there is only liquid flowing through the hoses into the radiator when the engine is running at operating temp. Assuming that is true, then I presume I have to first get the engine temp up and then have a close look at the hoses?

2- Assuming your diagnosis is correct, can I continue driving the car without causing serious damage to it even if the problem is not resolved as long as I make sure the engine is not over-heating and it is not loosing coolant? (The good thing is that I have figured out exactly at what stage on the temperature dial it starts to overflow and up till now have been making sure that as soon as I get near it I find some way to bring it down, either by stopping or by picking up speed if possible).

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Could the problem also be the thermostat for some reason is not opening up when the car is idling or going at slow sped, thus not allowing the coolant to flow into the radiator to cool down?

(I would assume that it is working properly when the car is at cruising speed because there is never any leakage or problem when it is running at cruising speed).

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It may be easier to find the leak once the engine is up to temp because you may be able to see where the coolant is coming from, but you may also be able to find the leak easily if there is a big gash in one of the hoses

You can run the car for short journeys, say to get it to a garage/ mechanic - if the coolant drops below a certain level the engine can overheat (due to poor or no coolant circulation)

if you are topping it up with tap water it can corrode the waterways in the engine, it can dilute tha anti-freeze, ideally, only the correct coolant should be used (it can be non-organic or organic- these cannot be mixed)

the proper stuff can be expensive - so it may be better all round to get your leak fixed kinda soonish (stitch-in-time, etc) :)

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Could the problem also be the thermostat that is not allowing the coolant to flow into the radiator to cool down?

No - this would not cause a leak

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Hi again mate,

I don't think she actually has a leak, it simply that the coolant is not being cooled down by the radiator, thus expanding with heat and overflowing.

I think I may have found out what the problem is. I ran the engine for about 10 minutes until she was plenty warm (temperature dial approaching the letter 'n') and the fan still hadn't kicked in.

It would make sense that if the fan is not working (or at least not kicking in early enough), the coolant would overheat at idle or slow speed, but be cooled down by airflow when the car is running at higher speeds.

Does that make sense?

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If i had the car in front of me i could probably tell in 10 mins what was wrong

Its important to stick to the facts, and not to jump to conclusions - for example assume that the temp gauge is wrong, it may be reading correctly, or it may be wrong - you cannot assume either way.

You must find out where the coolant is escaping - is it coming out of the overflow, or a gash in a hose

Is the radiator fan working? - again, just because you got the engine up to temp and it did not come on does not mean its not working - often, its a bit higher (typically 5-10 degree C) above operating temp that the fan comes on

Water boils at 100 degrees centigrade, under that temp, it does not boil/ expand, under pressure, water has a higher boiling point (about 110 degrees) the additives in coolant act to reduce the freezing point in the winter, and increase the boiling point in the summer

In my car, for example, i have special coolant that does not boil untill 138 degrees C (off the top of my head) at atmospheric pressure, the system is de-pressurised to put less strain on the (very expensive) electric racing pump/ seals/ system, the electric pump is electronically controlled, the system is unique on a road going Mondeo (as far as i am aware) - ive ran it without a radiator fan but the engine seems to stay cool (the pump is powerful enough for 4L/ 5L engines)

So you dont need to have a pressurised system but de-pressurising it lowers the boiling point and if you have diluted the coolant with water this my be your problem (but again- don't jump to conclusions)

IF the temp gauge is working it should go into the red before the engine overheats

I think the 1st thing is to find out exactly where the coolant is leaking from

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Your point about jumping to conclusions by an amateur is well taken, so let give you just the facts:

1- The liquid is coming out from somewhere around twelve inches to the left of the inside of the right front tyre

2- the amount coming out varies from steady drops to a torrent


4- As long as the temp gauge reading is below that, she does not spill a single drop. It does not matter whether she is idle or moving. I have checked this time and time again under lots of different circumstances and its always true

5- The temp gauge reading climbs to the 'o' when the engine is under strain e.g. going up a steep mountain road in 2nd or 3rd. The time it takes to get there can be very rapid or quite gradual depending on how hot the engine already is.

6- It also happens when she has been running for some distance and then I leave the engine idling (for example yesterday I'd been driving for about 30 miles and had to pull over to answer a phone call. I left the engine idling while I answered the call and by the time I had hung up (maybe 5 minutes later?), the gauge reading was up to the 'o' and had started dripping.

7 - The temp moves back down pretty rapidly when going back downhill or on the flat, or turning the engine off for a few minutes (although this last way is not as effective as getting greater windflow through the front of the car by going downhill or speeding up a bit on flat stretches)

8- On good quality roads where the car can cruise at a steady speed, the temp gauge reading goes nowhere near the 'o' and she does not leak. On Monday even after I had driven 400 miles on good roads at 60-80 mph the gauge reading hardly got as far as the 'n' and the coolant level had not dropped at all.

9 - I am in Spain and the weather has been stinking hot.

I spoke to one mechanic who seemed to think there was nothing terribly wrong. He said all the symptoms are simply of the coolant overheating and being flushed out as it expands. I can totally get his reasoning, I am simply confused as to why its happening when the temp gauge reading is nowhere near the red!

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Its very easy to jump to conclusions, both amatuer and professional - i read it all the time on forums, classic ones are people replacing perfectly good sensors when they gave a faut code read and they assume the sensor is at fault - in your case, we cannot assume the temp gauge is correct, or wrong

Is the coolant level dropping?

Are you topping up the coolant, and with what?

Have you ever seen the radiator fan come on at all?

could you post up a picture of your temp gauge, as i have no frame of reference - its a pity we do not know the actual temp, - an electronic fan controller could give you an exact coolant temp, in C, + an adjustable temperature control for the fan

A live OBD feed with temp in real time would also help (does it have OBD1?)

a diesel can run quite hot, like 95 degrees centigrade, this is obviously close to the boliing point of water, (100 degrees centigrade) with the hot temps in Spain it can put the cooling system under a lot of strain

Perhaps there is not much wrong with it and a flush of the old coolant and replaced with new, higher-performance coolant (with a higher boiling point) or fitting an electronic thermostat to the radiator fan and have it come on at a lower temp, or fit a thermostat that operates at a lower temp, or vent the bonnet (ive removed the rubber seal at the back of my bonnet- works really well as the engine bay can act as an oven, otherwise) or a mixture of these things

Another tip - take coolant with you to top it up - just in case - i used to use Tesco bottled water at 17p for 2 litres as it was cheaper than distilled water - but as before- be careful of diluting the coolant

the radiator relies on a temperature drop - the colder the ambient temp is, the greater the drop, (or temperature difference) and the better it works, in high ambient temps the radiator can not work so wel - if heatsoak is taken into consideration, in extreeme enviroments the radiator can get so hot it stops cooling the engine ie- if the engines operating temp is 95 degrees and the radiator reaches 95 degrees it cannot cool the engine -

Slot vent- the slot vent in the back of the bonnet acts as a chimney, heat rising and escaping out the back, this is replaced with cool air coming in the front, even with the car stationary, with the radiator fan off ( the vent prevents a reverse=flow, where the heat (even hotter) radiates forward (the wrong way) ) and the underbonnet temps escilate due to the high engine core temp with nowhere for the heat to escape exept back out the radiator, making a "viscious cycle"

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With regards to point of reference, sorry I have been a bit presumptuous! When I talk about 'o' or 'n' what I am referring to is the temp gauge on my dash board which has a white block, then the word 'normal', followed by a red block. When the dial is on white, obviously the engine is cold, when on the red block, overheated. The 50% mark is between the letters 'r' and 'n'.

As I said before, the coolant starts leaking when the dial is pointing at the letter 'o' i.e about a third of the way to overheated/red.Until then, she is steady as a rock and doesn't leak a drop, no matter how long I drive.

It therefore seems that only under very specific circumstances (such as going uphill in low gear) the coolant is getting too hot way before the actual engine temp is.

I always make sure the coolant level is ok ever since I first discovered 10 days ago there was almost none left in the tank! (I've been mixing it up a bit and at the moment she's a bit over-heavy on the coolant but I'm basing that on the idea that she will probably start over-heating again the next time I go up a steep mountain road and will need to add more water)

All your tips are really handy and useful as basically I have found no problems with the actual performance of the car - she actually drives very, very nicely, with no nasty noises or anything coming from the engine or any other signs that she is not coping. But using your tips to keep the coolant from overheating are all great to know!

I'd also like to thank you for taking the time and patience for all your informative replies, they really are appreciated, mate!

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