The disappearing water trick... WTF!

Technical Area Engine, Transmission, Exhaust etc
2

 Clearly my little car has been taking lessons of David Copperfield. I fill up the expansion tank the next day it’s empty, no sign of where it’s gone, it’s just not there anymore!

To give you some background in October I fitted a new radiator as the old one had cracked along the top which was fair enough in a car this age, anyway no problems changing it and watched the water level like a hawk for about a week and it didn’t move an inch. All good.

Anyway fast forward to last wednesday, I’m driving the car into work and it’s taking a long time to blow hot air through the vents, which in this weather you notice kind of fast. So i look at the temp and it’s looking a bit higher then normal as in not in it’s usual place ie a bit before halfway but a bit further along, well i had been revving a bit hard in very stop multiple traffic light induced traffic, so didn’t think too much about it as it seemed to go down again and I was cutting it some slack anyway due to the weather. On the way home things got a bit more serious the temps were randomly shooting up then settling back down, and then at one point shot up got dangerously close to max and stayed there. Panicking as you do I pulled into a car park gave it some time to cool down and looked in the expansion tank. Empty, right so that explains it I thought, and silently berated myself. Luckily I still had some deionied water from the previous radiator change sitting in the boot, so I poured that in the expansion and then drove slowly to a nearby homebase (only place still open at that time) and picked up some more deionised water. Topped the tank off thinking right so that should it. Well it did sort of, temps on the way home where a bit better and when i got home I topped the tank off again and revved it for a while  (obviously it was drawing the water so I wasn’t worried). Then in the morning filled up the tank again as it was nearly empty (I hadn’t done this after revving it, as it was wet and raining), again I dismissed it as the car drawing the water in when I was revving it. Drove it into work and the temp needle did not move, big sigh of relief. Drove it home again and it didn’t move big sigh of relief again, then I checked the water in the tank… empty. Kicking myself again because I must have let it go so low for it to need that much water I poured another bottle into the tank (yes I overfilled it) thinking that should do it. At this point it had ‘drank’ a litre and a half of water, and had another liter in the tank. Anyway drove into work again this morning and again temps did not move but I just checked the tank on my lunch break (no time to check this morning) and it’s empty. Now seriously it can’t have drank a whole 2.5 litres of water, I think it holds about 5-6 anyway. So where is it going? Under the car is bone dry, and so is the engine bay.

(in case any of the astute readers are worrying about antifreeze levels by the way when I changed the radiator in October I put in a 50/50 antifreeze mix so seeing as 25/75 I’ve been told is fine I’m just I think diluting down the excess, not leaving it without anti-freeze entirely)

 

I’ve looked around and there is absolutely no sign at all of a water leak anywhere, and I’ve checked the oil dipstick and it’s clean also the car is running fine and not smoking popping etc etc so I don’t think head gasket.

Unfortunately what I haven’t been able to do is take the radiator cap off as the car has been hot each time I’ve had to check it, thats a job for this weekend.

Anyway I’m going to go over it with a fine tooth comb tomorrow but thought I’d open this up to see if anyone had any suggestions of things to check.

 

Thanks in advance, and sorry for the ‘essay’ :stuck_out_tongue:

 

3

When you replaced the radiator, did you fit a new Mazda radiator cap (not a pattern cap)?

4

Is this perhaps due to an airlock that has now disappeared, allowing the contents of the expansion tank to enter the main cooling system?

5

 With regards to the cap, no at the time cheap as they are and despite the recommendations I barely had 2p to rub together (bad month) so didn’t replace the cap as i had no reason to believe it was faulty, or at least decided to risk that it wasn’t faulty. Now I’m slightly more flush I was going pick up a replacement tomorrow just to be safe (it was on a to do list anyway). However I can’t see any sign of the current cap leaking, would I if it was?

 

As the for the air lock, I know there was no airlocks after the radiator change. However due to the temperature issues I would agree that there was an airlock but now the temps are stable I think this has now passed, unfortunately the water comsumption hasn’t. I suppose it could still have an airlock that it’s forcing out but that would mean the rad would have been practically empty! 

6

How odd. Some fluorescent dye and a UV lamp would be useful here. Could the water be dropping onto the exhaust and evaporating instantly? Are the carpets in the footwells under the dashboard damp?

7

 i have had similar issues with a discovery where the temperature gauge kept moving from normal running temp to the red section.  the result was the head gasket was broken allowing coolant to get into the cylinders which made the engine temperature get very high.  in theory this could also crack a weak radiator in the first place as it would be putting extra pressure into the cooling system

8

Well, this is interesting, a while back, I gave my Roadster a good thrashing to blow out the cobwebs, anyway as I was nearing home I noticed steam coming from under the bonnet, when I got home I found that one of the heater hoses had split, so I replaced all of my hoses with the silicone type, then on my next journey I still had steam coming fom under the bonnet and found that the radiator top tank had split, replaced the rad and all seemed ok on my regular four mile journey to work, but then on longer journeys my temp began to rise above normal (this was noticed after a period of a couple of months) returning to normal at tickover, I suspected a blockage so I fully flushed and backflushed the complete system, the water was foul. I also fitted a new water pump, radiator cap, thermostat and cambelt kit and checked the fan operation, still made no difference, also I should mention that when warm the exhaust has a strange smell which is hard to describe, and I also have a luke warm heater, so I also suspect that I may have a pinhole leak in the head gasket, another symptom is when I was burping the system EVERY time I revved the engine with the cap off huge amounts of water spewed from the top of the radiator almost emptying the system, this leads me to believe that the cooling system is over pressurising, I have now bought a HG kit and will be fitting it when the weather warms up a little bit. another thing is that the car uses a lot of fuel. I have been living with this for about four years cos the car gets me to work and back, but really it would have been better if the HG had failed completely and I would have replaced it. btw my car has only done about 60k

9

 IF your radiator is overheating for some reason you could be loosing coolant from the expansion tank overflow then when it cools down,  the engine sucks out what coolant there is in the expansion tank. Driving at speed you may not notice the steam coming from under the right side of the bonnet.

Another cause could be a pin hole leak that only leaks when the engine is hot and the coolant is under pressure. Check this out by looking all over the engine hoses with the engine still running when it has reached operating temperature. 

Another cause could be a corroded metal coolant pipe such as this one.      

10

 Well I spent a fair chunk of saturday looking at this and i’m potentially more confused then before.

I’ve now removed the radiator cap when cold and as it’s warming up and can there is a good level coolant and that it is flowing.

I’ve removed the expansion tank and looked for leaks and I can’t see any.

I had the car running for about 2-3 hours with intermittant drives round the block and no water leaked and the water stayed absolutely still in the tank, temperatures were fine (to clarify since the first time I refilled the tank the temp/heater issues have gone away).

After the above mentionned leaving the car to run I went out for about an hour (in the other car), checked it when I got back and the water level had dropped by about 30mm.

I then took the car out for another longer run and the water level in the tank was the same when I left compared to when I got back.

I then went to the pub, my fluid levels significantly increased.

Checked the water level in the morning and the expansion tank was empty, BUT there was a small puddle under the car, unfortunately it was under the belly pan drain hole.

Anyway now confused, a water leak while running I can understand, but a water leak that only occurs when stopped? Damn freaky little car…

11

Hi

That suggests water pump to me.  The seal leaks with no pressure (or very little pressure) but when the system is hot and pressurised the pressure on the seal forces the lips into closer contact with the shaft and hey presto no leak!  Mind you I could be wrong.

Alan

12

 No no I like that idea, it does make sense.

Hmm I might go and put some chalk round the seal and see if it disappears.

13

Also, when the pump is running and pulling water out of the the block the water pressure in the block will be lower than when the engine is stationary and heat soak is left to build up pressure in the block.

As I understand it, the genuine Mazda water pumps do not use a gasket. If the engine has overheated at some point and the water pump casting has warped then I guess this could allow water to leak out of the pump-to-block interface.

14

 

I agree{#emotions_dlg.thumb}i have hit this one before on an owers car,arn’t they great{#emotions_dlg.wink}

Regards

15

 Thought this one through a little more.

I only got the puddle when the expansion tank had water in it. I deliberately didn’t fill it this morning but just checked under my car on my lunch break and the floor was bone dry, no water under the car no raising temps suggesting enough water is still in the cooling system.

Getting tempted to just roll over and just hand it over to Freelance Mazda but that feels too much like a cop out.


Anyone know of an additive that I can add to water to give it a nice vividly traceable colour?

16

You can buy a UV tracer dye. Use a UV lamp/torch to reveal the source of the leak.

17

 It does sound like a head gasket leaking slightly into the cooling system, which is pressurising the system and blowing it out of the overflow pipe. You could put a container on the end of the pipe, see if coolant is lost there.

Otherwise as previously suggested, water pump or heater radiator, but you would have pretty damp carpets by now.

Mozza