Mysterious coolant loss, any ideas?

[Ahead]

Background: Bongo doesn't get much use, use her to tow the race car to meetings and occasional holiday. Approx 6 months ago it lost a litre or two of coolant, almost overnight. Topped up and re-bled and had been more or less fine up until now. Bongo has both low coolant and Mason alarms.

Used Bongo for a week holiday from Hertfordshire to Lake District and back, including crossing Hardknot pass in the wet (!). Checked coolant when I got back and level was fine. That was a week ago, not used Bongo since, but jumped in it today, went to start it and the coolant alarm kept screaming..... Popped the bonnet and found the header tank empty. Removed the air intake and took off the rad cap, needed about a litre in there + the header tank. Have re-bled system.

No obvious leaks anywhere and what I don't understand is level was fine last time I checked, didn't use Bongo and suddenly I've lost 2+ litres??

Any ideas guys?

[Northern Bongolow]

most of the unexplained coolant losses i see are either the exp tank cap or the water pump.

scenario 1
the cap leaks pressure below the stated 1.1 so it leaks when working hard, this lowers the boiling point and lets the coolant amount expand. so when warm, the coolant level seems fine, until it cools, then is found to be low. fit new mazda cap.

Scenario 2
the water pump seals leak, but only when cold and the system is unpressurised.
when cold and relaxed the pump leaks for 15 -30 seconds, then as the heat and pressure inside the system increases this stops the leak.
if its a diesel or v6 they both have 2 holes in the pump casting, 1 at the 10 past position and 1 at the 6 oclock position. they usually leak from the 6 oclock position hole, this is very hard to detect as its hidden from view, i use a angled head dentist mirror, and can sometimes see a clean line made by coolant on the casting.

neither leak shows on a pressure test.

[The Great Pretender]

So, where did the coolant go......................?
Due to the run you did and the position of the Bongo stat, it probably boiled in the head and dumped it out of the tank keeping it full, then when the system returned to negative pressure it pulled the coolant back. If the Bongo had a proper expansion tank what you had lost would have been drawn back into the system by pressure differentials.

[dave_aber]

I've just swapped my waterpump due to that very leak. I added UV due to the system, then got in with a UV torch - and there was a tell-tale yellow line running down from the waterpump.

I was only losing 100ml or so though, every week, approx.

Having done the work, I have also discovered that I have a weep from the radiator. The original one failed about 18 months ago, with a weep from the top where it's crimped together - this time it's the same issue, but at the bottom.

With the new waterpump, the van is running 3-5°C hotter at the head too, which is odd, and unexpected.

[mikeonb4c]

I've just swapped my waterpump due to that very leak. I added UV due to the system, then got in with a UV torch - and there was a tell-tale yellow line running down from the waterpump.

I was only losing 100ml or so though, every week, approx.

Having done the work, I have also discovered that I have a weep from the radiator. The original one failed about 18 months ago, with a weep from the top where it's crimped together - this time it's the same issue, but at the bottom.

With the new waterpump, the van is running 3-5°C hotter at the head too, which is odd, and unexpected.

Interesting. If I'd had to guess, I might have said a less efficient radiator was more likely to cause this. But, thinking about it, maybe a less efficient pump is the more likely cause. You sure its the pump change that coincided with temp rise?

[dave_aber]

Yup, the head until last week was always around 86°-89°, only going into the 90's under load - going fast uphill etc.

First drive with the new pump - sitting 89°-94°, going up to about 99° under duress. Drops back quickly when you ease off, so everything is as it should be. I was concerned that it wasn't fully bled, but the level in the tank hasn't dropped overnight, and both heaters are working OK, no boil-ups, no gurgles, etc.

The only things changed are the pump and the coolant. As far as I can remember, I've used the same brand / type of coolant.

It'll be getting a new rad and re-bleed in a few days, so we'll see then.

[Ahead]

Cheers. New pump is on order and should be with me tomorrow. I had suspected the pump as the last time there was a sudden drop, I'm fairly sure I could see a wet patch under the centre of the van although I couldn't see where it might be leaking from. I've got the bleeding off pat now, hopefully the pump replacement itself is straightforward...

[rita]

Yup, the head until last week was always around 86°-89°, only going into the 90's under load - going fast uphill etc.

First drive with the new pump - sitting 89°-94°, going up to about 99° under duress. Drops back quickly when you ease off, so everything is as it should be. I was concerned that it wasn't fully bled, but the level in the tank hasn't dropped overnight, and both heaters are working OK, no boil-ups, no gurgles, etc.

The only things changed are the pump and the coolant. As far as I can remember, I've used the same brand / type of coolant.

It'll be getting a new rad and re-bleed in a few days, so we'll see then.

Would the Hot Weather in Scotland in the past week not have a bearing on the rise of your engine temp.??

Just a thought.

[dave_aber]

It crossed my mind today driving to aberdeen in the scorchio weather, it may be a factor. It does seem more sensitive to a thrashing.

[Northern Bongolow]

mine did the same when i swapped mine during the winter----2 deg rise . the only thing that occurred to me was the number of blades on the pump, the replacement had more blades but smaller ones. the same type of coolant was put back in.

this 2 deg in mine seems insignificant on the one hand but then this also increases the running pressure,as its already running at 10-11 pounds when thrashed this brings it near to the fan trigger temps,again not a problem in a good system but my rad is an old one my fans trigger at 12-13 psi
think a gen mazda pump maybe on the to try list (when ive saved up enough).

is your egr blanked dave ??

[Ahead]

I've bought one on eBay.... Will check the number of blades. I didn't know the fan cut under pressure? Might this explain why occasionally I hear a fan even when the engine's cold.

[The Great Pretender]

It is worth checking the impeller to body clearance on the old and new pumps; the clearance needs to be minimal. Running a higher temperature with a new pump suggests the impeller to body clearance is to large, slowing flow leading to the higher temperatures noted.

[dave_aber]

I didn't compare the pumps, should have really.

EGR is blanked

I'm going to re-bleed it to be sure.

[dave_aber]

For reference :

My comments on pump replacement -

Working from under the passenger's seat:

1. Disconnect the -ve lead from the starter battery.
2. Crack / Slacken the 4 bolts holding the pulley on the pump before removing the belts.
3. Remove the wiring from the alternator
4. Slacken the alternator bolts, and adjust it right in to slacken the 2 belts
5. With the Pump / Alternator belts slack, you can now access the AC pump tensioner.
6. Slacken the 17mm nut on the AC tensioner, then loosen the belt using the 12mm bolt on the top of it.
7. Remove the AC belt, then the Water / Alt belts.
8. Remove the alternator
9. Remove the 4 bolts holding the waterpump pulley on.
10. Remove the pulley - might need a tap / lever etc.
11. Remove the 2 nuts, 5 long bolts and 1 short bolt holding the pump in place. Note the position of the short bolt.
12. Remove the pump. Obviously you'll drop the coolant at this point, unless you have previously drained it.
13. refitting is the reverse of removal.
14. Bleed the system etc.

You'll end up with a scratched left arm.

[Northern Bongolow]

It is worth checking the impeller to body clearance on the old and new pumps; the clearance needs to be minimal. Running a higher temperature with a new pump suggests the impeller to body clearance is to large, slowing flow leading to the higher temperatures noted.

cheers for that mel. too late for me to check mine also as its gone to the scrap man, ive got several old ones lying around though including muzzes million mile'r so i will have a go compare