350Z Coolant Disappearing Act

[Alias218]

Hi all. Now this is a little embarrassing, given my job and having been trained as a mechanic in my apprenticeship.

However, I went to bring my 2007 350Z out of its annual slumber and noted the degas bottle was empty. This means approximately 800ml of coolant has disappeared since last October with the car only being run briefly on a couple occasions.

I’ve checked all the usual suspects - coolant on ground or undertray (nope), degas bottle (no cracks), top hose (dry), bottom hose (dry), the radiator (sound and is still full), other hoses/pipework around the engine (dry).

There was a little misting around the stat housing, but this was old and filthy black with accrued dirt. This I have cleaned and is my no. 1 suspect at the moment, though there are no signs of lots of coolant coming from there or running down the front cover.



The only other suspect is the water pump which has two o-rings. If the inner fails, coolant can leak from a pinhole in the block. If the outer fails too, coolant can run behind the front cover into the sump. But this only happens when the engine is running. In any case, the block was dry and I’m going to drop a little oil tomorrow to check for coolant (the dipstick seemed OK).

It isn’t head gasket related as the engine hasn’t run for more than about 20 minutes in 6 months.

TL;DR: I’ve lost nearly a litre of coolant and can’t find where it’s come from!

If anyone might have any other suggestions, perhaps specifically for the VQ35HR found in late 350Zs, then I’m all ears! Beyond this, it’s top her back up then suck it and see.

[stevieturbo]

Exactly what are you calling a "degas bottle" ?

it is not a commonly used term

And you seem to be suggesting this coolant disappeared, while the vehicle was sitting, and not actually in use ?

Simple way to look for leaks, pressurise the system and look, and see if it does or does not maintain the pressure.

Or drain it and use a smoke machine and fill it up, again to a sensible pressure, say 15psi or so, or indeed higher.

[Alias218]

Sorry, work term. Coolant reservoir / header tank - call it what you will.

Yes, that’s exactly right. It’s been sat and the coolant has seemingly vanished into thin air. There is absolutely zero trace of it. This isn’t a complicated cooling system so there really aren’t many places for it to go.

I did think about pressuring the system, though I don’t have a kit to hand so will be on the to do list once I get hold of one.

I’m rather hoping there’s something elementary I’m missing here. A leak this big should leave a trace.

Edited by Alias218 on Saturday 8th April 19:47

[stevieturbo]

Alias218 said:

Sorry, work term. Coolant reservoir / header tank - call it what you will.

Yes, that’s exactly right. It’s been sat and the coolant has seemingly vanished into thin air. There is absolutely zero trace of it. This isn’t a complicated cooling system so there really aren’t many places for it to go.

I did think about pressuring the system, though I don’t have a kit to hand so will be on the to do list once I get hold of one.

I’m rather hoping there’s something elementary I’m missing here. A leak this big should leave a trace.

Edited by Alias218 on Saturday 8th April 19:47

Again, clarity....so this is the pressurised header tank ? Not an expansion or overflow bottle ?

So the main system has actually lose fluid ? Again, just do the basic tests.

It may be leaking externally, internally, or maybe it's nothing at all.

[Alias218]

It’s an overflow tank rather than expansion, however the distinction is moot in this instance as the system hasn’t been under pressure for a long time.

I was rather hoping there may have been a quirk of the VQ that I was missing but it seems not.

I’ll have to get a testing kit on order and see if that shows anything up.

Thanks.

[Dave.]

Is it totally empty, as in dry?

We had mice chew through the overflow pipe from the cap to the tank over winter, thankfully they did it high up so we didn't lose any coolant.

[stevieturbo]

Alias218 said:

It’s an overflow tank rather than expansion, however the distinction is moot in this instance as the system hasn’t been under pressure for a long time.

I was rather hoping there may have been a quirk of the VQ that I was missing but it seems not.

I’ll have to get a testing kit on order and see if that shows anything up.

Thanks.

It's not a moot.

If it is a vented bottle outside of the pressurised system, there is simple scope for evaporation if left sitting. Assuming the level in this external bottle is what you are sure it was back whenever.

Clearly if it is within the sealed pressurised system, then evaporation should be impossible, and it can only be an internal, or external leak.

So if it is in the pressurised system you think you have a leak, basic first step is pressurise it and see what happens.

The photo image you show is of a hose/clip that would be part of the pressurised side of things

[E-bmw]

The other obvious place to check is in the cabin as it can leak from the heater matrix into the cabin and be felt/seen under the carpet.

[Alias218]

stevieturbo said:

Alias218 said:

It’s an overflow tank rather than expansion, however the distinction is moot in this instance as the system hasn’t been under pressure for a long time.

I was rather hoping there may have been a quirk of the VQ that I was missing but it seems not.

I’ll have to get a testing kit on order and see if that shows anything up.

Thanks.

It's not a moot.

If it is a vented bottle outside of the pressurised system, there is simple scope for evaporation if left sitting. Assuming the level in this external bottle is what you are sure it was back whenever.

Clearly if it is within the sealed pressurised system, then evaporation should be impossible, and it can only be an internal, or external leak.

So if it is in the pressurised system you think you have a leak, basic first step is pressurise it and see what happens.

The photo image you show is of a hose/clip that would be part of the pressurised side of things

It is moot as it hasn’t evaporated IMO. If it had the glycol would have left some sticky residue if the glycol would have evaporated at all in that time, plus I have over-wintered this car for the last 7 years and the level has never dropped. The bottle was clean as a whistle inside, which says to me that this was a fairly fast loss of liquid. I’ve seen enough evaporated glycol to know that it leaves a residue.

The photo I posted was simply to show the stat housing where I found the most evidence of wetness. But it’s not heavily soiled to the point I think 800ml of fluid has leaked from there.

Edited by Alias218 on Sunday 9th April 10:52

[Alias218]

Dave. said:

Is it totally empty, as in dry?

We had mice chew through the overflow pipe from the cap to the tank over winter, thankfully they did it high up so we didn't lose any coolant.

Completely dry save for a small puddle at the bottom.



From what I can see, all hoses are sound.

Edited by Alias218 on Sunday 9th April 10:55

[Alias218]

E-bmw said:

The other obvious place to check is in the cabin as it can leak from the heater matrix into the cabin and be felt/seen under the carpet.

Thanks, I forgot to mention that I checked the carpets and they are dry (thank goodness!).

[stevieturbo]

Alias218 said:

Completely dry save for a small puddle at the bottom.



From what I can see, all hoses are sound.

Edited by Alias218 on Sunday 9th April 10:55

That is simply an overflow.

Water can get ejected into it, and should get drawn back into the main system as it cools

If there is a leak inside the cabin, often yes it can be hard to see....but not so hard to smell, and windows would tend to steam up a lot too.

But again, basic first steps, pressurise the system

[Alias218]

stevieturbo said:

That is simply an overflow.

Water can get ejected into it, and should get drawn back into the main system as it cools

If there is a leak inside the cabin, often yes it can be hard to see....but not so hard to smell, and windows would tend to steam up a lot too.

But again, basic first steps, pressurise the system

Thank you for your help, but I know that’s an overflow - I’ve already stated as much. And I know to pressurise, however, (again as already stated) I don’t have a kit to hand to do this yet.

There’s no smell of glycol in the cabin, and it is perfectly dry.

Just for background, I work for a large OEM so I do know my way around a car. I’m asking for help because the evidence I have in front of me doesn’t lead me to draw any conclusions so was after alternative ideas.

[anonymous-user]

Start the car up, get it up to temp and see if the coolant reappears in the tank.