Katy Perry syndrome

[Calps]

Suggestions/opinions welcomed on a root cause/causes of engine overheating issue please. Bonus points if there are steps I can follow to rule something in/out.

Context: My car has been sorn'd since last November. It's been sat at the side of the house, under partial cover for the time, started once a week, run for ~15 mins, warmed up, and move back/forth to rotate the tyres.

All was well when it was sorn'd, and during that time things seemed normal with one exception - it's developed a Katy Perry personality, blowing hot & cold (see what I did there). Once the engine had warmed up, I'd turn on the heater to run some warm air throguh the cabin. Initially there would be a blast of warm air (max 10 seconds worth), quickly followed by a return to cold air, and stayed that way.

I didn't pay too much attention to it, but whilst bringing it for its NCT (Irish MOT equivalent), the temp gauge went into the red after ~10km, and I had to pull over. This happened twice on the trip home. It didn't run for very long in the red zone, so I'm hoping there was no/minimal damage done.

Inspection of the engine bay showed some coolant had gotten out. I topped it up, and it's remained full since (albeit only driven ~5km, and then on/off my driveway since), so hesitant to declare that there is a leak.

The water pump appears to be working (a slow, steady flow of coolant can be seen entering the expansion tank when the cap is removed).

If any knowledgeable folks could suggest potential issues (ideally which I can triage myself, but not a dealbreaker) that would be greatly appreciated. I may have omitted some useful info from the above, so happy to answer any Qs that might add additional clues.

Thanks!

 

[dhobbs]

I assume you have the n52 engine as your profile image is a coupe, that would point in the direction of the water pump being intermittent. They do seen to play up a few times before giving up for good. Not sure if they give any codes to be honest.
Do you know if it's the original pump?

 

[enuff_zed]

I didn't pay too much attention to it..........................

Inspection of the engine bay showed some coolant had gotten out...........................

Did you ever check the coolant level in the expansion tank?
Is it possible there was a small leak, maybe due to seals drying out, and that has caused an airlock due to low coolant level?

 

[Calps]

I assume you have the n52 engine as your profile image is a coupe, that would point in the direction of the water pump being intermittent. They do seen to play up a few times before giving up for good. Not sure if they give any codes to be honest.
Do you know if it's the original pump?

Correct - N52 3.0si alright. No codes showing, but like you suggest, I don't think it throws any codes beforehand. I believe it's the original pump (no record of it being changed), and as luck would have it I had already bought a replacement (Pierburg), just not gotten around to fitting it. The pump was my initial suspect, but after I spotted the water flow into the expansion tank, I discarded it, however it could be intermittent, which I hadn't considered.

 

[Calps]

I didn't pay too much attention to it..........................

Inspection of the engine bay showed some coolant had gotten out...........................

Did you ever check the coolant level in the expansion tank?
Is it possible there was a small leak, maybe due to seals drying out, and that has caused an airlock due to low coolant level?

There was some coolant missing after the initial overheating (well I say missing, I know exactly where it went), however I refilled it, and not noticed any drop since (although I haven't recreated the overheating conditions to see if it starts spouting out any more).

This is making think it wasn't a "proper" leak so to speak, moreso something brought about when things are hot/overheating/under pressure.

Similar to my reply above though, I also bought an expansion tank, so fitting it should rule out leaky seals.

 

[Smartbear]

It sounds like the pump, particularly with the hot air disappearing from the heater. have you scanned the car for codes?
“Implausible pump speed” is typical for a failing pump, coolant over the engine bay is probably where it’s overheated & blown coolant out.
If you have a replacement pump waiting I’d fit it before driving the car again, avoid overheating the engine again as it can cause expensive damage - how many miles has the car covered?
Rob

 

[Mr Tidy]

I reckon Rob is right, and as you've got a new one anyway I'd be inclined to change it.

As it's electrical an intermittent fault seems plausible, especially as the car had been sitting for a while.

The pump on my first Z4 died instantly at 60K miles at 9pm in December on an unlit NSL dual-carriageway - no way was I stopping on that! So if it is of any reassurance I discovered it will go into limp mode to prevent any damage. :roll:

Thankfully when the pump died on my E91 325i at 135K miles it was 2pm on a sunny May day a few hundred yards from a layby, so I just waited for the RAC to tow it to my Indy.

 

[Calps]

The pump on my first Z4 died instantly at 60K miles at 9pm in December on an unlit NSL dual-carriageway - no way was I stopping on that! So if it is of any reassurance I discovered it will go into limp mode to prevent any damage

This is good to hear. While it didn't let it stay in the red for long, I had no reference point for it's tolerance - 10 seconds? 1 minute? 1km? 5km? etc. So that has given me some peace of mind at least.

My intention all along was to fit the pump and expansion tank myself, but circumstances have changed since creating this post, so I've booked it in to a local garage to have them do the work and give it a full health check at the same time.

With any luck, it'll be ready to grace the local twisty mountain roads come April.

 

[Mr Tidy]

This is good to hear. While it didn't let it stay in the red for long, I had no reference point for it's tolerance - 10 seconds? 1 minute? 1km? 5km? etc. So that has given me some peace of mind at least.

I must have driven about 5km with the red light on before it went into limp mode. I just kept to about 50mph to get some air flow but in 6th gear to keep the revs down.

I drove it to my Indy 4km away and from cold it didn't even reach Normal on the gauge if that helps.

 

[Calps]

It's probably good practice to update this to give some closure.... might be of use to someone down the line.

There was no great mystery to this, however it does appears that it was intermittent pump failure, rather than absolute pump failure.

The mechanic reported some loose/dodgy wiring to the pump, which was a contributory factor. He did note that after he mended the wiring, much to his disappointment, there was still some overheating, so the complete replacement of the pump was completed just to be safe.

Thermostat, expansion tank, and water pump replaced, a new coil pack, and some shiny new platinum spark plugs, and I was back in business, just in time to make my NCT appointment, where I failed on worn wishbone bushes, and the trifecta of lights associated with the YAW sensor :roll:

Well, at least the heating works again.....