High water temp but no heat from heater

[andmas]

Hi,

Hope someone can help with my problem.
A couple of days ago the temperature gauge on my 2007 Z4 3.0Si went into the red and the red warning light came on (this was after normal driving for about 8 miles from cold). I stopped to let the temperature reduce and noticed that the fan was on. I carried on home and again after about 3 miles the temp had gone up again and the red light came back on. I let the engine cool right down and opened the rad cap and found that the coolant was to the max (float stick protruding above the opening).
Today I used the car and after about 10 miles the temperature had gone above the normal mid point but not high enough for the red warning light to come on.
I've also noticed that the heater only puts out luke warm air and that is when the temp control is turned up to max.
Could the problem be the thermostat and if so how easy are they to replace? The car has done 35,000 miles so I hope it isn't the water pump, which I understand can be a problem on higher mileage cars?

Thanks in advance for any help

 

[Stuart Truman]

If you've not lost coolant, it could be the thermostat sticking. Sorry but I can't help on its location, never changed one on a modern engine. If you can get at it, you can test it by putting it in a pan of water and heating it. You'll see it open (or not if it's jaffed)

 

[andmas]

If you've not lost coolant, it could be the thermostat sticking. Sorry but I can't help on its location, never changed one on a modern engine. If you can get at it, you can test it by putting it in a pan of water and heating it. You'll see it open (or not if it's jaffed)

Yes I thought it could be the thermostat sticking but wouldn't that make the air from the heater in the car hot (as the the engine coolant temperature) not just luke warm?

 

[TO//M]

If you've not lost coolant, it could be the thermostat sticking. Sorry but I can't help on its location, never changed one on a modern engine. If you can get at it, you can test it by putting it in a pan of water and heating it. You'll see it open (or not if it's jaffed)

Yes I thought it could be the thermostat sticking but wouldn't that make the air from the heater in the car hot (as the the engine coolant temperature) not just luke warm?

No, the coolant in the block will not circulate through the heater if the thermostat is closed.

 

[Jembo]

Water pump failure / seizure?

 

[WLH]

Water pump failure / seizure?

That's what it sound like...

 

[bcworkz]

The N52 has an electronically controlled electric coolant pump. I don't think it even has a traditional thermostat, the DME turns the pump on and off based on ECT sensor values. You should get trouble codes if there's any problem with the pump. Sorry, I can't really point you in a more promising direction though.

EDIT: I just stumbled onto the N52 "thermostat", it looks more like an electrically controlled valve body, and it ain't cheap!

 

[andmas]

Thanks for all the replies - looks like water pump or "thermostat" - both sound expensive jobs to replace!

 

[srhutch]

The thermostat is also partially electronically controlled. Mine failed on my old 2.5si (N52), although the symptoms were the car wasn't getting warm.

My first thought would be thermostat stuck closed, after that water pump.

 

[andmas]

I spoke to my indy today and he thought that the most likely thing was a small leak, probably from one of the hoses and as the system cools air is being sucked in through the leak point . This is causing an air lock in the system - the expansion tank is showing as up to level due to the air pushing the coolant up.
There is some signs of coolant around the expansion tank cap and as I said in my first post the float is to the top (indicating that there is air pushing up the coolant).
I've also noticed some blue water (presumably coolant) under the car so before changing the "thermostat" or pump I'll remove the splash guard underneath and check all the hoses.

 

[moonshine]

i had a similar problem in my first ever car, a G reg 2.0l vauxhall Carlton in the late ,90s
it used to overheat, with cold air from the heater, then all of a sudden i would get hot air out of the vents & the car would run cool again.
I initially thought of the thermostat, so checked & changed it with no effect. I eventually settled on a blocked heater matrix, and it seemed to become less common once it had been flushed properly.
It was aso likely to have airlocks in the heater matrix which stopped water circulation. The header tank was full to the brim when the car was overheating, & it would return to normal when the car was running properly.

 

[andmas]

I've now removed the top panel and the bottom splash panel and checked the hoses - no sign of any leaks (although couldn't see all the hoses). To try and see if there was an airlock I also drained the coolant from the rad and expansion tank (not the cylinder block) - there was 5 litres. According to the hand book the total capacity is 7.6 litres but unsure how much would be in the cylinder block - does anyone know? The strange thing is I could only get 4.5 litres back in - had bleed screw removed and kept squeezing the top and bottom hoses to try and expel any air in the system. Anyway started the engine to run it up to temperature (actually went up to just before the red light on the gauge after about 10 minutes before I turned it off). For some reason the fan started at full speed just after the engine was started and the gauge still on the blue (I thought the fan should only be at full speed when the temperature was getting above normal?). When I turned the engine off and checked the top and bottom hoses the top hose was hot but the bottom hose cold. Also still no heat in the cabin.
So can anyone advise:
1) Why would the fan be at full speed when the gauge is still on the blue
2) Why was the top hose hot and bottom hose cold - does this indicate that the "thermostat" is not working - if so are there any fault codes that indicate a faulty "thermostat"? How easy is it to replace the thermostat? - I've been quoted £82 for supply of the complete housing and ali bolt.
3) Do the symptoms above also indicate water pump as suggested in previous posts?
Thanks for any help

 

[srhutch]

As I said before my thermostat was faulty, no error codes were given so don't think you will see anything. I would still bet the thermostat is stuck close so the coolant isn't circulating hence why the rad is staying cold as only the water around the block will heat up.

I wouldn't have thought it would be hard to replace. It might even be worth removing and seeing if it's possible to test in some hot water like you used to be able to do. Even if you can't see the stat in the housing if you pour cold water in one end it shouldn't come out the other. Dunk in some very hot water for a few minutes and then pour some water though again and it should come out the other end.

 

[alekos911]

I once had the same problem in my coupe. It was a cold winter night and while driving I got a awful beeeeeep and I saw the temperature rising to the red area and then almost instantly going back to normal. I had only covered six mile from cold. I instantly stop the car and put the heaterin max (with closed engine). Left it to cool down and when I fired it up again I notice no hot air. Everything else seemed to be ok. I left the car where it was and next day I got it towed to the stealer. He did run a test on the pump and it was malfunctioning. At the time my car had only covered 30000 kms. Because the pump is electric you don't get definite signs that it's gone.
So please check this. If it is the pump it would be an expensive fix.
Do not neglect this though, because our cars are prone to overheat damage due to their I6 engine configuration.

 

[bcworkz]

Hot top hose and cold bottom indicates inadequate coolant flow. But we already knew that. Could still be caused by either thermostat or pump.

I did find a thermostat reference for an M54 engine, it appears to be the same as N52. The electric control only activates during extreme heat conditions. For practical purposes, it works conventionally, but because of the sealed electric connection, you have to replace the entire housing. It is actually a 103 C thermostat, so if you want to test it on a stovetop, you'll need to heat it in coolant.

 

[andmas]

Thanks for the helpful posts.

I've now found the correct way to bleed the system (N52 engine with an electric pump). The procedure apparently is to turn the ignition on, set temp dial to max, fan on low setting then press accelerator right down for 10 seconds - the pump should then start and then run through its automatic 12-minute bleed cycle. When the pump starts it should be audible but when I did this procedure twice each time there was no sound from the pump. I fear that this is further proof that its the pump that failed.
I'm getting prices for the pump (been quoted £82 for the thermostat) and will also get estimate from indy that I use to do the replacement. Depending on indy's price I'll decide whether to replace myself or take the car to him (replacement of pump and thermostat 'looks' relatively straight forward assuming all the hoses come off ok but not sure if I fancy laying on my back in puddles of coolant!).

 

[alekos911]

Thermostats have a "fail safe" design, meaning that most of times they stuck open and not closed. The problem scrutch had with his cars thermostat proves that.

 

[andmas]

Update for anyone interested - it was the water pump as suggested by Jembo, WLH and alekos11. Seems to be a common problem with these electric pumps - I tried a number of main dealers and they all said the same "none in the country and none in Germany - could be 2 months before any come in" !!
In the end I managed to get a HEPU pump (German made) from euro car parts. Good to get back in the car
Thanks to all for the input.

 

[dmo]

Thanks for the helpful posts.

I've now found the correct way to bleed the system (N52 engine with an electric pump). The procedure apparently is to turn the ignition on, set temp dial to max, fan on low setting then press accelerator right down for 10 seconds - the pump should then start and then run through its automatic 12-minute bleed cycle. When the pump starts it should be audible but when I did this procedure twice each time there was no sound from the pump. I fear that this is further proof that its the pump that failed.
I'm getting prices for the pump (been quoted £82 for the thermostat) and will also get estimate from indy that I use to do the replacement. Depending on indy's price I'll decide whether to replace myself or take the car to him (replacement of pump and thermostat 'looks' relatively straight forward assuming all the hoses come off ok but not sure if I fancy laying on my back in puddles of coolant!).

When you say ignition on - do you mean you actually start the car?
When you say press accelerator right down for 10 sec - do you mean flooring it, all the way past kick down (mines auto), or do you rev it to a certain RPM? Surely you dont redline it for 10 sec...

 

[maxman]

You don't start the car,just turn the ignition on.