Cooling issue

[Rockettvr]

Morning friends
I'm currently experiencing cooling issues with my 350i
A bit if back history first: A while back I blew a head gasket - a hose went and by the time I realised I had well and truly cooked it. Anyway head gaskets replaced I had a run out to a car show (around 120 mile round trip) with no apparent issues.
Just before the fest I drained the cooling system and replaced the coolant with a new 50\50 mix of water and antifreeze
On the way to the fest a problem became apparent with the cooling
The temp will hold steady around 90 (pre head gasket Change it was more like 80) for long periods then it will drop to about 80 (takes 2-3 seconds) it will then stay there for a random period of time (a few secs to a mins) then rapidly rise to just under the red 98 degrees ish where it will stay for a random amount of time (a few secs to a few mins) before quickly falling to settle at 90 before repeating the process again.
It seems to be more prevalent at motorway speeds less so at 30
I lost around a pint of water on the run (140miles roung trip)and on a run this morning its apparent its blowing the water out of the expansion tank cap

I've tried several times to burp the system
So what do you think
1 Just a stubborn air lock
2 faulty thermostat
3 faulty expansion tank cap
4 head gasket failed
5 something else ??
As always your help is appreciated
Cheers Ron
Eta
It doesn't actually boil over
The fans work as the should

Edited by Rockettvr on Sunday 17th July 12:15

[Rockettvr]

Number 7 said:

Ron, that header tank is not the usual type, and there doesn't seem to be any auxiliary catch tank. Has the cooling system been modified? Is the tank cap of the correct rating (15 psi IIRC)?

Hi Paul
I was aware that my cooling system differs from other wedges Tha id seen but thought that I was a TVR thing that they'd changed something according to what the had to hand or a cheaper alternative
Its always been reliable till now - I put a 82 degree stat in soon after I got the car and its always run slightly cool (80-85 deg)
The cap on the expansion tank is a motorcraft an on a bit of investigation looks to be a mondeo item. The cap is rated at 21 psi
As for expansion the coolant level just rises and falls inside the resevoir - usually sits on the min level when cold on the max level when up to temp
After the last couple of outings its expelled around a pint of water so once cooled down again the reservoir Is nearly empty
The way the temp goes up and down in cycles makes me think it is just a stubborn airlock going round the system
I'm hoping its not the head gasket again - surely if it was the head gasket it would just blow all the water out and boil ???
I'll try another burping session as you suggested Paul and hope for the best before delving deeper
Cheers Ron

[Rockettvr]

Hi all
Not had a chance to burp the cooling system yet but in response to some if your questions
Head gaskets were composite elring I think (came from Island 4x4)
Used new stretch bolts torqued in the correct sequence and to correct torque levels
Outer row of bolts were left out
Hoping to get to burping system tonight -
I shall report back

[Rockettvr]

Hi all
I think I may have stumbled upon the cause of my fluctuating temperature issues
This morning I burped the cooling system as per number 7 instructions
All seemed well - didn't seem to get any air out but the car ran up to temp , the fans cut in at around 90 and temp came down again - cool - fixed it - time for a test drive. A quick run out and the temperature quickly rose and rose and rose bks pull over to let it cool quietly swearing under my breath and I realise theres something missing - the sound of the fan running. So it would appear I've got a temperamental fan
I'm guessing its more a faulty otter switch rather than the fan itself so will wire in an override switch as a temporary measure
Id like to replace the otter switch with an adjustable control - any recommendations??
There's one in Car builders solution website which seems to be ideal - the temperature probe goes in the top hose http://www.carbuildersolutions.com/uk/adjustable-f...
Thanks all Ron

[Rockettvr]

Hi all
Thanks for the offer of the bits zig but I'm sorted. New adjustable stat ordered
Will have a tinker tonight to get everything prepared and check its not a fan issue rather than the otter switch
Not going to replace the otter switch as
A access is crap
B dont want to disturb it and risk inducing a leak
C want some adjustability to fine tune it
Will report back once I'm up and running again

[Rockettvr]

Evening all
Well my woes continue
New adjustable fan stat arrived and fitted. All seemed well set it to 40 deg ran engine up and fan kicked in set to 50 deg and after a few moments fan kicked in again, reset to 85deg (82deg thermostat fitted) and time for a run. Unfortunately the temp rose and rose so pulled over to let it cool- fan was running but cut out quite quickly even though gauge was showing 95 deg??
Then whole sitting waiting for the engine to cool- bang-the temp gauge went off the scale as if id flicked a switch
Even turning off the ignition or pulling off the connector to the sender didn't affect it - after a couple of mins I turned the ignition on and off and it immediately dropped to 90 degrees ???
All a bit odd
Onwards and upwards
The engines still overheating
Not sure if I can trust the temp gauge
Not sure if the new fan stat is working correctly or accurate
Possibly got 2 different temps going on - one temp at top hose (where fan stat is) and another at the engine itself (possibly a stuck /faulty engine Stat ??)
Next plan of attack
Might remove/replace engine stat to remove it from equation
Borrow my company's laser thermometer so I can get an accurate measurement of the engine/top hose /radiator temperatures
Next episode to follow shortly.....
Ron

[Rockettvr]

mrzigazaga said:

Hi Ron.

Where did you place the thermo switch/Probe?...

It also sounds like you have a dodgy gauge or sender.

Hi zig
Probe is in top hose as recommended on the instructions that came with it.
My current train of thought is that the engine stat is faulty and not opening therefore not getting water flowing through the rad and overheating. This would also explain the reluctance of the fan to operate correctly as until the engine stat opens the probe in the top hose wont be getting the hot engine coolant flowing over it. Not sure if my hypothesis is correct but its the only ine I've got at the moment !!

[Rockettvr]

Jack Valiant said:

Yep sounds like stat ..... I would drain the coolant take the stat out remove top and bottom hoses on the rad run your pressure washer through it and see if any sludge come out allow to drain. Check stat is working using a kettle when her who must be obeyed is not looking! Replace stat or leave it out if you do not mind a bit more fuel on cold start

Re-burp the car and test

Chris

Cheers Chris
Was my plan of action next
Going to borrow a laser thermometer to accurately measure all my temps to see how accurate my temp gauge and adjustable fan stat is also.

[Rockettvr]

adam quantrill said:

A good test of the stat before removing is to run the engine on fast idle from cold and feel the top hose, it should be cold for quite a while then suddenly get hot.

Hi Adam
On the way to the fest the temp would rise and fall, now it overheats. Wether it was the stat being temperamental and has now failed altogether I'm not sure. Yesterday when I overheated the top hose was hot but wether 80deg hot ie fan nit kicking in or 100 deg hot ie fan control not calibrated properly I'm not Sure
Basically I've no confidence in any if the cooling system components until I can accurately measure the temperatures in the system to see how accurate everything is and that they're working correctly
Think ill pull the stat - if its being temperamental even testin may not show a fault but if I dont have one fitted it cant be a factor
A rad flush and refill, followed by running the engine up to temp monitoring everything and checking with a laser thermometer should tell me a bit more about what's happening
Cheers Ron

[Rockettvr]

Hi all
Martin - think you're right about gauge - seems to be an electrical issue once the engine gets very hot - a bit of a red herring
As for drawing air in via heater tubes - how quickly did this happen ? At the moment mine will over heat on a very short journey 8 miles ish - going from cold it will just get hotter and hotter until I have to pull over to let it cool

Adam - I've not discounted the head gaskets being the culprit - they were the last thing I fiddled with after all - but its odd that the engine is on the point of boiling but the fan doesn't operate until I turn the adjuster down to 75-80 degrees
Not noticed any bubbles in the coolant.
Picking up.the laser thermometer today so hope to pull stat ,flush rad and measure all the temperatures tonight
Thanks for all the advice

Ron

[Rockettvr]

Hi all
Not counting my chickens yet but I think I've sorted it
Wasn't able to pick up the laser thermometer today but thought id strip out the engine stat and test it - after all its only a 5 minute job.... And that's all it was for a change 5 mins later I had the stat in a boiling pan of water on top of the cooker (yes the wife's out) and nothing -its not even attempting to open.
Flushed the rad and put the car back together without a stat fitted and ran it up - all seemed well so nipped out for a run and its running super cool - around 60 degrees while moving and even after idling on the drive for 10 min it had only hit 70.
Not lost any coolant and its not getting super-pressurized like before ,no bubbles in coolant
My cooling system is different from a standard 350i and I'm wondering if that's why it was blowing coolant out when it overheated - there's just not enough expansion room in the coolant reservoir at high temperatures??
The new adjustable fan stat I fitted isn't very accurate - temp gauge was showing 60 degrees which is probably about right as I could comfortably rest my hand on the top hose but the fan was running until I adjusted it to above 75 degrees . Will have to get the laser thermometer out to get it set up properly once I fit a new engine stat.
The fluctuations in the gauge on the run up to the fest was probably the stat on its way out and slowly failing until it gave up the ghost last week and just started overheating every time.
I'll order a new stat (88 degree like the one that came out) and report back to confirm all is well
Once again guys thanks for your input - it cant be easy trying to diagnose a problem from my appallingly poor descriptions of the symptoms
Thanks all
Ron

[Rockettvr]

Thanks for the link Paul - was struggling to find a wahler stat - but I've ordered a OE 82 degree stat from Grimmers
Ta Ron

[Rockettvr]

Hi all
Normal service is resumed.
New 82 degree stat with jiggle pin received and fitted.
Been out for a run and its back to normal, temperature hovering around the mid 80s degree mark
On sitting on the drive all seems to work well, temp rises to 88degrees, stat opens, fan kicks in and temp falls to 82 degrees,stat closes, temp rises to 88 degrees etc etc
Thanks for all the advice and support
Ron