4200 Fans running, hot start issue

atreyu1

Member
Messages
183
First time this has happened.....

I noticed tonight the fans were running when I fired the car up, I didn't think anything of it. I noticed the water temp didn't get above 50*c on the gauge on a 7/8mile run. Then noticed the fans were running when I got to my destination.

About 15mins later I attempted to start the car to come home, but it just cranked over rather fast but didn't fire at all. (I think the fans were running)

I tried again and gave the throttle a press, like you would do in a carburettor car and it fired up and then ran ok, apart from the fan issue.

How I've read on here it can be a number of things but does anyone have any suggestions on which to go for first?

I've read it could be a sticking thermostat (guess this can happen at anytime), causing the car to go into a "safe mode"

Also read it could be a coolant temp sensor?

Fan resistor near the radiator, although I've not been anywhere near it so I doubt its that?
 

allandwf

Member
Messages
10,958
I had a volvo where the MAF was faulty, and the fan ran continuously. ( The plug had actually come adrift.)
 

GeoffCapes

Member
Messages
14,000
Sounds like what I had on mine. That was an air temp sensor.

An Italian tune up 'fixed' and never happened again. And I never fitted the sensor.
Which was handy as my hands and arms were too big to fit into the gap to fit it.

If you're coming to Brooklands on Saturday you can have my sensor as obviously I don't need it now.
 

j s pollo

Member
Messages
162
Hi I have the same problem which is being looked into by Migliore of Bromsgrove I have had this problem 18 months even they dont know whats causing it what I do when the problem crops up as a tempory fix to get your motor running again I remove the battery leads and tap them together for about 20 seconds this clears the errors and remove any charge in the system all will go back to normal.

Please note this is only a tempory fix the problem may go away if your lucky but thats italian electronics for you.This is a common problem with the 4.2 and no one seems to know what is causing it if you find out let us all know ..
 

conaero

Forum Owner
Messages
34,593
Turn the AC off first to see if the fault goes away by illuminating the ECON button/AC off.

This will rule out an AC and point to the issue above.
 

DPS20K

Junior Member
Messages
168
As per my other post on this subject, I had a similar problem with my GS. Had to do a battery reset to get it to start every time it happened. It only happened on cold days, below 4 degrees. Emblem diagnosed it as a faulty thermostat and changed it. The problem hasn't happened since.
 

atreyu1

Member
Messages
183
Geoff, I'm not at Brooklands unfortunately, which and where is this air sensor located?

I'll make sure the aircon is OFF and report back

I did wonder about the thermostat but it just seems odd that'd bring the fans on, Am I correct in saying that the thermostat comes with the complete alloy casting? (Making a cheap part costly!)
 

DPS20K

Junior Member
Messages
168
Myles at Emblem suggested that if the thermostat failed the engine sees unexpected temperature and goes into a safe mode, with fans running full on and the exhaust valves open on a GS. Doesn't explain why it won't start but it did fix the problem on mine when they replaced the thermostat. I think it does come with the casting.
 

GeoffCapes

Member
Messages
14,000
Geoff, I'm not at Brooklands unfortunately, which and where is this air sensor located?

I'll make sure the aircon is OFF and report back

I did wonder about the thermostat but it just seems odd that'd bring the fans on, Am I correct in saying that the thermostat comes with the complete alloy casting? (Making a cheap part costly!)

It's on the side of the engine block. Drivers side front wheel off, wheel arch liner out. Using an skinny arm with 4 elbows in it, squeeze through a gap the diameter of a toiler roll and then get the sensor out, in zero room.
Left me with a bruised arm just attempting it. There's a thread on here somewhere!
 

spn

Junior Member
Messages
88
My TCU occasionally logs a temperature fault (can't remember the code). This doesn't bring up a CEL but appears to put the car into some kind of safe mode where it runs the fans and also makes the gear change / clutch engagement slower.

Clearing the fault sorts the issue.

I think it's either the temperature sensor or maybe the thermostat, have both but haven't fitted either - will get around to it at some point. Only seems to be an issue when it's cold.

Cheers,

Simon
 

Caldy999

Junior Member
Messages
445
Have someone check the fan resistor - just had similar issue which was fixed by a Phil at PKSupercars.
 

j s pollo

Member
Messages
162
Hi.
As I mentioned earlier over the last 18 months I would have the same problem cropping up the last time it happened the lads at Migliore had just serviced the motor and must have upset something so I went thro the process of resetting the electronics as I have described earlier but I was doing the reset when the engine was hot thermostats and sensors still warm.
Well that got me thinking I have replaced just about everything under the bonnet time to try something different I done a cold reset got up early one morning engine cold sensors thermostats etc all cold disconected battery leads tapped them together cleared everything reconnected leads and upto now the problem has ceased and for the last 3 weeks the electronics are behaving themselves
This reset only takes a couple of minutes give it a try before going thro the expense that I did might save you a few head aches.

If it does not solve the problem as the Independents and the lads on this forum will tell you nine times out of ten its usually the Resistor at the bottom of the radiator But try the cold reset so far its worked for me Touch wood

Best of luck....
 

j s pollo

Member
Messages
162
Well its November now Five months since I done the reset as described above and my problem has not returned keeping my fingers crossed
 

doodlebug

Member
Messages
913
Intermittent temperature problem

Déjà vu.

I had exactly the same problem as the OP, except mine was annoyingly intermittent. Often the car would start from cold with the engine fan(s) running, even when the exterior temperature was below zero. The temperature gauge appeared to be working correctly. The car could be impossible to start when it was warm even after a gentle run. The engine would crank rapidly and the car would reek of petrol but it wouldn't catch for around 5 minutes. A tad embarrassing at petrol stations. It didn't affect normal driving except for maybe the fuel consumption, but I don't take a lot of notice of that.

The first time it happened, around 5 years ago, the RAC diagnosed that there was a faulty engine temperature sensor using their expensive bit of diagnosis kit. They took the car to Grimaldi's but had helpfully cleared the fault code so Roberto couldn't find anything wrong. He suggested it may be one of the MAF sensors but without the problem being present when he had the car, he couldn't really diagnose the problem.

The next time it broke down, I took advantage of Lancaster's free pick-up and drop-off service to get a second pair of eyes to look at the problem.

'They all do that Sir" they said. After throwing my toys about a bit they agreed to replace the temperature sensor after running the diagnosis and seeing a failed engine temperature sensor.

The car seemed OK for a few weeks until the fault subsequently reappeared. Back to Lancaster's and they diagnosed the replacement sensor was also faulty. No surprise there - the Italians invented electricity but I've never been sure they have mastered it. So they replaced the sensor.

Fast forward a few weeks until the fault reappears ...

It was getting a bit boring now so Lancaster's suggested it may be a problem with the wiring loom at which point I thought, "Oh bother - I'll just put up with it and plan my refuelling trips more carefully in the future".

To cut an already tedious story short, I took the car to Grimaldi's for its annual service and Roberto had a couple of attempts to diagnose the problem and suggested it was probably the ECU. This went down like a pork chop at a... So I continued to put up with it. I actually went to the trouble of resoldering all of the accessible joints in the ECU which bizarrely seemed to fix the problem for the longest period of time so far, around about a month.

However, during this latest cold spell, I noticed the temperature gauge wasn't moving as it usually did. I suggested to Roberto that it may be the radiator thermostat as per the advice on this forum. He replaced the said part but the fault was still present so he tried replacing the gauge controller. Weirdly, this controls the engine fan and monitors the engine temperature. So far, the problem are sorted. As a bonus, the dash lights are no longer intermittent but I put that down to Roberto disturbing the relevant connections. Certainly the car is back to its glorious former self and is a really fantastic drive again.

Top marks to this forum and to Grimaldi. I am hopeful this time that the problem has permanently gone, but I will keep you updated if it comes back. It certainly feels better than it has in a while.
 

Gp79

Member
Messages
1,393
Good info, i had it happen once so keen to know the correct fix.

I have actually ordered a new temp sensor / thermostat and replaced the fan control resistor a couple of years ago (fans only ran on high speed instead of ramping up correctly)and the fan resistor fixed that issue.

What or where is the gauge controller? As you already replaced the engine temperature sensor.

you mean on the back of the odometer? that operates the temp needle?

Thanks Greg
 

doodlebug

Member
Messages
913
Hey Greg

The fan resistor was replaced about 5 years ago for the same fault you described, coincidentally about the same time as the hot-starting fault started happening. I'm not sure if the faults were related though.

I asked Grimaldi to replace the thermostat because the gauge did not register the engine temperature and the heater seemed to take ages to warm up. This didn't fix it so Roberto replaced the gauge controller which I think is under the dash but I'm not exactly sure where. It communicates with the main ECU over CAN and drives all of the gauges so it should be easy to trace.
 

Gp79

Member
Messages
1,393
Thanks for the reply, i'll have a look for that module and swap it out if the hot start problem happens again...