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Discussion Starter · #1 ·
2005 MGTF 135

Fan will come on shortly after starting and stays on. This is with the engine cover off and boot open.
Temperature display is mid range eventually - radiator fan still idle.


I think there is a fault. Following the wires from the fan goes straight rearwards and into the wiring loom.
There is no sensor above the expansion tank.

What should I do to determine where the fault lies and how can I fix it?

Help appreciated

JR
 

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Starlight Silver MG TF 135
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I read somewhere that the way to TEST engine bay fan function is to (briefly) disconnect the sensor from it's wiring. I did this shortly after buying my 2002 TF135, and sure enough, the engine-bay fan started-up. Logic tells me (though I may be wrong) that the electronics controlling this system require a CLOSED circuit, or a resistance below a certain level, to keep the fan OFF. If yours is on all the time, this implies either a faulty sensor, OR broken wiring. Suggest you find a fellow TF owner who is prepared to lend you his sensor, plug it into your connector and see if your E.B. fan comes on. I think the sensor is at the top right corner of the picture below,
Hood Grille Sky Motor vehicle Automotive exterior

sorry do not have better pic, but message me tomorrow if you need a better picture
 

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As you say there is no engine by temperature sensor in later TF's. I understand that the ECU works out approximate temperature based on the engine coolant temperature. It is possible that the ECU coolant temperature sensor is faulty.
 

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MG TF 135
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Your engine bay fan is controlled by ECU, and measures the engine temp from the ECU Temp sensor (brown or black) , the temp gauge gets its signal from another temp sensor (blue) next to it.
You may have a faulty sensor over reading engine temp, a wiring problem maybe high resistance, or a problem in the MEMS3 ECU. I had constant engine bay fan after a remap. Check error codes and if you have a "Checksum" error it may be the ECU

I would check the temp sensor first if the engine cover is off. Its top back left of engine looking from the back of car, just back from the air filter.
 

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Discussion Starter · #5 ·
Thanks all. I’ll check this morning.
There is a hole fora sensor but no sensor above the expansion tank.
Looks like Chris is favourite so I’ll check later.
Thanks chaps.
 

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Discussion Starter · #6 ·
OK. Are both the sensors mentioned bolted into the same water outlet elbow - if so that's fine.
Can one confirm the correct replacement via Rimmers site - Coolant Temperature Sensor - MEK000030?
Thanks again chaps
 

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MG TF
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Yes MEK000030 is the ECU coolant sensor, as it is an engine part also try MEK000030L as this maybe cheaper (or more expensive) but it will be the same OEM part but will arrive in a Land Rover bag.
 

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Discussion Starter · #9 ·
Not fixed. 2005 MG TF 135
So I've replaced the HG and the black Temp Sensor.
Ran the engine up to temp, Engine Fan came on, Heater warm, Radiator cold, one feed pipe warm/ return cold.
So it appears cooling water not circulating.

When head had been removed found a chunk of what I thought was excess gasket goo in the same cylinder jacket where the HG had failed (bubbles in the water header tank). Might have been a bit of rubber hose???

MGF Center cambelt service 5K miles ago when the water pump should have been replaced. So I didn't this time!

Do thermostats fail closed? What suggestions to check before replacing anything.

Thanks in advance
 

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Being an 05 car it should have a PRT remote thermostat, not sure how they fail but they don't seem as reliable as the older type.

Another possibility is that someone has put a conventional stat in and two are fighting themselves.
 

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Discussion Starter · #11 ·
PRT is present. It's 5K miles since MGF Centre work so unlikely an extra thermostat - but I'll check.

Anyone else experienced PRT failure? And the consequences!
 

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mg_tf
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PRT is present. It's 5K miles since MGF Centre work so unlikely an extra thermostat - but I'll check.

Anyone else experienced PRT failure? And the consequences!
While doing a cambelt/ waterpump change I discovered that my '04 TF 160 had both a PRT and a 'conventional' stat installed.
After some investigation I deduced that the 'conventional' stat had been fitted when some head gasket work was carried out for the previous owner, the mechanic not realising (or recognising) that a PRT was already installed.
If you can beg or borrow one of those illuminated boroscope probe thingy's , you can disconnect the larger coolant pipe that attatches to the steel coolant rail - push the probe down into the steel pipe and you should be able to see on the screen whether a thermostat is fitted. It saves a lot of blood and pain removing the coolant rail and 'stat housing before you have to, if you see what I mean!
Best of luck ....B.
 

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Discussion Starter · #14 ·
Well since the last post l've replaced the PRT, checked the water pump, flushed water through all the courses without determining any cause - so back to square one.

I've asked the local MG expert to check the block and head.
Whilst I checked as best I could for true and in limits for both those items I can only conclude that he will recommend a head skim - but we'll see.

I still don't understand why the engine bay fan would operate prior to the PRT opening - especially with the engine cover off and boot open????
 

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'06 MG ZR +120 (HQM) '04 MG ZR 105 (IAB)
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If the coolant isn't circulating, I would say the most likely cause would be an air lock - very common on the K series if it is not filled and bled carefully, and especially so on the F and TF due to the greater distance to the rad. If the cylinder head gasket has just been replaced, I would think it unlikely that the head is to blame, and if exhaust gases were getting past the fire rings into the coolant, there would be significant residual pressure in the system when the engine has gone cold (a brief but noticable hiss when releasing the expansion tank cap).


Regarding the engine bay fan issue: has your car had a remap by KMaps by any chance? Several people have mentioned in the past that their engine bay fan runs constantly after having a KMaps remap. Most seem to have cured the issue by changing to a SAWS Tuning remap.

I would suggest that the engine bay fan running all the time is merely annoying, and won't do any harm, and is not likely to result in the engine running below its normal operating temperature if the thermostat and coolant temperature sensor are working correctly.
 

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Discussion Starter · #16 ·
Thanks for that. Car is new to me and was told it had a remap - see if I can find out.
Well I do take care bleeding but maybe
It could be the engine hasn’t been hot enough to open the thermostat - after HG replaced etc etc. I was certainly confused with the engine bay issue but I’m sure the HG replaced still allowed gas into the waterworks.
We’ll see what the man says safty .
Thanks again
 
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