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Old 10th-February-2009, 16:16
Junior Member
Join Date: Mar 2007
Posts: 6
Default Thermo Time Switch in V8 engine

Advice sought.........

1986 Petrol Manual Range Rover Classic. Last week it wouldn't start (typical, just when the snow arrived)

At the weekend I towed it, and it started almost immediately. Drove it about 20 miles, stopping a few times, and it behaved fine. On Monday, with floods forecast, it wouldn't start again. It tried a couple of times - then nothing

I've fished around, it has petrol, spark etc. so I started thinking about cold start problems and went for the Coolant Temp Sensor in the head. Measured resistance of 47 Ohms, whereas an article I found on web suggested it should be about 4.7K at 0 deg. C, reducing to about 150 Deg C at boiling.

Brought culprit into work today and inspected closely with magnifying glass, and it says:-


5 89 (I'm guessing the date of manufacture)
12V 40W
35Deg. C 8 Sec
A search on the top number identifies it as a "Bosch Thermo Switch", fitted to a Ferrari 308GTB, Mondial, Jag XJ6 or Peugeot 505 - but not to a Range Rover.

As it is younger than the engine, so someone has fitted it at some time in the past. It was located in the front of the head where I think from the handbook the temp sensor should be.

My question is.... does anyone recognise the part, is it an appropriate replacement - or is it completely wrong and the poor old thing has been starting in the absence of any correct engine temp data. I will say it has always been a slightly reluctant starter, esp. when its cold out.

Any observations gratefully received

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Old 10th-February-2009, 16:44
Irishrover's Avatar
Senior Member
Join Date: Jul 2007
Location: Aberdaron, Gwynedd, North Wales
Posts: 5,024
Default Re: Thermo Time Switch in V8 engine

The temperature sender (Not for the gauge) is listed as a Cold Start Sensor
Part no. ETC 8496 cost around £12. The sealing washer is Part no. 243967
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Old 12th-February-2009, 13:37
Junior Member
Join Date: Mar 2007
Posts: 6
Default Re: Thermo Time Switch in V8 engine

I have some further information, in the hope that someone may be able to assist:-

The part I’m looking at is called a “Thermotime Switch”, its not the Temp. Sensor for the gauge, and fits vertically into the head. The part number I have identifed for it is EAC 1385. (tho’ the one I have is a Bosch part – listed as fitting a Ferrari Mondial)

Marshalls in Cambridge claim it is obsolete, but I have found one with a Land Rover specialist. The bad news is that it is £60, so before I buy it I’d like to know I need it.

The one I have has a resistance of approx. 46 Ohms at room temperature, which does seem odd for a “Switch”. Can anyone tell me if that is normal, and what the function of it is?

The sympoms are that the old thing won’t start. If I tow it it starts almost immediately, and then runs, starts and stops fine for the rest of the day. Wait until next day and the situation is the same. That says to me its not ignition (spark is good), or elements of fuel injection such as pump, ECU etc. It appears to be temp dependent, which is why I’m suspicious of this switch as I believe its purpose is to relay engine temp to the ECU.

Can anyone comment???

Thanks in anticipation
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Old 12th-February-2009, 14:32
al-one-arm's Avatar
Senior Member
Join Date: Jul 2008
Location: burnham-on-sea,somerset
Posts: 248
Default Re: Thermo Time Switch in V8 engine

coolant temperature sender figures:
coolant temp resistance(ohms)
-10c 9200
0c 5900
+20c 2500
+40c 1180
+60c 600
+80c 330
also measure the resistance between each sensor terminal and the body of the sensor, an infinity(open circuit)reading should result. if the sensor fails any of the tests renew it.

air temperature sensor

same readings as above should be present(obviously cannot get to the high temps)

thermotime switch:
check the rated temp stamped on its body
disconnect the battery earth lead and unplug the thermotime switch connector.
measure the resistance between switch terminal w and earth, if the coolant is hotter than the switch rating an infinity(open circuit) should be recorded, if cooler than rating a zero or very low resistance(closed circuit) should be recorded.renew if fails.
if above test is satisfactory, wait until coolant is below rating then
connect a switched 12v supply to terminal g and earth, leave the ohmmeter conncted to terminal w and earth, switch on the 12v supply and record the time taken for the switch to change from low to high resistance, the time taken will depend on the coolant temperature as follows:
coolant temp delay time
-10c 8 secs
0c 4.5 secs
+10c 3.5 secs
+35c 0 sec
renew the switch if the recorded time differs widely from above
just another couple of thoughts.
a seperate cold start injector supplies extra fuel for cold starting enrichment when engine is cranking,
extra air valve. check that when the engine is being cranked on the starter motor that battery voltage is present at the extra air valve, air valve resistance should be 33 ohms
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Old 12th-February-2009, 15:29
Irishrover's Avatar
Senior Member
Join Date: Jul 2007
Location: Aberdaron, Gwynedd, North Wales
Posts: 5,024
Default Re: Thermo Time Switch in V8 engine

The part no. quoted is for the ECU-Not the gauge sender.
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