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hi guys,

Are the temp gauges calibrated the same between the two variants or will an early cluster read low in a thor car?

I bought a thor 4.6 with the heads off. have it running and driving now, but the temp gauge reaches only about a quarter of the way up. I cross checked with a cluster from a wreck (early) and it read the same. sadly i didn't know about the cluster/becm odo error thing at the time, but that's another story.

I had it hooked up to diagnostics and it showed it was idling away at about 90C, so i know the gauge is wrong (and one half of the sender is OK), but its pointless replacing the sender if the gauges are different.
 

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1995-2002 Range Rover P38A
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My Thor only reads 1/4 , I changed sensors with no difference. I’m sure someone with more knowledge will chip in, in my eyes I can’t see why a gems or Thor would read different, BUT it is a p38, so nothing would surprise me.
 

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heads are mostly universal across late Classics, Disco IIs and all p38s... except for the addition of SAI. temp sesnsors are the same save for Bosch WITH SAI, because the sensor is in the bottom of the radiator instead of in the intake. Due to the buffering space in ECU programming the temp gauges are NOT accurate. You have a wide range of temps hidden once the engine temp rises to the basic gauge level. Both GEMS and Bosch rather suck because it is designed for idiots instead of being factual.
 

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1995-2002 Range Rover P38A
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Your thermostat is probably stuck open there is no reason why the temp should not be in the middle . These RR have serious cooling systems.
Good Luck
 

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1995-2002 Range Rover P38A
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Don't forget that the temperature data comes from thermistors, 2 in one single sender unit on the Thor. One feeds to the BECM, gets digitally crunched and then on to the gauge, the other feeds the engine ECU and is where your diagnostics kit will be pulling the temperature information from.
Thermistors are resistance based (!) so any extra resistance in the circuit (corroded connectors, frayed wires etc) will "bias" the ultimate reading. Check your wiring and connectors between the sender and the BECM.

coolant curve.JPG
 

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If you take the cluster out, break the seals and look along the top of the circuit board on the back, you will see 3 trimmer potentiometers marked VR1, VR4 and VR3. These are for calibrating the readings on the gauges. VR3 and 4 adjust the speedo with VR3 dealing with Slop Angle and VR4 dealing with Offset while VR1 is for the temp gauge. If you are sure that the sender is good and giving the correct resistance for temperature, you can adjust VR1 to make the gauge sit in the centre of the scale. There are similar trimmers on the other side of the board that deal with the rev counter and fuel gauge. Don't forget that the fuel and temperature gauges are heavily damped so you need to adjust the trimmer and wait for the gauge to move, they don't move instantly.
 

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thanks everyone for the responses. i realise the gauges are an "average" rather than accurate, but as the car is so new to me, and came to me in such an unknown state, the gauge reading a quarter makes me particularly uncomfortable.

at purchase, one head was off because of an external compression blow under the exhaust manifold. liners all looked level etc. pistons looked the same colour etc. during the incident it apparently blew coolant out, but the cap was visibly broken and the fellow who pulled the head claimed a few of the bolts were loose. i purchased it and took the other head off and sent them off to be checked, then reinstalled them with studs and new cam/lifters. once running, it was really rather rough sometimes, put pulled smoothly like a train at other times, putting my old GEMS car to shame. i replaced the AFM and things mostly settled down. it starts smoothly on petrol but runs lean, i think when you take off. when it gets to a certain temp it switches to LPG and runs flawlessly.

it was on the first happy run that the heater matrix suffered a catastrophic failure. this has made me paranoid about cooling system pressurisation (cracked block). once the matrix was bypassed, i noticed the top hose was hot, and the bottom was cold, so i replaced the thermostat. things remained the same in workshop conditions, but after driving, the bottom heats up as well as one would expect.

the top hose firms up a little more than you'd expect, but the tank never blows coolant out, gauge is steady in traffic with ac on a 35C day, etc (but obviously the gauge isn't working correctly).

from cold it'll idle with the cap off happily, but as the top hose heats up, the header tank bubbles and overflows.

from hot one can remove the cap when not running and there is only a normal amount of pressure release.

after it is parked overnight the pressure dissipates as you would expect.

the overflowing header tank when top hose is hot (bottom one cold, haven't tried after thermostat has opened) and the cap off concerns me, but with the cap on it seems fine, doesn't use water, etc - other than the heater core incident.

anyway the first step needs to be a relatively functional temp gauge. the car is a very early update, but the cluster is definitely from an early car by appearance and also date stamp.
 
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