Testing actual water temp

Testing actual water temp

Author
Discussion

Paulprior

Original Poster:

864 posts

104 months

Wednesday 10th February 2016
quotequote all
Hi
I have recently bought a 95 Chimaera 500 and due to the weather I have only driven it a few times so far, but one thing I am cautious of is that as at standstill the temp gauge goes from its normal 90 up to 110 quite quickly, 3 or 4 sets of lights is enough, or if I just let it idle it's the same.
I have had a new standard otter switch fitted, the fans cut in at about 110 but only stay on for 1 or 2 minutes before switching off again, the gauge doesn't move in that time, I tried measuring the swirl pot temp with an IR gun but it wasn't happy pointing at shiny aluminium and recorded 150.
So I figure that either my display or sensor could be reading high and the point when the fans switch on is actually around 90 instead of the 110 displayed, but I also wondered about what happens if either the pump is not pumping or the thermostat stays closed, I guess the actual water temp in the engine would get hot but the water in the swirl pot would remain colder, is there anyway without removing or replacing both that I can test to see what is happening?, I guess an airlock could also show a similar issue?
Any thoughts welcome, I don't want to risk just assuming it's a dodgy gauge.
Thanks
Paul

bobfather

11,171 posts

254 months

Wednesday 10th February 2016
quotequote all
Is the 'cold' level in the expansion pot approximately 1/3 of the way up. That's where it needs to be to cope with coolant expansion. If it's lower you risk drawing slugs of air into the system, level is critical. If that's okay and you're not ejecting steam from the pressure cap then you should be okay to look elsewhere. Open the swirl pot, coolant should be brimming. If there's a few cm's of air then you need to prime it. Once those bits are right then look for something else but you should know that the sender for the dash gauge is poorly located and therefore unreliable. Search for 'Rover temperature mod' for ways to improve that

Paulprior

Original Poster:

864 posts

104 months

Wednesday 10th February 2016
quotequote all
Hi, the expansion pot is about 2/3 full, I don't loose anything out of the pressure release, I haven't checked the swirl pot level, I will do so.
When the stat opens should I be able to feel the hoses to the radiator expand / pressurise?
I have read up quite a lot on the subject and read a lot about reading from the other sensor, but haven't really read much about people actually doing it, is it recommended?
Thanks
Paul

QBee

20,904 posts

143 months

Wednesday 10th February 2016
quotequote all
I think your gauge is reading high.
Standard otter switch, fans come on and go off again, all points to normal operation of the cooling system.
If you have Rovergauge you will have a double check of temperatures.

bobfather

11,171 posts

254 months

Wednesday 10th February 2016
quotequote all
2/3 full is too much and could indicate that you have a slug of air. As the slug passes into the pump the flow stalls causing local boiling around the cylinders. This will hiccup the system causing liquid coolant to belch out of the pressue cap and also kicks coolant flow to restart. You won't see the coolant loss because it's liquid. This will also cause large variations in temperature, you state that you're seeing this

If this scenario is correct then you will have air in the swirl pot

ClassiChimi

12,424 posts

148 months

Wednesday 10th February 2016
quotequote all
You could really do with plugging into a rover gauge and getting the readings from the Ecu, my gauge pre Ecu upgrade would go upto 110 regularly, before fans kicked in, rover gauge confirmed fans kicking in at about 88-94
If you have a constant water level, no sounds of pressure or bubbling, heater should be toasty when hot etc I'd say the temp sender is just to hot, I've not done the mod myself but there's plenty of info. Check your oil looks good too, if it's to hot it will start to smell and dink in the engine bay,, that's simply to hot.
Do your fans kick I and out then stay off awhile or come back on regularly, obviously speed and air flow will dictate a lot of this but if your regularly moving along at say 30mph they should generally stay off this time of year. Maybe an indicator of radiator flow etc if there coming on a lot.

Hedgehopper

1,537 posts

243 months

Thursday 11th February 2016
quotequote all
Not sure if the Chimaera is the same but my Griff has a bleed plug in the side of the radiator. After re-filling the system it requires to be bled after the first two or three runs. There is also a 16mm blanked off hose from the top of the n/s inlet manifold, this also makes a good bleed point.

TV8

3,118 posts

174 months

Thursday 11th February 2016
quotequote all
An easy test - have you felt the thermostat opening properly - run the car up from cold and feel the thermostat open and the pipe to the rad go from being luke warm to the touch to very hot in a few seconds?

I have found the IR gun to be useful to compare temperatures at different points in the system, rather than absolute temperature.

Paulprior

Original Poster:

864 posts

104 months

Thursday 11th February 2016
quotequote all
Hi
How do you 'feel the thermostat open'?
I understand feeling a fast temp change.
I have ordered a rover gauge cable as well and see how I get on with that
Thanks
Paul

bobfather

11,171 posts

254 months

Thursday 11th February 2016
quotequote all
It really is worth doing the Rover temperature mod. You see from this image that the TVR sender is located in an extension tube that causes a dead spot where the water temperature can be cooled or heated by adjacent engine parts without reference to the the actual coolant temperature. The mod transfers the sender cable to the unused Rover sender which is located next to the ECU sender and therefore responds in line with the ECU sender and RoverGauge output. The TVR & Rover senders are different so you need to add a 160ohm resistor in the sender cable to compensate.


Paulprior

Original Poster:

864 posts

104 months

Thursday 11th February 2016
quotequote all
Hi, I will try the Rover sense then with a 160 ohm resistor, but if I find that my gauge is also a bit dubious after checking against a reading from the rover gauge could I replace the fixed resistor for a variable one and tune the output to match actual temp and the gauge display?
Thanks
Paul

bobfather

11,171 posts

254 months

Thursday 11th February 2016
quotequote all
The variable resistor method has been done successfully though it's not reliable long term as the engine bay is hostile. Using the variable resistor you can adjust to the reading you want, remove the variable resistor and measure the actual resistance then purchase a fixed resistor of that value. You may need a couple of resistors wired in series to get it precise

Paulprior

Original Poster:

864 posts

104 months

Thursday 11th February 2016
quotequote all
Sounds a good idea, one final thought, how do I connect to the rover sensor?, it's not a nice simple spade type as I can see?

bobfather

11,171 posts

254 months

Thursday 11th February 2016
quotequote all
It's a standard female bullet crimp. For the money it's worth popping a new sensor in there. They're only a few quid and you don't have to worry about the corroded connector

Paulprior

Original Poster:

864 posts

104 months

Thursday 11th February 2016
quotequote all
I guess that's a standard Land Rover part then?
Thanks
Paul

bobfather

11,171 posts

254 months

Thursday 11th February 2016
quotequote all
They all appear to be after-market now. I just searched 'Rover v8 temperature sender' and chose a supplier I could trust

Paulprior

Original Poster:

864 posts

104 months

Thursday 11th February 2016
quotequote all
I guess that's a standard Land Rover part then?
Thanks
Paul

Bassfiend229hp

5,530 posts

249 months

Thursday 11th February 2016
quotequote all
Remember that unless the gauge and sender are matched then even if you do the resistor mod the gauge will not be accurate and will (at best) only be correct at one temperature ...

What's the thread on the Range Rover sender position? 1/8 NPT?

Phil

Paulprior

Original Poster:

864 posts

104 months

Thursday 11th February 2016
quotequote all
Hi, I assumed the 160 ohm resistor was to match the sender and the gauge, is that not the case?

blitzracing

6,387 posts

219 months

Thursday 11th February 2016
quotequote all
The problem you have is the temperature sensor resistance does not change in a linear manner against temperature. Ideally the gauge and sender are matched to suit this response- but when you add or remove resistance you can set the temperature reading at a fixed point, but it skews the shift of resistance across the sensor so above and below this fixed point the reading will be out. You can equally well put a variable resistance at the back of the gauge and simply tweek it to give a sensible reading at say 90'c.