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Thread: Temperature Gauge Before and after the Radiator

  1. #1

    Default Temperature Gauge Before and after the Radiator

    Hi All

    I decided to put a temperature gauge just before and after the radiator in the hope that it'll indicate if something is getting a bit warm. It may be a bit OTT, but they look good too. Anyhow, after getting them all fitted and wired up, I'm not so confident that they are working right or the wrong senders have been supplied. The temp gauge on the speedo never moves from the middle of the range and has been the same since when i got the car (4.0L V8), The Gauge before the radiator (Top Hose) shows about 115c and the lower Hose(Outlet) fluctuates between 80-100c depending on cruising down motorway or pottering about town. Does anyone know what the before and after the radiator temperatures would be on the v8 or is the normal water temperature higher than i thought?

    The Senders are individually earthed and the gauges supplied with signal, positive and earth supplies. The pictures are of the home made 4 Gauge pod, could not find one to fit the Discovery Dash.

    DSC00670.jpgDSC00680.jpg

    Mike
    1998 Discovery V8 Auto (Horrible Blue according to the Wife..)

  2. #2
    Apprentice davek0974's Avatar
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    Default Re: Temperature Gauge Before and after the Radiator

    The dash gauge does not operate like the accessory gauges, it is designed to indicate 'normal' for a range of temperatures, then go up suddenly on overheat. I think it is done to stop worrying the driver when it goes up and down all the time.

    Your temps don't sound too bad but I can't say good or bad as I don't know the figures.
    Late 1994 Discovery 1, 300tdi ES manual


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    Default Re: Temperature Gauge Before and after the Radiator

    Quote Originally Posted by davek0974 View Post
    The dash gauge does not operate like the accessory gauges, it is designed to indicate 'normal' for a range of temperatures, then go up suddenly on overheat. I think it is done to stop worrying the driver when it goes up and down all the time.

    Your temps don't sound too bad but I can't say good or bad as I don't know the figures.

    In fact the temp drop should be in the range of 15dgc when the fan is working or the ram air effect over the radiator core is adequate.
    What you will find is that if you had some more technical instrumentation like scientific thermocouples the temp rejection of the core actually increase a bit as the temperature rises towards critical. That's of course if you were able to put engine a on "Full Cool" and be able to maintain full power for and extended time --like on a Dyno!

    For what its worth the latter feature of the modern radiator is a Brit design coming out of Manchester and achieved by clever use of fin design.
    As Fred Dibnah would say "Eeh Lad, I bet yah never knew that!
    Dennis
    zedcars

  4. #4
    Consultant listerdiesel's Avatar
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    Default Re: Temperature Gauge Before and after the Radiator

    Sounds normal, our D2 V8 has never varied from the running position of just over half way on the scale, and runs up from cold normally. I do keep an eye on mine, and the water level! It was a new sender when we rebuilt the V8.

    Peter
    June 1999 Disco 4.0 V8 Manual GS on LPG
    email: diesel@easynet.co.uk web: http://www.stationary-engine.co.uk
    V8 Rebuild: http://tinyurl.com/2vee7vz Sunroof: http://tinyurl.com/39d9dfn R380: http://tinyurl.com/32v2r3h
    OBDII Reader: http://tinyurl.com/36r2bv5 LPG Valves http://tinyurl.com/28v943q ABS Mod 19/12/2009 99543Miles
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    Engineer Jimbob292's Avatar
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    Default Re: Temperature Gauge Before and after the Radiator

    I'd double check that top hose temp, 115c on a V8 isn't good, i run a modified rad for the heat, even when its HOT 45c plus, i never hit the 100's, normally around the 94c - 98c in traffic, once up at speed ot drops to a 90c - 92c.

    You might want to drain your system, carry out a good rad flush,and refill.

    Depending where you are in the world, you can dilute the glycol mixture down to around 15 - 20%, this too gives better, cooling.

    Is your viscous fan OK?

    Whats you fuel economy like?
    Discovery 3.9 V8 FXi

  6. #6

    Default Re: Temperature Gauge Before and after the Radiator

    I'm going to check the sender for the new gauge as the outflow from the radiator going down the motorway sits about 60-65c. i think the concentration of Glycol in the system may be a bit high and i'm going to get a tester to check it, as i drained and renewed it not that long ago and it may be near the 50% mark. I'm in Scotland and it's not getting mega cold but you never know.
    Viscous fan seems to work ok as you can hear it when its cold but quietens when warm. The gauge built into the car has never strayed from bang in the middle, summer or winter. Fuel economy, hmm when i was monitoring it, it was between 8-16mpg depending on what i was doing (pottering about or on a long run). it well serviced every year as far as i can
    at the house and a lot or preventative work done as it came in from japan with no rust and i plan to keep it that way.
    Thanks for the replies and look forward to more of them.
    1998 Discovery V8 Auto (Horrible Blue according to the Wife..)

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    Consultant listerdiesel's Avatar
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    Default Re: Temperature Gauge Before and after the Radiator

    The viscous fan should be noisy when hot and quieter when cold.

    There is always some drive to it.

    Peter
    June 1999 Disco 4.0 V8 Manual GS on LPG
    email: diesel@easynet.co.uk web: http://www.stationary-engine.co.uk
    V8 Rebuild: http://tinyurl.com/2vee7vz Sunroof: http://tinyurl.com/39d9dfn R380: http://tinyurl.com/32v2r3h
    OBDII Reader: http://tinyurl.com/36r2bv5 LPG Valves http://tinyurl.com/28v943q ABS Mod 19/12/2009 99543Miles
    D1 Image Archive: http://tinyurl.com/2u2sr9d D2 Image Archive: http://tinyurl.com/3x72fd7

  8. #8

    Default Re: Temperature Gauge Before and after the Radiator

    Quote Originally Posted by listerdiesel View Post
    The viscous fan should be noisy when hot and quieter when cold.



    Peter
    Makes the car sound really meaty and big engined in hot weather, think the boy racer roar it gives lowers MPG compared to cold weather though ! !
    Avatar is us descending Rudland Rigg Aug 2010. Very Good Fun !

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    Engineer Jimbob292's Avatar
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    Default Re: Temperature Gauge Before and after the Radiator

    Quote Originally Posted by karona View Post
    I'm going to check the sender for the new gauge as the outflow from the radiator going down the motorway sits about 60-65c. i think the concentration of Glycol in the system may be a bit high and i'm going to get a tester to check it, as i drained and renewed it not that long ago and it may be near the 50% mark. I'm in Scotland and it's not getting mega cold but you never know.
    Viscous fan seems to work ok as you can hear it when its cold but quietens when warm. The gauge built into the car has never strayed from bang in the middle, summer or winter. Fuel economy, hmm when i was monitoring it, it was between 8-16mpg depending on what i was doing (pottering about or on a long run). it well serviced every year as far as i can
    at the house and a lot or preventative work done as it came in from japan with no rust and i plan to keep it that way.
    Thanks for the replies and look forward to more of them.
    The rad should give a good 10 - 15 TD across the inlet & outlet, i would double check your inlet temp, either a touch probe, laser thermometer etc.

    TBH mine sits just above 1/4 in the winter, and just below half in the summer, since fitting a SPA gauge in the outlet, i only use the LR as a back up.

    With 50% glycol it will lift your boiling point up in the mid 130c's
    Discovery 3.9 V8 FXi

  10. #10

    Default Re: Temperature Gauge Before and after the Radiator

    Hi All.
    Im going to test the concentration and lower it if it is a bit high. I'm not sure about the viscous fan now that the seeds of doubt have been planted. arghhhhhhhhhhh I should just leave well alone. There is quite a temp drop over the radiator so im confident that that's working ok. will let you know how it goes.
    1998 Discovery V8 Auto (Horrible Blue according to the Wife..)

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    Engineer Jimbob292's Avatar
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    Default Re: Temperature Gauge Before and after the Radiator

    A quick way to test the fan, is to get yesterdays paper, with the lump nice & warm, it should show a little sign of lock up, only slightly thou.

    Be careful, try and stop the fan, with the rolled up newspaper, if you stop the fan from spinning, then the viscous fan clutch is U/S, if you can't then its fine.

    But, please be careful, if your not sure, don't do it, always try for the middle lower part of the fan, never the top, as you could smash a few blades off.

    Whats your ambient temp 15c? What radiator grill do you have, do you have any obstructions in front of it, spot lights?

    Do you have an A/C condenser in-front of the rad, is everything nice & clean etc, no restrictions.

    Another quick test is while the engine is running, is spray the hose pipe in front grill and see what happens, with the temp.

    Do you know on what stat you have in, should be a 88c, which by the year in your signature is the same as mine.

    How does your rad cap look?

    Rgds,

    Jim
    Discovery 3.9 V8 FXi

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    Default Re: Temperature Gauge Before and after the Radiator

    Quote Originally Posted by davek0974 View Post
    The dash gauge does not operate like the accessory gauges, it is designed to indicate 'normal' for a range of temperatures, then go up suddenly on overheat. I think it is done to stop worrying the driver when it goes up and down all the time..
    Yep, as long as the acutal temp is within the normal range the needle will stay pointing to the middle of the gauge. Drivers worry if they see the temp gauge going up and down all the time.

    Me I'd rather it went up when sat it traffic (I know then it is working) and drops when the fan kicks in/driving off down the road (again I know the cooling is working).. But then I'm odd
    Other Half to Mrs Dave..
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  13. #13

    Default Re: Temperature Gauge Before and after the Radiator

    Thanks for the info Jim, I have time tomorrow so will do the test you suggest. I have a couple of spot lights and the condenser for the AC, also everything looks clean with no obstructions like mud or dirt or other crud, ambient temp? here in Edinburgh 8-11c tomorrow according to the weather people.
    I'll let you all know and take some pics if possible while carrying out the tests. Gonna dilute the coolant as i think i might have made it a bit strong last week when changing it getting ready for the winter here like last year.
    Regards Mike
    1998 Discovery V8 Auto (Horrible Blue according to the Wife..)

  14. #14

    Default Re: Temperature Gauge Before and after the Radiator

    HI All.
    From the attached pictures, i hope you can see that i have checked the temp as far as i can and have come to the conclusion that the sender or the gauge is faulty or miss reading. Why?
    Firstly, i checked the concentration of anti freeze with a(Halfords) tester and it's in the normal zone, secondly and onwards, tested the sender in a cup of nearly boiling water and the gauge shows 115c (cup1-cup-gauge pictures), Also tested the temperature of the water on the colder side of the radiator with thermometer and as you can see from the Thermo 1-2-3 pictures it's about 65c just after the engine switched off. on the hot side, the same thermometer put in the hole for the sender, shows about 75c

    I'm working tomorrow and have access to a thermal image camera with temperature sensor so will check it at lunchtime to see if the readings are about the same. I'm sure the engine is cooling OK and hopefully the camera will show this. I'll try and take pictures of it and get back to you all.

    regards

    Mike
    Attached Images Attached Images
    1998 Discovery V8 Auto (Horrible Blue according to the Wife..)

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    Apprentice davek0974's Avatar
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    Default Re: Temperature Gauge Before and after the Radiator

    The water in the cup should be reading about 85-90 degrees, it can never be over 100 at atmospheric pressure. Car gauges even accessory ones are notoriously inaccurate as scientific accuracy is not usually needed and costs more to make. I would prefer adjustable digital gauges for super accuracy, they can be set in a pan of boiling water on the stove to 100c which is as accurate as we can get outside the lab.

    I've always wanted a play with thermal imaging, would be very interesting to see some pics, I would like to see the turbo on mine out of curiosity.

    The standard dash gauge with its averaged reading is a pain, I don't want to know its 'ok' I want to know how ok it is! I always snigger when reading about those that take the fan off their TDI and leave it off, they always say the gauge never moves from normal, but that's because it won't until it boils and then it's too late, without a fan damage happens quickly. It also keeps air moving through the bay all the time even when sitting in traffic, this keeps the intercooler cool, without this air, the cooler will warm up giving less boost when needed until it cools down again, plus everything else in the bay gets cooked as well, the fan is there for a reason, but you can't argue when it saves 1hp or so I guess
    Late 1994 Discovery 1, 300tdi ES manual


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