herald reads hot....

[mishmosh]

My Herald has run its MkIV engine for 28 years. no probs.  recently noticed it mostly reads very hot but no other problems, so decided to sort it. Flushed the system with radflush, which showed a slight leak on pump. So , I replaced. Pump, thermostat, rad cap, sender unit. all with new. It now reads even higher ! doesnt appear to be losing water. Doesnt appear to be particularly hot. Top of rad hot, bottom cool...... Guage reads into or just below red. 

I assume next job is to try a different Guage? but there has to be a better way ?   

[AndyTV8]

Try checking with an IR thermometer to see if you actually have a problem, if not I'd change the sender first

....... Andy

[JohnD]

Agree with Andy.

Published this before, but anyway:

Purple as it should be.

Yellow and Blue, old,but I've seen this on three month old sensors.

 

JOhn

 

[david lewis]

same thing happened to my 13/60 ,went through same checks and new parts plus new rad. eventually fond the voltage stabilizer was faulty giving a high reading.

i fitted a new electronic one off ebay and no more problem.

[Darren Groves]

same thing happened to my 13/60 ,went through same checks and new parts plus new rad. eventually fond the voltage stabilizer was faulty giving a high reading.

i fitted a new electronic one off ebay and no more problem.

Would give a high reading on fuel gauge also if this is the problem.

[Pete Lewis]

The stabiliser is the first call, thats if its got thermo bimetal gauges the slow resopnding needles

these use sender gtr108

 

if its older with moving iron gauges( the ones with quick and waggly needles)

then you need a different sender 121997

 

if you get them incorrect supply or intermix the two designs you get high readings near the red.

 

Not all electronic voltage regulators control a stabilised output its just reduced and thats not going to stabilise the variation in driving votages you get.

[mishmosh]

i havent suspected stabiliser as the fuel guage is so accurate. but will certainly try it ( think I have a spare somewhere .) Trying a spare guage on wednesday club night. so that will help. Its a new sender and reads same as the old one.  

Thanks John, but beyond my tech expertise !  I agree that a IR thermo is the answer , and will explore that after wed if all else fails . 

The Radiator was recored when i boughtb the car as a wreck in 85 but appears good . I suppose its possibly blocked.but as mentioned, the engine doesnt appear overly hot. 

 

thanks chaps.  

[Pete Lewis]

Or get a cheap thermometer from the chemists and stick it in the rad filler

 

it should read as the stat you have fitted close to the std is 82c

 

Maybe its time to replace the thermostat,

 

senders used to be colour coded by smiths but all noe seem the same

 

does your sender have some numbers on the hexagons ? Was it boxed, do you have thebpart number ??

pete

[JohnD]

 

Thanks John, but beyond my tech expertise !  I agree that a IR thermo is the answer , and will explore that after wed if all else fails . 

 

Don't sell yourself short, Mish!

 

How I tested those sensors was very simple.     Camp stove on bench; battery set up to energise a sensor, gauge and volts regulator, with the sensor under test held in a water pan on the stove.

Multimeter set up to measure sensor resistance.

As it happened, the multimeter I had then had a temp probe of its own, so I could switch from Ohms to degrees C with a click of the rotary switch.

As you say, an IR gun would do as well, but paint the inside of the pan black.  Guns don't do well on a shiny surface.

Pic below.

John

[mishmosh]

Tonights update ! swapped rad for a known good one. Read Hotter !  Grr. top of rad very hot. Bottom 

very cool. Took the new  thermostat out. Now runs ( as expected ) cool on guage. . Rad hot at top , warm at bottom. 9 .....as expected) So it may well be a thermo problem.  Going to try the lob it in a pan  test if i can find a thermometer. 

[Pete Lewis]

Just dont boil ot like an egg, raise the temp in small increments , you, looking for the start to open point

if its boiling you cant see.

 

we had a tank with impellor and it raised temp in 10ths of a degree to test these

 

in the car these opennand close to modulate the temperature all the time , they dont just open and stay open , as cool entrers from the rad they close down till re heated and then re open so they work a lot

I would just replace it , its the only temperature control you have ,

 

make sure any replacement has a bleed jiggle pin in the rim , lets air out when its closed ,if its missing drill, a 3 mm hole in the rim

[mishmosh]

Just dont boil ot like an egg, raise the temp in small increments , you, looking for the start to open point

if its boiling you cant see.

 

we had a tank with impellor and it raised temp in 10ths of a degree to test these

 

in the car these opennand close to modulate the temperature all the time , they dont just open and stay open , as cool entrers from the rad they close down till re heated and then re open so they work a lot

I would just replace it , its the only temperature control you have ,

 

make sure any replacement has a bleed jiggle pin in the rim , lets air out when its closed ,if its missing drill, a 3 mm hole in the rim

its bloomin new   

Paddocks, so should be ok . going to test it anyway. gave it a good run tonight with no stat.   Stayed very low as expected, with minimal heat from the heater. so suspect it is the stat. odd as thats the one that was in and the new one ???

[Pete Lewis]

Did it have a bleed hole ??

 

once a stat has been over heated they tend to go out of calibration

If it suffered an air lock on initial running it may have upset the wax settings. They are a very simple bit of kit but can go wrong

 

pete

[mishmosh]

I have bought a 72 degree summer stat. Going to try that and get a winter stat for .....er winter. 

[Pete Lewis]

In reality There is only one std is 82c from the uk parts lists the 88 or 78 and 72 are for counties with more extreme climates not for the UK.

theres no such winter or summer as a UK spec and as running cold needs a richer mixture and whilst there are no HC CO figures for the cars till later , being richer will induce pinking and poor economy

 

88 would not be used in the uk till leaner burning of the mid 70s evolved you would end up lean and burn the exaust valves on older spec engines

 

Just some thoughts

 

Pete

[mishmosh]

Ok, Tonight I fitted the 72 degree. Guage reads perfectly ( I expected it to read cooler.). Next job is to swap the guage and see if it reads differently....

[Pete Lewis]

Pity your too far away I have a Smiths test kit

nice wooden box does all iron or bimetal fuel and temp gauges and their senders

for all settings , , saves guessing

In the end a correct sender , working stabiliser and 82 c stat should read with needle between the two small dots on the face of the gauge

 

pete

[mishmosh]

Thanks pete. I do get to Cheshunt on a regular basis , so if all else fails ....!

[Pete Lewis]

sent you a PM

 

Pete

[gt6chris]

Just been through the same thing with my TR6. It was reading hot and on the motorway got even hotter. I suspected a silted up rad. Having replaced the rad I took it for a run with out the thermostat fitted and as expected it ran cool, the temp gauge only getting just above the cold section. I refitted the correct 82 degree stat and it was reading 3/4 up the gauge ie hot. I now decided to get scientific and set up the temp transducer in a pan as per Johns instructions (I was home alone so in the comfort of the kitchen). I plotted a graph of the resistance against temp. I then purchased a 1Kohm linear potentiometer from Maplin and set it to match the various temperatures taken from my graph in place of the original sender so that I could see what the gauge read. Everything seemed to tie up, around 85 degrees was 145 ohms on the transducer and gave a mid point reading on the gauge. Once reassembled and test driven the temp gauge remained pretty much central (this was with a new sender that I had used to plot the graph). I will swap the original voltage stabilizer for a solid state device as they seem more reliable and you can easily check the output voltage as it is stable rather than an average that you see on the mechanical type.

 

Graph of temp/resistance

 

 

[mishmosh]

Update.   The 72 degree behaves well On my original guage, it sits in the middle. On a borrowed guage, it sits below( where expected)  I plan to get a new guage ( unless I can cheaply calibrate mine ) and then put the correct thermostat in. 

[Pete Lewis]

Easy enough to reset the needle position, hardest part is getting the old rubber ring to let go and turn the rim to enable removal of the inards,

 

some version of bi metals have a setting screw locked with threadlok others are in need of

finger ingress and a small plier or tweaser to upset/reset the needle position

 

Pete