Mr.Gearhead

Okay... so I have never put this much time and effort into something so simple... but it has been enlightening to say the least.

I just called Borg Warner and gave them part number WT203. I requested technical specs to see if it was deltas in manufacturing...

standard reading 368ohms
220* reads at ... 80ohms

I informed him that it is understood that the gauge requires 79ohms to read 210*... no response.

I asked if there was someone else I could speak to about the possibility of inaccurate output... no response

I simply said thank you for the help and he replied "your welcome"

0Willcox Corvette

OK.. what Roger is doing.. he's not inputting resistance in the green wire.. he's changing the resistance on the back of the dash unit.

The dash unit has a 90 ohm resistor to ground and Roger has removed this resistor and then inserted a linear pot in place of it. This allows him to adjust the ohms to ground and make a running change in the way the dash unit works. Knowing the output of the sending unit will allow you to match the gauge to the sender.

Rogers pot is not on the green wire to the dash unit!..

Willcox

0Willcox Corvette

One thing you have to always keep in mind... Not all dash units are the same in what is required per gauge. They will vary from gauge to gauge depending on the gauge condition. Even with GM there was an allowable margin for error in the gauges. Being able to dial in the ohms to make the gauge read at fixed points will help you establish what the specific requirement is for "That" gauge. Once you know what is expected for the gauge you have to either find a sender that will match this or manipulate the gauge to match the sending unit..

I'm pulling my chart down from the site this evening.. there are a few errors in there that are typo's and one thing that I've forgotten about is the 63-65 temp gauges were not screened properly from the factory.

Willcox

0Willcox Corvette

But.. that is within the GM margin for error when the cars were built. I pretty sure the over under was +/- 10 percent.

Mr.Gearhead

I hope my sarcasm about Borg Warner has not influenced removing the page on temperature gauges. I think this is good baseline data....

My true sarcasm is how all these sending units are all over the place with their output... I suppose I expected a little more accuracy considering importance of temp reading.

I think Roger's test yielded excellent results and this is a good topic. BWD seems/has the most accurate sending units of the bunch for our application and with some tweaking the gauge could be real close. I am going to test my gauge this weekend to find out the ohms are required to hit the marks. Then see if I can get it all calibrated...

I know 210* is going to be real close to 79 ohms

0Willcox Corvette

Gearhead.. your comment didn't bother me.. There is are two typo errors in the data for other gauges..

I need to fix this. Looks like this will be my tomorrow job now..

baxsom

OK so let me make sure I am reading right. I have a LL temp gauge sender in my 72 BB. The temp gauge settles around the 1/4 mark. Is my engine running hotter or colder than it is showing?

...Roger...

I suspect its running hotter , but you need to check it with a temp gun to be sure.
Thermostats in general are pretty accurate ,what thermostat do you have in yours ?

0Willcox Corvette

Hey Roger-

Nice talking with you again today! As always, very enjoyable!

Baxsom-

Are you sure the gauge is working properly. If the gauge's highest reading is 1/4 this usually indicates the gauge has a cooked resistor on the back of it..

So.. before you start testing.... remove the ohms wire from the sending unit and see if the gauge goes to cold, then ground out the ohms wire from the sender and see if the gauge peg's hot! If it pass's this test then your gauge is working fine. If the highest it will go grounded out is 1/4 then you have a blown resistor on the back of the gauge.



Willcox

Danish Shark

Good work
Maybe this should be a sticky?

73StreetRace

Hey, Roger !
Did you check if the battery voltage has any influence on the readings or not ?
I mean, is there any difference when battery voltage is 11.5 volts ( engine off ) or 14 V ( alternator charging ) ?

...Roger...

Hi Ernie,

Same here , always a fun and informative discussion. You were right , searching for a potentiometer is much easier online. The surplus place had zillions for $ .25 each but most are just thrown in boxes and all mixed up.
I bought one that I could permanently attach to a gauge but it is small , .5 watt (not 5.0 like you said)and 200 ohm. Instant smoke ?
I'll set it up on a gauge and leave the input signal open, that should make the pot max hot,right ?
Roger

...Roger...

No I haven't but have heard that is a factor.
When testing the senders in boiling water my ohm meter was the only thing connected to the sender.
When attached to the car , the engine was running most of the time.
When the engine was turned off and the key turned back on immediately the reading remained very close but would creep up , (assumed this was heat soak).
I will run this car today ,note gauge reading and measure voltage and then unplug the alternator note gauge and measure voltage. I'll report back.

...Roger...

IMO a 1/4 mark reading could be from:

#1- A sender putting out an ohms reading around 109 when it should be 79 ( typical of the LL senders I've tested)

#2 ---------------

#3----------------

#4- No thermostat or a 160 degree thermostat and the engine is just running cold.

EDIT- I removed #2 and #3 from this post because I believe them to be wrong.

Baxsom-do Ernie's ground and unground of the green sender wire-this will tell us a lot.
Then try and get us an ohms reading from the sender with the engine at normal operating temp. If this reading is higher than 100 then this would explain the low temp reading.
I believe a good standard test is to put the sender in boiling water and read the ohms. It needs to be round 80 for a good gauge to read correctly.

...Roger...

I had a request to reinstall the LL sender since I had changed the resistor on the back of the gauge to see if it would read more accurately. I started to explain by email the 102 ohms reading from the LL sender in boiling water would only make the gauge ........ blah blah blah ... crap........I really didn't want to remove the shielding and drain the coolant but I said what the hell it will probably take less time to just do it and take a pic than to try and type it out. So here is the car fully warmed up idling with a temp gun reading of 207 and the LL sender reinstalled.

...Roger...

WT 203 back in.

...Roger...

I measured the voltage at the back of the alternator at 14.1 , unplugged the alt and voltage measured 12.3 . There was no visible difference in the gauge reading. In fact in the pic above I have the alt unplugged so the gauge is operating off 12.3v.

0Willcox Corvette

Roger- You need to start vacationing in Sunny Jeffersonville instead of that state down south! Then.... I'd put you to work..

You are correct, the flux in voltage not make that much difference.

I'm going to dig up those pics of the test Pot on the gauge for you tonight if time permits.

Ernie

shrekviper

Hey, that's what mine looks like. Never gets higher. Time for a new sender I guess. Thanks for this thread.

...Roger...

Your welcome , its been fun except for the coolant in and out.
Check your engine with a temp gun first , some small blocks with a stuck open thermostat will run about there.