1970 fj45 gauges, voltage surge (1 Viewer)

[iananderson]

Hi all, i have been trying to fix this problem but cannot find any thread with the same problem. The old owner changed all the gauges to aftermarket but i have changed it back to original. I have got all of them to work after alot of work but as soon as i rev the engine i lose the engine temp and it just sits above the H, until i don't rev then it reads normal.

I have seen that the fuel gauge regulates the voltage but i dont understand how as its just a common positive and the power doesn't go through that gauge to get to the rest.

I have pulled it apart so many times to make sure nothing is touching it shouldn't but the fact it works when its just idling is tormenting me!!!

Anyone have any clues or ideas?

 

[charliemeyer007]

What is the actual voltage reading at the battery doing at idle and at say mid throttle? This measurement would be done with a nice digital unit, not your dash gauge.

Temp sensor and the gauge are a matched set and needs to be so. I suspect when your alternator is pumping out the charging power like 14+ volts not like 12.5 or so at idle - that the higher voltage overwhelms the temp gauge making it peg.

You might investigate replacing/adjusting the voltage regulator on the fire wall, or adjusting the temp gauge to read normal at the higher rpm's and low at the lower rpm's.

 

[iananderson]

What is the actual voltage reading at the battery doing at idle and at say mid throttle? This measurement would be done with a nice digital unit, not your dash gauge.

Temp sensor and the gauge are a matched set and needs to be so. I suspect when your alternator is pumping out the charging power like 14+ volts not like 12.5 or so at idle - that the higher voltage overwhelms the temp gauge making it peg.

You might investigate replacing/adjusting the voltage regulator on the fire wall, or adjusting the temp gauge to read normal at the higher rpm's and low at the lower rpm's.

Thanks Charlie, i did put a new voltage regulator in last year so I'll check to see what voltage it is out putting. I did check the battery and its exactly as you said, 12 then 14.1 with revs. Can i adjust the temp gauge? Its the real old style which is encased on the back.

 

[charliemeyer007]

I think there was a thread not to long ago about adjusting gauges. I think someone here does re-builds too. Back in the 80's when I put in a 12.5 gallon aux fuel tank from a Datsun B210, I bought an assortment of low value resistors (red line 2%) from radio shack. I was able to get the gas gauge to read from E to 1/2 (full) on the gauge when switched to the aux tank.

 

[45Dougal]

Assuming that you have the right gauges and panel, the fuel gauge does indeed regulate the supply down to about 7Vdc.
Pin '2' is the output to the temperature gauge.
Sounds like the bimetallic arm has welded itself to the contact - make sure the contacts are free, and adjust to achieve 7V.

Better still. Bend it back out of the way, and replace with an external silicon regulator such as a 7807, or 7808 with inline diodes to drop the difference.

 

[iananderson]

Assuming that you have the right gauges and panel, the fuel gauge does indeed regulate the supply down to about 7Vdc.
Pin '2' is the output to the temperature gauge.
Sounds like the bimetallic arm has welded itself to the contact - make sure the contacts are free, and adjust to achieve 7V.

Better still. Bend it back out of the way, and replace with an external silicon regulator such as a 7807, or 7808 with inline diodes to drop the difference.

View attachment 3509645

View attachment 3509646

Thanks but its the earlier style cluster with the gauges only having two connections each.

 

[iananderson]

Thanks but its the earlier style cluster with the gauges only having two connections each.

 

[45Dougal]

Ah OK. Do you have the correct sender for the old gauge?

 

[iananderson]

Ah OK. Do you have the correct sender for the old gauge?

Yeah i have matched up all the correct senders and double checked! I checked all the gauges with a multimeter and the fuel sits around 7.7, the oil bounces around between 2 and 8v and temp does the same but then loses all readings at the gauge.

I checked the regulator and its reading 8v.

 

[45Dougal]

Is it possible that the temperature gauge was switched for a later one?

You could add an external regulator to it if you don't find an alternative.

Maybe worth checking the ground is clean and good at the head - could be that the head voltage is floating a bit I guess.