VDO temp gauge

[reborn55]

Coming back from a mall show tonight, watching temp gauge, blower not on, just driving, temp around 200, turn the blower on and temperature on the gauge starts going down. Turn the fan off and temp climbs--starts going close to 230--turn the blower back on and temp starts going down below 200 and stays there. so bad gauge or wiring problem--I have been fighting what I think is higher than normal engine temps since I have owned the car. VDO cockpit royale electric gauge--would love to find a mechanical gauge and not worry about it. rest of the gauges seem to work OK--although volt gauge does go down to almost 13 volts with lights and blower on. any help as usual is appreciated. Thanks

[wayne petty]

run additional ground wires between the back of the engine and the firewall....    or the main part of the body tub...



the engine is sitting on rubber mounts...

the battery positive is connected to the starter.. alternator output. and fuse box.... ect...

the battery negative is connected to the engine block...   hopefully the body in a good enough place to supply grounds to the headlights and anything else grounded to the body..

there is on most OEM builds... an additional ground strap between the engine block and the firewall.. this properly grounds the motor..


with a digital volt meter you can test the grounds in under 2 minutes...

set your digital volt meter to 20 volts DC  ......

start your engine and turn on the headlights...  and any other accessories like your heater fan....


1.  measure across the battery positive to negative... you should have 14.1 to 14.6 volts...

2.  measure from the negative battery post to the engine block... a reading of 0.04 volts DC is expected....

3.  measure from the negative battery post to the body...  a reading of 0.02 volts is expected...

4. measure from the engine block to the body... a reading of 0.02 volts is expected...

if you get more than the 0.02 or 0.04 readings you have a bad ground between those points....

if you get a reading of 0.00...  there might not be an electrical load flowing between those parts..

why is this important.. and the first thing to do...

Electrons flow from negative to positive...

if you have a bad ground...   you may not have enough electrons to power your circuit properly..


since the dash gauges are grounded to the body... and there is only one wire to the temp sender...    if there is a ground difference.. when you apply load elsewhere...  you change the voltage between the parts on the ground side... so the gauges will change....

[38HAULR]

The fix for this is to regulate the gauge voltage. Keeping it constant and sheltered from the rise and fall of your vehicle voltage under various load conditions.
This is standard practice for factory vehicles .
Not up with modern cars today.  But the normal gauge voltage for factory instrument clusters is 5v.  They used a bimetallic mechanical  regulator into the 80,s.
Modern vehicles would now be electronic.

The first clue I had with instrument regulator failure was with my 66 Mustang, the temp gauge was noticeably climbing with acceleration and dropping on idle .
I would certainly make sure all your connections are tight as described, and monitor the battery terminal voltage on idle   then -- increased rpm-- then - full load lights/accessories on.  You may have an alternator /reg problem or an alternator not coping with load.
Frank.

[Rrumbler]

Sounds to me like you may have a marginal radiator, or thermostat, or some blockage of some sort that is impeding water flow.  I had a '57 Chevy with a cell type radiator that was damaged by a fan blade blow-up, and it lost about a third of the radiators capacity; I crimped off the damaged cells, and ran with the heater and fan on all the time until I could get a new radiator and replace the fan, and the heater acted like an auxiliary radiator and helped keep the temp in a reasonable range.  If I turned the fan off, the temp would go up.

Just a different point of view from a guy with long white whiskers.

[1800guy]

What Rrumbler said sounds good to me.  More than once I've used my heater as an emergency cooling system helper.

[reborn55]

Brand new super stat--180 degree thermostat and brand new Walker  Radiator.  Will check electrical aspects this weekend
Thanks

[Ed ke6bnl]

What Rrumbler said sounds good to me.  More than once I've used my heater as an emergency cooling system helper.

I did that also towing up Sherwin Grade to the Sierras only to discover later that turning on the heater also fired the Air conditioning kinda negating the all the effect of the heat in the cab. next time pulled the wire on the ac. AND later put in a new factory clutch fan that solved years of overheating issues. ED some vehicle do not work this way

[40_Tudor]

Where is the temp sending unit installed? Should be in the head for SBC.
Also did you use any Teflon tape or sealer on temp sender? If you did take it out and clean it off and reinstall with out any tape or sealer. It won't ground write with sealer or tape.