HI,
I replaced the temp sensor due to it reading really low when warmed up. The new one came from WCCC, and now at warm idle, the temp needle sits to the right of the P in TEMP. Just to the right.
However, when driving, the needle does higher and approaches the H section, without actually going into the HOT zone.
I have topped off the radiator with 50/50 and replaced the thermostat with 180 F temp model.
Looks like the radiator is the original one, or has been in service for a long time.
I did open the cap after warming up the car and take the temperature of the AF and it showed 179 F, so I think the thermostat is working good.
Should I worry about the needle creeping up higher as speed goes higher? It never actually got into the HOT zone, but it makes me nervous on longer drives.
I have had exactly this same thing happen with my 68 XR7 and with my 79 bronco as well. The bronco actually makes it up to the line on the hot side and even past it, nearly pegging the needle. But a laser temp gauge confirmed normal temperatures.
I haven’t tested this theory yet, but, my gut tells me the issue is either with the resistance of the circuit changing over the decades, or, the one I feel is probably more likely, the voltage regulator that controls the instruments supply voltage changing over the decades.
I haven’t delved into it yet to see, but if there is any electrolytic capacitor involved in filtering the DC voltage that feeds the gauge, that would be the first place I would look. Electrolytic capacitors (or condensers as capacitors are called in the car world) have a relatively short lifespan. Something like 15 years max expected lifespan if they see regular use and as little as 10 if they are disused. So a 40+ year old electrolytic capacitor has almost no chance of still functioning as it should.
I wish I had my shop manual handy to check if there is indeed an electrolytic cap in the voltage supply for the gauges. If there is, and it’s stock, I would say the chances of the gauges reading correctly is pretty much zero.
Would the capacitor at the voltage regulator at the front by the headlights be an issue? I have replaced the regulator, but not the little capacitor that is there.
Hmmmm.
Yeah that capacitor is a pain. That’s what went wrong with my voltage regulator, that and some corrosion on one of the terminals. I replaced the whole thing with a solid state unit and haven’t looked back.
If that capacitor is bad, then if your car does what mine did, the lights will pulsate as the regulator switches back and forth between charging and not charging the battery-- that capacitor is there to smooth it out as far as I know.
I wouldn’t expect any gauges to work correctly with that capacitor non functional, UNLESS there is a separate voltage regulator for the instrument cluster which I thought I remember reading somewhere. If that’s the case, then you’d want to make sure that regulator (and any associated cap) was functioning properly.
I’m surprised others haven’t been chiming in on this one. I know there are guys here who know this inside and out
The capacitor at the voltage regulator is simply a noise suppressor for the radio. It has no bearing on anything else. There is an instrument voltage regulator attached to the back of the dash gauge assembly.
The real way to trouble shoot this is to look at the resistance across the sending unit at a specific temperature. I think there may be a spec in the factory shop manual. At any rate, the needle should point to a specific point on the gauge at a specific temp, but they were never that accurate. The place to measure the temp is at the temp sensor location, not the radiator. If you ver very carefully take apart the gauge, you will find an adjustment.
If you have Teflon tape on the threads of the sending unit on the intake…remove it and thread it in tight with no tape or sealer. The tape will create a poor connection and throw the resistance readings out of wack!
I remember finding a chart of the resistance values and associated temperatures online for the 351m when I was going through all this with my Bronco. I don’t know about other engines, but I assume they’re out there too. Probably on a Mustang site somewhere.
