Fuel Gauge Year Breakdown

[thefraze_1020]

Ok, so I've read several threads and write-ups about how do tell the difference between tachometers and speedometers from various years, but can anyone shed some light on fuel gauges?

I know the difference between 73-79, and 80-87 (91) fonts, but I've seen some with "E" and "F", tank symbols, some with "unleaded fuel only", "diesel fuel only", or just "diesel", or just blank.

Is there a rhyme or reason to these variations (by year, model, etc)?

[ray_mcavoy]

You're right ... there were many variations of the fuel gauges used in these trucks.

I believe the change from the word "FUEL" to the little gas pump symbol took place right around the same time as the font change. The change from the E, 1/2, and F markings to the partially filled circle symbols was later ... I'm not sure of the exact year but I'm guessing that was around 1986 or so.

The "unleaded fuel only" label started appearing on fuel gauges in 1975 on trucks that were equipped with catalytic converters. Trucks that were above a certain GVW (varied by year) were considered "heavy duty" and did not require catalytic converters ... they continued to use the fuel gauges without the unleaded only label.

I'm not sure about the difference between the gauges marked "diesel" vs. "diesel fuel only".

[thefraze_1020]

The switch to the tank symbol in 1986 seems about right. My 84 has "E" and "F", and the 88 Suburban we used to have had the tank symbols.

[lowrodderchev]

so figured I'd piggy back his thread. I'm running a 87 sender in my 75 blazer (did a LS swap) I know I already needed a new gauge so does the 75 gauge work with the 87 sender or will I have to get a 87 gauge? thanx

[hatzie]

Up to 76 you could have 0, 1, or 2 warning lamps at the bottom of the gauge. The wiring diagrams don't show the warning lamp sockets in use till 1976 but the printed circuit has provision for them. Not sure if this is a LD vs MD thing where the MD trucks had more lamps.

Unleaded happened in 1974 & 1975 on the 1/2 tons and later on the 3/4 & 1 tons. No doubt this coincides with the presence of a catalytic converter.

If it says Diesel it's at least a 1978 gauge.

I had a 1985 that still had E & F. I was not the original owner.

The sender is 0-90ohms for all 18 years of this body style. An original 1973-1975 sender may actually more literally track the actual tank volume than the later senders.
Why? I remember reading a Chevrolet Service News article that stated customers were complaining about poor fuel mileage. The article stated that GM has started changing the fuel senders in all their products to sweep the needle slower for the first 5/8 of the tank. This is why it seems the fuel gauge drops from 3/8 to E much faster than F to 3/8... it does.

[lowrodderchev]

Thank you for the info guess I'll be ordering a 75 fuel gauge

[hatzie]

The sender is the thing that changed.
The replacement senders are all weighted. The only way to get the older linear sender is cannibalizing a 1973-1975 that still has the original sender.

[lowrodderchev]

Originally Posted by hatzie

The sender is the thing that changed.
The replacement senders are all weighted. The only way to get the older linear sender is cannibalizing a 1973-1975 that still has the original sender.

but I could get away with running a 87 sender to a 75 gauge

[hatzie]

Yup. Fuel and electric oil gauges are the same for all years.

The only thing on the panel that gets mildy obnoxious is the Temp gauge. There are at least 5 different senders. The early nail head temp sender is obsolete.
All years temp gauges will work with all five different senders but differing sender thermistors will place the needle in slightly different positions. The later panels have C & H rather than actual temps. Really the temp gauges are just a guide. Watch where the needle goes when it's operating normally and pay attention to whether it's consistent.
If you just have to have the temp gauge spot on look up "Letric Limited Nailhead Sender" on Google. They make a Nailhead sender that matches the obsolete GM nailhead sender curve. No other replacement can say that including AC Delco. They also have a two or three page explanation of how their sensor is just the best thing since sliced bread. If you just want the temp gauge to work and aren't worried about calibration put a Delco sender in and go.