Coolant temp sensor question

[LeesTruk]

Is anyone using the '98 Camaro/Firebird cts for their LS swap and is it compatible with the squarebody temp gauge? Before I drill and tap the hole in the pass. side head, I'd like to try this route if it's feasible. I've used the search directory here and either I'm not asking the right question or no one has gone any farther than to say it should work. I'm just curious to know if the thermal resistance is similar between the original sender and the Camaro unit. Thanks

Later...

Lee

[clinebarger]

I have used them in the past, They rarely/never work correctly. I have used resistors to up the resistance to get the gauge to read half way at 210°F, But the Scale/Sweep is still off.

If it helps, The '98 3-wire CTS puts out (approximately) 1365 ohms at 100°F & 55 ohms at 260°F on the gauge wire.

Never had an issue drilling & tapping the head (3/8" or 1/2" NPT).

[LeesTruk]

Thanks. Now here's a hypothetical for you. How much resistance is in the wire that the points ignition trucks use? I imagine it's measured by the length used. It's just a thought, as more than likely I'll pull out the trusty DeWalt and do a little drilling

Lee

[68c10airstream]

Lee, how i addressed this issue with the 2001 in my 68 c10 was this way. I drilled the face of the truck water pump and installed the 68 factory sender into the water pump because i wanted to use the stock cluster. Once the engine was in and running my stock gauge was reading a full 3/4 scale if not more. I cut the wire about a foot back from the sender, installed inline a variable resistor and dialed in my stock gauge to read 1/2 scale at 195 degrees, (another words added additional resistance inline). Removed the variable resistor and measured it. In my application it was 4 ohms. Went to radio shack purchased a 1/2 watt 4 ohm resistor and soldered it in with adhesive lined heat shrink tubing and all is good. Good luck, Brian F.

[LeesTruk]

It's interesting to see that a simple t-stat relocation would cause such a discrepancy in your gauge reading.

Lee

[68c10airstream]

The way i looked at my stock 68 gauge cluster is this way; how hot did a 1968 engine run? As a tech in auto schooling in the late 70's engines prior to 1975 ran in the 170-180 range and if they hit 200 degrees it was very hot and the gauge would show it. In 1975 with the introduction of catalytic converters the thermostat temp increased to 195 to help light the cat (get it hot to react) but prior to that time the engines ran cooler. So using the stock sender and gauge i skewed it lower through the use of a resistor, back to a normal mid scale reading. Re looking at this scenario i could probably go to a square body cluster from 1976 and newer, remove the resistor board from the rear of the temp gauge and possibly swap that over into my 68 temp gauge and it would read correctly. This would be under the premise that both temp gauges had the same internal resistance and the temp senders were the same. My 4 ohm in line resistor was a quick way of dealing with this. Through all of my years working on these trucks with low gauge readings and living in the salt belt the first course of repair for a temp gauge reading low was to clean the head of the sender terminal that is exposed to salt and oxygen. They typically were green from corrosion as these were not a weather tight connection and the corrosion added resistance and skewed the gauge colder than the engine really was. I would verify the engine thermostat was working correctly with a thermometer in the top of the radiator. The truck owner judged the engine temp based on what he saw on his dash gauge so i addressed both scenarios with one visit. Hope this long story helps, Brian F.

[68c10airstream]

I should add that the reason i installed the temp sender into the water pump face instead of the cylinder head was 5 years ago when i did my swap i didn't find anyone that had drilled the cylinder head out and tapped it substantially larger, and the face of the water pump has a flat boss perfect for this and i think street and performance did it exactly this way.