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I'd like to add a coolant temp gauge to my '66 Ninety Eight if possible. I'm thinking about going electric instead of mechanical and hiding it in my glovebox.
Where would be a good place to install the sending unit on a 425?
Keep in mind the sending unit has to be down in the water in the intake manifold or in a cylinder head. The best place is going to be where the sending unit for the idiot light is. I would advise against putting it in the glovebox. Even with the glovebox open, it is going to be difficult to see.
I just replaced the temp sensor in my 98 yesterday , in my 88 the gauge sending unit is connected instead of the
temp sensor and the gauges is mounted under the ashtrey.
I would advise against putting it in the glovebox. Even with the glovebox open, it is going to be difficult to see.
x2
You can use a gauge pod available at your local auto parts store or online and mount it to the bottom of your dash. Even if you don't want to use screws you can use double sided adhesive tape and remove it later without having modified the car.
You either have to give up your idiot light, or perhaps you can find an aftermarket or a newer intake manifold that has places for two sensors in the water passageway (2nd for emissions temp sensor).
You either have to give up your idiot light, or perhaps you can find an aftermarket or a newer intake manifold that has places for two sensors in the water passageway (2nd for emissions temp sensor).
Joe P turned me on to the idea of adding a sensor to the upper rad hose. There's a fitting that mounts to the upper rad hose attachment that you can buy that allows you to run a second sensor here......it's not perfectly accurate, apparantly, but a great backup option. You can keep the original idiot light, or gauge and run this one as a secondary.
If you're using an electric sensor with one of these adapters, note the provision for a ground wire. The hoses obviously don't provide the ground path for the sensor that the intake will.
You either have to give up your idiot light, or perhaps you can find an aftermarket or a newer intake manifold that has places for two sensors in the water passageway (2nd for emissions temp sensor).
On the old V8 cars this is true as there is only one provision for any sender access. However, there is a boss at the back of the intake manifold in the symmetrically opposite location of the heater hose provision that can be drilled and tapped for a sender. If you do that, you can keep the warning light and have a gauge too.
X2 on forget the glove box. A nice two gauge pod for oil pressure and temperature is attractive, functional and reticent if you mount it lower and forward, not under the edge of the dash.
You may want to consider mechanical gages due to the full sweep of the dial.
Use a copper line for the oil, not the nylon.
Last edited by Rocketguy; Jul 6, 2023 at 07:50 AM.
The boss on the back of the intake is also a dead end, no different than using a tee fitting. Flow will stagnate. You'll read something, but accuracy is questionable. Of course, that point is also before the coolant runs through the heads, which are the hottest part of the engine. There's a reason why the OEM port is in the coolant crossover at the front of the intake.
If you're going to drill and tap a place for the gauge sensor, why not drill and tap the coolant crossover in the intake manifold? That's where aftermarket intakes have the second port.
If you're using an electric sensor with one of these adapters, note the provision for a ground wire. The hoses obviously don't provide the ground path for the sensor that the intake will.
I had one of these installed in my '78 Toronado. It worked as advertised, but keep in mind that it is located AFTER the thermostat and thus only works if the thermostat opens. If the thermostat should fail closed, you'll only know because the temperature gauge reading is not rising instead of rising beyond the normal range as it would if the sensor were actually in the intake manifold. So your engine could be overheating, and you wouldn't know it as quickly as you normally would. You might not know it until damage has been done.
I eventually took it out and put the sensor in the intake manifold where it would normally go. There was a place for it because, unique to the '78 Toronado, the normal temp sensor was part of the ignition system, and the sensor was actually mounted on the rear of the manifold close to the distributor. The location at the front of the engine where it would normally go is still there, but it just had a plug screwed into it. I removed that plug and inserted the sensor.
While not the cheapest solution, you could always replace your intake manifold with an Edelbrock aluminum intake since these have two fittings in the coolant crossover. You could even paint it to match your engine.
Again, this is expensive, but you get an aluminum intake out of it, too.
Autometer sells a small electric temp gauge with a built in programmable warning light.
I had mechanical gauges on my car for years. A few years ago I replaced them all with electric gauges and the warning lights. It’s a much cleaner/easier install, and the warning lights get your attention even if you aren’t looking at them.
Kinda pointless putting the gauge somewhere you can’t see it. I’m sure you can find an unused hole under the dash to mount the gauge without making permanent modifications.
I've had a set of gauges & modern radio hidden in my '66 big cars forever. Close the glovebox & it's 1966 again. Open it & you can see what's going on.
Also since the radio is hidden, there's less for a potential thief to see.
At the moment I've got an 02 sensor, voltage meter and temperature gauge in there. Hope you enjoy this picture. Happens to be my Starfire, but my 98 is the same. '66 Big Car glovebox with radio & gauges
A couple of tips
1) You'll probably want to disable the glove box light since you'll have the glove box open a lot more than before
2) If you decide on a 3 gauge cluster mount it into the roof of the glove box cardboard with wing nuts - it's hard to get a wrench up in there.
3) Give some thought to getting a reproduction glove box from Fusick just to start with strong, new cardboard
4) As you go to mount a mechanical sensor, make sure the length of cable they give you (fixed at 6') will reach your glovebox from your intended intake sensor location
5) Be ready to provide the gauge cluster with a connection to your interior lights (the gray wires) so they light up at night with the rest of your dash
I've been through a few gauge brands, but have always trusted a mechanical coolant sensor into the block.
My intake manifold is an Edelbrock Performer which helpfully has 2 coolant temp sensor holes - 1 for the factory idiot light, 1 for the gauge. If you have a factory manifold, I'd go with Joe's suggestion above.
I'm a big advocate for gauges on the idea that the warning lights only tell you when it's too late. On the other hand I can verify that temp gauges make you a bit more nervous and aware of changes to your engine over its use cycle. I've gotten to the point after 40 years that if it's between 165 and 210°F , averaging around 180°F (using 180°F thermostat), I'm good.
These guys are good, more industrial stuff but good line of motosports, race and diesel, Made in Michigan also, very competitive for good stuff. Use there CHT in an air cooled engines,read high temp! https://thesensorconnection.com/prod...ports-products
Should it be possible to mount a sensor who feels
the temp of the metal of the intake behind stat housing ? No drilling only contact with the metal , maybe not so correct readings , hmm.
Did you just drill and tap the thermostat housing yourself? Like drilling and tapping an intake manifold you could even have a shop weld/braze the bung to the thermostat housing/intake.
FWIW, I installed an AutoMeter pyrometer in the exhaust manifold of my 86 Ford F250. Cast iron is quite soft making it easy to drill and tap.
Did you just drill and tap the thermostat housing yourself? Like drilling and tapping an intake manifold you could even have a shop weld/braze the bung to the thermostat housing/intake.
FWIW, I installed an AutoMeter pyrometer in the exhaust manifold of my 86 Ford F250. Cast iron is quite soft making it easy to drill and tap.
Yes drill and tap for threaded adapter, easy to do. I am not sure if the stock aluminum housings could be tapped. This one is cast and aftermarket but works well for a sender.
I did the same thing as Oldsmaniac on a 425 I built for a customer a couple of years ago. He used a mechanical gauge but an electric sending unit would work fine too. He bought an
old school three gauge console and mounted it under the center of the dash. Ill see if he can send me a picture.
Wow! Thank you all so much for all of the incredible info! I'd really like to keep my idiot lights so I guess I need to figure out what route I want to take.
Did you all have to cut a big hole in your firewall for the sending unit? I'd really rather not have to do that if at all possible but it looks like I'm going to. Is there a factory passthrough big enough to work?
Thank you all again, I really appreciate everyone taking the time to help me out with this!
Did you all have to cut a big hole in your firewall for the sending unit?
You need a fairly large hole for a mechanical gauge but there is nothing wrong with modern electrical gauges and all they need is a hole large enough for a wire to go through.
Is there a factory passthrough big enough to work?-Chris
Does your car have A/C? I don't know about the "98" but the Cutlass with A/C has a grommeted hole in the air plenum big enough for the wiring, a copper oil line and the temperature capillary line.
Thank you for the idea! I went outside to check mine out and unfortunately I don't have a hole like that. I do have a hole on the left side of the firewall that all of the A/C stuff goes through but its covered up in the factory seam sealer stuff. I may have to look on the inside to get an idea of the hole size.
-Chris
Originally Posted by Rocketguy
Does your car have A/C? I don't know about the "98" but the Cutlass with A/C has a grommeted hole in the air plenum big enough for the wiring, a copper oil line and the temperature capillary line.
You need a fairly large hole for a mechanical gauge but there is nothing wrong with modern electrical gauges and all they need is a hole large enough for a wire to go through.
Thanks for the info. I'd really like to go for a mechanical because the sweep is so much better but if I can't use an existing hole, it sounds like electric is going to be my best bet.
I am also interested in adding an aftermarket water temperature gauge and oil pressure gauge. By the way, does it matter what type of water temperature sensor and oil pressure sensors you have screwed into the block if you do this?
One reason why I ask is there are two type of coolant temperature sensors for the 1967 442. One is a flat disk type (like if you had the Rally Pack) and one that is single prong (if you have a warning light). I am assuming if you want to want to use coolant gauge you need to use the flat top type.
The oil pressure sensor I have now is for a warning light - I am assuming that would be okay?
You will need to use the sensors that come with the aftermarket gauges or that the aftermarket manufacturer suggests. The original GM senders will not work with aftermarket gauges.
Thank you Fun71 and Loaded - makes sense! When I looked up the Bosch tri gauge (battery, oil, and temp) and I did not see that they came with sending units. Will need to look closer.
