Lots of us have heard of (or seen) Exhaust Gas Temperature gauges. They're often referred to simply as "EGTs." They do what it sounds like they do: monitor the temperature of the exhaust gases exiting the engine.
This might seem a little silly. Why would anyone care what the exhaust temp is? On an engine that's stock or has been modified with "known" components, it probably doesn't matter. Volvo folks are usually able to set up the fuel system well enough that the engine runs well enough that the car drives well enough that we're willing to drive it. Or something. And on a car like this, an EGT probably isn't needed.
But we're not here only to deal with what's needed. We're here to play with toys. Driving an old Volvo as regular transportation is supposed to be fun. I consider mine a toy and generally can't leave well enough alone.
Whether you start playing with alternate fuel systems (DCOE Webers, exotic fuel injection) on a "known quantity" engine, or you've changed displacement and/or cam profile and/or the flow characteristics of the intake/head/exhaust, knowing what the exhaust gas temperatures actually are can help to ensure that the fuel mixture is correct. Loosely stated, if it's too cool, the mix is too rich and if it's too hot, the mix is too lean. Too rich is bad for horsepower and economy. Too lean can blow a hole through a piston, which I'd consider worse. As always, try to err on the side of caution.
Most of the reputable instrument makers (Stewart-Warner, Auto Meter, etc.) offer EGTs in kit form. A kit should include the gauge itself, a temperature probe and the necessary terminals to get everything connected up.
I chose a dual unit made by Westach (www.westach.com); it's basically two gauge displays in one two-inch instrument. After finding a good spot to mount the gauge (which is just like mounting any other gauge), the real fun begins.
For the gauge to be close to accurate (and thus useful), the probe should be exposed to the exhaust gases, close to the head. The Westach instructions state that two to four inches is proper for their probe -- other manufacturers may have different guidelines, so check and follow the instructions carefully.
Also, there are a couple different methods of attaching the probes. What I'll call Style A uses a welded fitting and a threaded probe. This, I think, is the best way to go. If you plan to install a probe in an OE cast iron manifold, though, welding is a little trickier and you may elect to use Style B. Style B probes are held in place with a band clamp (big hose clamp), which seems a little hokey to me.
I ended up with Style B. I'd like to say it's because I can't weld steel to cast iron, but it's actually because I didn't know exactly what I was getting until it arrived and because I really didn't know what I was doing anyway.
First, we mounted the gauge under the dash. Simple enough.
Next, we tried to determine the best place to drill a couple of holes in an otherwise excellent condition stock manifold. I don't know why it pains me to drill holes in old parts that aren't available any more, but it does.
If you're going to use a single gauge, install the probe in the #4 exhaust. That's the one that runs hottest (generally), so as long as the rest of the fuel system is working properly, you can assume that numberss 3, 2 and 1 are cooler than the one you're monitoring (as long as the ignition system is working right, the valves are adjusted right and the fuel system is working consistently across all 4 cylinders).
If you decide to monitor two cylinders, you'll need to use either a dual gauge, or install two EGTs, and you should install the second probe in either #1 or #2. I chose #1 only because it's opposite #4. I don't know if one way is better than the other.
If you're using a band clamp Style B probe, don't drill until you've had a chance to find a place that will allow snug installation without interference from things like the heater tube below the exhaust manifold (ask me how I learned this one...).
These gauges don't require external electrical power, so once the probe is in place, all that's left is to plug it into the wires (there should be two per probe) and then connect the wires up to the gauge. Then start the engine and enjoy watching your exhaust temp gauge rise. Check for exhaust leaks, then take it for a drive.
I've tried to find the "ideal" temp range, but there seems to be some differing information out there. I've heard "you never want it higher than 1500 degrees and never lower than 1200," and I've heard "anything below 1650 is fine." Nobody has offered anything precise just yet.
What I've noticed is that after a cold engine startup, #1 runs warmer than #4 for a little while, then #4 catches up and runs warmer than #1. At idle, temps are close to 900 degrees, and on the highway (regular driving) they're between 1400 and 1500 degrees. I like knowing this, but I'd like even more to know what it means.
The goodies from Westach ran about $160 not including shipping and handling.
As usual, whenever you add anything to your car, be prepared for surprises and execute the installation in a way that it can be easily maintained as well as being aesthetically pleasing.
Drive happy!
