I had a 1988 with the same motor as yours. Due to old age and not mileage, you may have an issue with the
intake manifold gaskets starting to leak. They are comprised of hard plastic with rubber sealing rings overmolded onto them. Over time the hard plastic will shrink and creep and the rubber takes a set as well.
My
intake gaskets made it about 20 years and 212K miles when I noticed a small amount of coolant leaking out the end of the manifold.
And as the poster above has stated, if it's a small leak onto a hot motor, you'll smell it before you see it as the coolant will evaporate fairly quickly.
With the engine cold, pressurize the system with a coolant test gauge and carefully check everywhere for leaks. I'd also look carefully around the water pump in the following places: 1) above where the bypass hose goes into the
intake manifold (it's hard to see, it's underneath the alternator which is easily removed); 2) below the water pump, where the weep hole is, your water pump shaft seal could easily be seeping; 3) at the back where the two heater hoses connect to the steel pipes, your pipes may have a pinhole leak from corrosion if the coolant has never been changed, and also where the pipes go into the motor, there are O-rings there; and 4) where the lower radiator hose connects to the pump.
Another place to check is for slow leaks at the radiator side tanks.
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Don't want to spend the $ for a coolant pressure tester? Then make your own! Go down to the big box/hardware store and go into the plumbing section and find a T-fitting (PVC is easy to work with) that has an outer diameter that will fit inside of your upper radiator hose. You'll need a second piece of hose the same diameter so you can connect the other side of the fitting to the vehicle. Now get the plugs and pieces on your third port of the fitting to accept either a 1/8" NPT or 1/4" NPT thread. Buy a couple of hose clamps for the setup as well while you're still in plumbing.
Then head on over to the auto parts or air compressor fittings section where you can find a Schrader valve fitting (has either 1/8" or 1/4" NPT male threads on one end, and a standard Schrader valve on the other end, just like your tire
valve stems do). Insert this valve into the third port on the PVC fitting. You can also find these valves at most auto parts stores in the section with all of the tire valve stuff and air compressor couplers.
It helps to drain a bit of the coolant out of the system first, and then install the fitting in the upper hose. Now take a manual tire pump (preferably one with a gauge and a quick-release hose connection, but either is not absolutely necessary), connect it to the Schrader valve port, and pump up the system to between 7-15 psi. If you don't have a gauge, simply pump it up until the hoses are fairly firm.
Then check for leaks as described above. If you have a gauge, you can also monitor the pressure which should remain steady once you reach your desired pressure. Any decrease in pressure indicates a leak somewhere.
The quick-release fitting on the tire pump is handier, as it makes it less likely that you will get coolant blowback into the tire pump hose when you disconnect it.
You can make your own test setup for under $20, not including the tire pump.
