1987 Chevy Nova the engine runs too cold at +55 mph

check your coolant level. do this while cold, fill the raidator up with 50/50 coolant (green type) and then replace the cap with a new one. then you should have a bottle that says coolant on it and make sure that is half full at least or to the cold mark. then drive it for a couple of days and check the bottle again to see if it is empty. If it is then you possibly have a leak and get it checked out by a pro....

Hi Hmac300 thanks for the reply,
I did replace my radiator cap, top off my coolant and 1/2 full my reservoir. However, it is still running too cold at highway speeds. Too cold meaning the gauge drops to just slightly above the bottom line and the heater blows luke warm. But I do think I must have a small radiator or heater core leak, I say small because after a week of driving I need to add about a quart of coolant. There is no visual loss of fluid in just one days travels, ~ 20 miles.

Would something lodged in my thermostat, blocking it open, cause this?

The thermostat I replaced had a piece of metal blocking it open. I had ruled this out this time because it gets up to a proper temp and holds it in around town driving but cools down after 3-5 miles when you take it up highway speed. Before I replaced the previous thermostat, it never warmed up at all.

it depends what tempature thermostat that you put in the car. If it is ok during the city driving then cooling off on hiwy, then it may be possible that your fan is staying on when it should be off. try no tto add water for two weeks to see if you might be overfilling your radiator tank. If this continues try to check the actual temperature after just stopping and see what it is. you may have a problem with the temp sender or guage itself. You should not have a piece of metal in the thermostat though. The onnly thing that i can think of would be a piece of the water pump or casting breaking off in the engine. Which at this point is nothing to worry about. you might type in your problem under toyota and see what you get there as there may be a problem that i don't know...

yeah, finding that chunk freaked me out. I don't recall what temp thermostat I went with -- but routinely ask for OEM.
I hadn't thought about the fan miss functioning. Can that be tested? if so how?
Theresa

the only thing i could think of is to check the sending unit or sensor for the fan. It woldn't really be the fan's fault as it only works when it gets power. Or if something were shorting it out harness wise to make it run. maybe a relay. But alot of times i think that when you have a problem like this, it's kind of better to check the guage or temp sensor as something may be screwing the sensor up and giving you a flase reading or having a loose or bad ground. A good way to check the ground would be if you hit a bump an dthe guage went up or down then that would be really suspect.

My thought was that if this were just a gauge issue, my heater would still blow hot air no matter what the gauge said--but it doesn't, as the gauge drops, so does the temp of heater air.

I'm going to do that temp. test you suggested and I'm going to pull my thermostat again and see if it too has acquired a blockage, the one I swapped out looked way too new to me and I had though "case solved" for a few days after making that repair. The catch is that I didn't do any highway driving for a few weeks, so don't really know. But I do know that prior, it didn't warm up at all. Anyway, it's back under the hood.

Thanks for your time and thoughts, you've been helpful.

One thing i did forget was to check the radiator. When it is hot oor warm turn teh car off and make sure the fans /fan won't work and feel different areas of the radiator. It shold be the same temp all over. If you feel any cold spots then the radiator is bad as it should be the same temp all over. Other than that i'd would need to look at this to try to solve this problem as it's very hard to diagnose a lot of troble thing like this over the computer.....