'93 overheats in mountains

Hey everybody,

I bought a 1993 Chevy Caprice Classic 5.7L about a year ago and it currently has 125,000 miles on it. It runs great, the only issue is some overheating in the mountains on a hot day.

For some background on what has happened and what I've done is this. I live in upstate South Carolina and sometimes take it up the Blue Ridge mountains in North Carolina. The road near Caesars Head get really steep for several miles. On a colder day in the 60's or so, it would make it up fine without getting too hot, but when it would be in the 80's or 90's, the temp mark would get into the orange and hit the white line and I'd be forced to turn around before the top. The coolant would be overflowing into the coolant reservoir.
Besides the mountains in the heat of summer, the car would not get hot as long as we're on a flat road.

One day coming home from work on the highway the temp got hotter than usual. The next day going 5 minutes to the store and back, the temp crept up to the white line. Long story short, I couldn't figure it out and took it to the mechanic. They replaced the fan clutch and thermostat saying the clutch was fairly weak not moving much air.

That instantly fixed the overheating issue around town. I had hoped it would be good in the mountains as well, but it still overheats in the mountains on a hot day. Also if I'm cruising at 90mph or more, the temp creeps up towards the orange.

The coolant temp sensor is new. All the hoses are in great shape, the radiator cap has been replaced and holds pressure. When the cap is off I can see good flow from the water pump, but don't really have anything to compare it too. I had previously tried a radiator flush and the fluid came out like new. Is there anything I could look into next? I would really like to get this problem solved so I can drive up the mountains or be worry free on longer trips.

Thanks! -David

I like the phrase, "cruising at 90mph or more" lol. Im sure one of our more qualified members will chime in here as well, but Im pretty sure what gearing you have plays a major factor. My 2.90 whatevers, really struggle and overheat. My 373's do much better.

What gear are you in and engine RPMs while climbing? Have you tried downshifting a gear?

Are you sure your ignition advance is set properly?

This may show my inexperience, but I'll be honest. The shift lever I'll just keep in overdrive, but the car is usually driving in first or second gear with moderately higher rpm's at times. I'm assuming, maybe incorrectly, putting the shift lever in first or second won't help anything, but let me know if that's wrong. I haven't touched or adjusted the ignition advance since I bought the car since it doesn't overheat in normal driving conditions. Looking up the gear ratio, it looks like there are 2.73 and 3.90 options at least, but mine has the 2.73.

GENDAVIS wrote:

This may show my inexperience, but I'll be honest. The shift lever I'll just keep in overdrive,  but the car is usually driving in first or second gear with moderately higher rpm's at times.  I'm assuming, maybe incorrectly, putting the shift lever in first or second won't help anything,  but let me know if that's wrong.  I haven't touched or adjusted the ignition advance since I bought the car since it doesn't overheat in normal driving conditions.  Looking up the gear ratio,  it looks like there are 2.73 and 3.90 options at least,  but mine has the 2.73.

on a steep grade going up I would shift out of overdrive to drive as if the trans doesn't kick down it's not good on the trans and motor is slogging along at lower RPM. you want the revs up going up a hill for more torque. typically it should shift down on it's own, but to be sure do that.

Also these cars are designed that when driving at highway speed you can run with practically no coolant in them I just had an issue with my WP dying and drove 150 miles home on the interstate and as long as I was going over 40 the temps stayed down, but would shoot up as soon as I stopped for a light when I got off (luckily I live half a mile off the exit).

Have you sprayed a hose through the radiator? It may be clogged up with dirt/debris. Is the fan shroud in good order? I know someone who took theirs off and started having overheating issues until they put a new one on.

I know the radiator is clear of any dirt or debris for sure. The fan shroud has a small crack, but still maintains its shape. Because on the highway, the faster I drive, the hotter it gets, would that be an indication there is something off with the ignition advance? For example on a hot day, driving at 70mph, the temp gauge would be around halfway, at 80mph it would be halfway to the orange mark almost, and at 90 or more, it would creep very close to the orange. The gauge was very precise depending solely on the speed I was at coming back to SC from Florida. Thank you all for your suggestions.

-David

I would say, you have some kind of restriction in your flow then, as the air blowing across the motor even at speed the temp needle shouldn't get past halfway...

I would pull the thermostat and test it in a pot of boiling water. you could have gotten a bad one (it happens). From everything else though it sounds like you covered it. Also, the temp gauge isn't super accurate, you may want to install one that has actual temps on it,

Put in a hotter thermostat,..
When you are climbing the "mountain" manually pull it back to whatever gear it will hold,.
Being a 93 your 700r4 cable dies a ooor job of downshifting unless its a full throttle,.
IF you are climbing the "mountain" at full throttle,. My advice would be to lift off a little, shift back a gear and let the motor rev a little but with out as much throttle input,.
2:73 gears are not ideal for climbing hills.

Just wanted to provide an update 2 years later. I ended up replacing the radiator and now it drives up any mountain with ease staying cool between the quarter and halfway mark on the temperature gauge. The radiator ended up not holding pressure at the outlet and was pretty thin. The new radiator is much thicker and does well. Car still drives like new at 159,000 miles and plan on keeping it going.

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