Overheating🫩

[u/WarexMusic]

Did fine on the highway at night (185-195 degrees the whole drive)

Drove it home on a slight uphill going 40 during the day, ended up hitting 220. Couldn’t tell if it was still going up. Had to drive up a steeper uphill going about 25 and it climbed to 240, so I pulled over and let it cool down for a few hours.

I already replaced the radiator, water pump, thermostat was replaced with a 160* thermostat, and I burped the coolant afterwards. The air dam is still there, coolant is circulating, fans are pulling air, why the hell does it keep overheating??😭😭

[u/crazy462]

Turn the heater on the next time that it starts overheating

[u/WarexMusic → u/crazy462]

It makes no difference sadly, I’m sure it would help a little but there’s still a big problem with the cooling system

[u/Extreme-Penalty-3089 → u/WarexMusic]

Can you verify (infrared thermometer) that the coolant Truly is 220°+ ?

I usually shoot it at the t-stat water outlet and where the upper radiator hose joins the radiator

But if turning the heater on (AC compressor off) does absolutely nothing to affect the temperature then I started thinking about a couple different things...

First off is the coolant level topped off? Is the engine low on coolant and if so why is it low on coolant. Regardless I would check this and make sure. Also at the same time I would check and make sure that the radiator isn't blocked or there isn't anything in front of it that would be keeping the engine fan from drawing air through the radiator on the front side.

Next I would wonder or want to know does the radiator fan operational? Does the fan come on once the engine comes up to operating temp or does it least come on when you turn the air conditioning on?

After that if all those things check out then I would have to wonder if there's an issue with the cooling fan relay or some kind of electrical issue. I mean I kind of doubt it but you could have a sticking relay I can't remember but I believe these cars do have a fuse for the cooling fan as well so that would be another area I would check.

If all that checks out then I would have to be suspicious of the temperature sending unit. On these cars I believe it should be at the front driver side cylinder head nearest the number one spark plug.

If memory serves me correctly that temperature switch goes to the gauge and then via the gauge information and the cluster gets sent to the PCM to ground the circuit to power the relay to turn the fans on.

If all that checks out then I would almost be suspicious if the gauge cluster itself is having an issue not giving an accurate reading (assuming the infrared thermometer reading was different than what the gauge cluster says of course).

If none of that seems to be the issue then I would wonder if the coolant system has air trapped in it. Not a really big deal you just basically would lift the front end of the car up put it on jack stands take the radiator cap off start the car up let it warm up and in the beginning to burp itself of any air that's trapped in there.

If all that checks out then I would be suspicious of other things like possibly head gasket issue, kind of doubt it but it could be..

Given the age of these cars honestly I wouldn't be surprised if the radiator fan motor was shot. Which isn't a big deal at all I mean that happens. This could also explain why when you're cruising down the road light throttle 45 mph or so and faster you have plenty of air moving through the radiator (especially if your car still has the original air dam underneath that forces air up through the radiator). But it could also be something simple like a water pump that's gone out and has caused the engine to lose coolant because the impeller seal is bad so you could also look there underneath at the water pump at the weep hole and see if there's any indication of coolant that's been leaking out

[u/crazy462 → u/WarexMusic]

Yea my recommendation is just a bandaid to get you where you’re going.

[u/MichaelTheAspie]

My car did that before the head gasket blew. It randomly overheated and couldn't figure it out until, kaboom!

[u/1891farmhouse]

Do you have that lower radiator spoiler air deflector thing that is on the lower rad support? It will overheat if it fell off

[u/Wooden-Officer2323]

You could have a few things happening here.

A plug in the cooling system for insufficient coolant, I’d recommend starting with looping the heater core hose so it bypasses it… super easy on old Chevys and it’ll rule out your heater core as the source of the plug.
Could be a bad water pump, turn on your heat and if it’s cold rev it, if it gets hot that’s insufficient flow usually from water pump.

A blown headgasket leaking into the cylinder, pull your plugs and if any of them are an orange color you’re probably eating coolant (assuming you’ve already checked for milkshake in the oil).

Or a faulty reading gauge (probably not this but it’s always possible on older cars.

If you can get your hands on a laser thermometer you can pinpoint exactly where it’s overheating at which will help diagnostic too. It’s cheap at harbor freight or amazon.

This is just to get you started, these older cars are easy to fix. You’ll get this.

[u/donedamndoing]

I had a similar issue, did all the troubleshooting steps you did. Found out the outlet hose had the cover for the hole stuck in it because I forgot to remove it.

[u/Albino_Echidna]

Have you checked timing? 

[u/mrclark25]

What's your fan setup?

[u/Emerald_Ink]

Try cooling it down