On my 84 Duke I was having a great country twisties drive today, going about an hour with multiple stops to check on the engine and other vitals, all good.
But near (-at) the end of the drive, I had a severe loss in power, felt like it was misfiring or chugging, and shortly after it started overheating to just before the red- then I heard some loud bangs and I quickly pulled over and shut it off.
Checked the frunk and there was coolant all over the radiator, lid, headlights, etc....... but no burst coolant pipes and the expansion tank was reading exactly correctly full, and I heard some loud gurglings shortly after that stopped quickly.
At this time also some smoke was coming from the rear decklid- checked it and looked like it was coming from the rear of the valve cover near the exhaust manifold.
Got a ride and came back about 30 mins later with a tow but it started right up and went a few miles speedily without any drama besides a coolant temp spike that settled down.
I'm very confused... what could've caused this?

[This message has been edited by 842m4SE (edited 01-09-2022).]

No Obvious Leaks...

Cap maybe is bad.
See my Cave, Radiator Caps

Find or get tested for exhaust in coolant.
Test uses a liquid that change color when true.
When True then have engine problems... bad head gasket to a lot worse.

See my Cave, Do You Recall?
If is true 84 engine then can be "early signs" borked block etc. and Why many 84 had engine replace under warranty or recall jobs.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

My guess. Blown head gasket. Do coolant check as described by theocre or do a pressure test. If OK replace the radiator cap but my money is on the head gasket. If it is the head gasket you can sometimes fix it with a block sealer but the process to seal the leak using this method can be critical. You must do it without the thermostat in place.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

84 and other years for L4 w/ "bad Head Gaskets" can have bad Head Bolt(s) causing this and any sealer fix won't work.
GM put out TSB for just this problem because #2 H-bolt, E-side between cyl 2 & 3, are known to fail either weak or break.

So when fix, need a Head "Set" and new H-bolt set just for this reason.
Can get a head set/kit of new caskets but better to spend money to get best Permatex intake and valve cover gaskets or expect leaks w/ them days to months later.

Could also have leaking coolant into the intake through the intake manifold gasket/cracked manifold. That may cause surging/bucking too. If you're wondering where all that coolant came from in the frunk your overflow tank pretty surely overfilled and you spilled coolant everywhere in those turns through that cap which is basically an umbrella.

I have an 85 SE V6; I had a problem with overheating- caused by a new water pump that had a plastic impeller that would spin loosely on the metal shaft. At one point it would start overheating- I would pull over and check things, and see that the overflow tank had..."Over-flowed"...But even when I checked it quickly, the water level would be low. So the sudden boiling and overflow would happen very quickly- and subside very quickly.

I swapped in a METAL-impeller pump and stopped having problems. By the way, I was able to drive her home simply by removing the thermostat so that the water could flow freely and there was not much drag on that stupid plastic impeller...But be very careful removing the cap because if it is hot and under pressure......It can get you (I actually carry gloves for working on the car, etc)