I have a 1997 Isuzu Hombre that recently seems underpowered.
Also, I hear a “puttering” sound under the hood while driving.
And, most importantly, giant clouds of white smoke come out of exhaust occasionally. It is not constant.
From my research, this could maybe be a blown head gasket, or, coolant is getting into the combustion chamber somehow.
I don’t want to take it apart to discover which it is. Is there any way to diagnose without taking everything apart?
Sure, run a compression test. A blown head gasket can show a low pressure in 2 adjacent cylinders or, since you have coolant blasting out the exhaust, one really dead cylinder. Also, when it runs you may see bubbles in the overflow tank while the engine is running. But jsut based on your description - head gasket! The compression test will confirm it. Be ready to have the head milled as it may no longer be flat. Maybe a valve job, too, on this 21 year old truck.
An engine cooling system pressure test can also be used in conjunction with a compression test.
I think AutoZone rents out both a compression tester and a cooling system tester.
A more backyard method would be to loosen the radiator cap on a stone cold engine. Retighten the cap and start the engine. Wait about 20 seconds and then loosen the cap. If you hear a hiss there’s likely a head gasket problem.
Cheap easy way to see if combustion gases are getting into the coolant. If they are, that’s a blown head gasket.
Look at the plugs first. One is clean the others normal head gasket leak, oil fouled possible piston rings, carbon fouled ignition or fuel problem. Show pics? Maintenance History?