My 89 f150 started making this weird sound on the way home from work this morning. I haven't been able to pin it down but it seems to come from the front or top of the engine. it sounds like a pressure cooker release and lasts for a second or so. Only does it on acceleration or steady throttle while maintaining speed. Doesn't happen at idle. It doesn't seem to lose power.
It's an 89 F150, 5.0 EFI, automatic, 4X4.
Any ideas?

 

Ideas anyone? I could really use some help here.

 

the noise could be the pressure release valve on the a/c popping off.does the sound only happen with the a/c on.

 

Hmmmm....now that you mention it, it only happens with the defogger/heater on. but watching the a/c clutch it never seems to dis-engage. (all moving parts always moving) even when the electrical connection disconnected.

 

My truck made the same noise when I blew the gasket on the water outlet after changing the thermostat. If the truck is running any hotter then usual or you see any steam I would definitely look at the cooling system.


Blindlightguy