Hey guys:

Scott here, I'm new the site. My baby is a 1995 f150 with a 302 and 97K miles. I'll start out by posting a problem that I have posted at that site:

I have a hissing sound coming from my engine. I examined the engine by manually opening the throttle--the noise sounds like it's coming from the intake manifold area or around the heads somewhere. The noise only happens when it's cold outside AND the engine is cold. Warm engine or warm (above freezing or so) air temp = no hissing. It begins at medium throttle, maybe 2500 rpm or so (no tach; I'm guessing) and continues for a while after you let off the gas.

Info that may/may not help: I have recently cleaned my throttle body. I am losing coolant, but my radiator leaks profusely (fixing soon...)--there is no coolant in the tailpipes, though. My mpg has remained fairly constant, 16.5 mpg, but this is highway driving--i.e. warm engine driving, when the hissing isn't there anyways. Slightly less accelleration in 5th up mountains at 70mph. Not burning oil, no oil on plugs. It's not the fan clutch. A/C works fine. Idle is smooth. Engine temp is normal.

Any guesses? I am thinking (hoping) maybe the EGR tube is the culprit? I was first guessing right side exhaust manifold, but it really doesn't sound like it's coming from there. I was also thinking maybe it's the intake manifold gasket(s). Has anybody had problems with the above things?

Well, sorry for such a long post but I am stumped. I will probably replace the EGR tube anyways tomorrow, but I appreciate any input that you guys can give me.

later

scott

 

Check for intake or vacuum leaks . The Egr tube at idle doesnt have any exhaust moving thru it so there will be no noise from it so Id say replacing it isnt going to fix the noise problem . Since you have an aluminum intake it may be that the upper intake gasket is leaking . Aluminum expands a lot more than cast iron when it heats up . Cold Engine = Intake Leak , Once the engine & intake warms the aluminum expands enough to seal off the leak . Did you remove the throttle body when you cleaned it ?

 

Thanks for the response.

The hissing does not occur at idle. Only when the throttle is open half to all the way. I did not take the TB off when I cleaned it; it actually wasn't very diry, just a small coating of oil behind the butterfly.

Is my lower intake manifold cast iron? What I am fearing is that the leak is coming from the gasket between the lower manifold and engine. Are both gaskets made out of that lead/paper material?

Thanks again for the input.

later

scott

 

If it is the mainfold gasket..them you likely would be leaking a little coolant too.

My 1988 f150 351 windosr engine has a gasket leak...drips a little behind the engine near the firewall

Cost to repalce 300.00 at FORD.
10.oo gasket

Must remove throttle body and intakle maniofld