Intake Manifold Leaking

[milit73]

I have been trying to find out why my car will not idle correctly. It revs good but runs very rough at idle. I started thinking about vaccum. I started spraying around the base of the car (new gasket) all was good, then started around the intake and the car would idle up so that is not good.

Would that also make that car run hotter?

I have never changed out the gasket on this car which is a 1968 383/4 barrel (only Fords). So do I only need a new vally pan gasket? What else would I need to do this? I know get a book which has been a challenge for me for some reason but that is another story. Any help would be great. Thanks Jim

 

[ArtH]

Would it make it run hotter? Possibly as you are running a leaner mixture kind of like adding oxygen to acetylene. I'm not sure about a 383, but my 400 had just a valley pan gasket that ran about $30 IIRC. Have you tried tightening the bolts a little? That might solve the leak. If not, you will have to R&R the intake to try to find out what is causing the leak. Hopefully, the manifold is warped. You can check this with a straight edge across the mating surfaces. Clean really good and check for cracks. When I removed my intake, i cleaned with two cans of oven cleaner. I did it outside and it still burned my sinuses, try to stay up wind of it. The carburetor heat passage that runs from one side to the other was totally clogged with carbon. I had to actually use a drill with a burr to get it out and clear it all up. Nasty.

 

[milit73]

I did not try and tighten the bolts as I thought that might make is worst but its worth a try. I finally have a service manual on the way (third try)

Forgot to mention that the engine had not ran in about 12 years until now.

 

[ArtH]

The engine running hot could be for a variety of reasons including a partially clogged radiator, stuck thermostat, etc. Try solving one problem at a time. The vacuum leak should be pretty easy. Don't go overboard on tightening the intake bolts. I think the specifications for my engine ('77 400 CID) is only 40 lb ft of torque.

 

[67 coronet]

if the motor has not been running for that long,i would pull the intake just to take a look inside.it will solve you leak when you put it back together.as said above,check for any warpage on the intake and head were they bolt together.should just be a valley pan,unless you have an aluminum intake.could have paper backing gaskets on both sides of valley pan.be careful to check for warpage between the intake runners,common spot for problems.

 

[milit73]

Thanks for all the help. This is something I should have did before installing the engine. The other engine ran cool but was tired so the cooling system should be fine.

I will replace the vally pan(it does have an aftermarket intake),thermostat and see what happens.

Other than the Idle the car runs great beside getting a little warm. Hopefully in the next couple of weeks I can get this done and give an update.

 

[Garys1969RR]

You can get a valley pan gasket with the heat cross over blocked. I used one on my 451 and it runs just fine so far. I also removed the thermostat as I have 12 to 1 compression ratio, and soon as it gets too warm it pings at full throttle. This is with 100 octane Sunoco fuel. Maybe for winter and cold weather I will put the thermostat back in.

 

[oldkimmer]

.................u should always run a thermostat........180* is most common for a performance car..........kim.....

 

[Meep-Meep]

I have a hard time correlating an intake air leak with hotter coolant temps. A vacuum leak will definitely cause a rough idle and a lean mixture. I have never had an issue sealing a BB MoPar intake and maybe that's because I never had heads that were excessively milled or some bastard intake. Truth is the valley pan alone with no sealer around the ports will work fine but as said everything must match up well from the beginning.

The intake R&R is so easy you won't believe it. No water and 8 bolts. After you get it apart and clean up the surfaces you should set the intake on without the pan and make sure it fits reasonably well. Not huge gaps between the ports. Eyeball with a mirror and flashlight and estimate the added thickness of the valley pan. If you have huge gaps that the pan won't fill then you will have to go with a thin paper gasket. Normally it's the other way around and adding a gasket will prevent you from getting the bolts started. Use a brush tack sealer around ports and some RTV in the corners and the rail. Also look at your old pan to see how the sealing bead was crushed.

 

[milit73]

Thanks for all of the help and I hope to get to this soon as I am very ready to be driving it as much as possible. Looks like another couple of weeks until I get to work on the car. :angryfire:

Finally have my book so I can find specs now!!!!!!!!!!!!!!!!!