Intake manifold gasket test

[Jimmy9190]

This is for my 2001 Dodge Dakota, with 142,000 miles on it. 3.9 liter V6 and a 5-speed manual. I removed the throttle body yesterday to clean it and while it was off I took a look down into the intake manifold and I can see oil at the back edge where the manifold meets the belly pan below it. It's not a lot of oil, maybe a teaspoon in total, just lying along that edge. On Dodges this usually means the belly pan gasket is blown, but there is usually much more oil present inside the manifold and there are other problems too-pinging, loss of power and MPG and increased oil consumption. My truck runs OK but is kind of gutless, doesn't have the best power it could have, especially when going up hills. I used my vacuum gauge and at idle my engine has a steady 21 inches, every so often it will blip up to 22 or 23. I pulled the PCV and vent hoses off and at idle there is strong vacuum on the PCV hose, no air movement at all on the vent side.

I don't know what to check for next. I think I might have a blown belly pan gasket. I'd like to know if you guys here think the tests I have done so far indicate a bad gasket. I donn't know enough about the diagnostics to be sure. I can do the work and replace it though.

Thanks.

 

[Chris142]

With it running pinch off the PCV valves hose. Remove the oil filler cap and place your hand over the hole. If you feel vacuun then it's getting vacuum from somewhere other than the PCV valve.

 

[motorguy222]

I had a bad pan gasket on a 318 and it didnt have a lot of oil showing either.It was using oil but the leak was probably more than what yours is doing.

I had good vacuum too.

If it is leaking,it will only get worse.

 

[mechtech2]

Residue in intake manifolds is generally from the PCV vapors that condense.
This may be all that is wrong.
This is why I use a catch can on my PCV line to the manifold.
I hope this is all it is!

 

[Jimmy9190]

Thanks for the help. I pulled a good test info and TSB info for the blown pan gasket off of the Internet today and printed it out. It's a test where you first drive the truck to bring the engine to operating temperature. Then you follow these steps:

Disconnect the breather tube from the air hat on top of the throttle body.

Put a vacuum gauge to the end of the hose.

Then you disconnect the PCV and seal off the hose from it to the manifold and seal off the open end of the PCV.

You start the warmed engine and run it at idle for 30 seconds and watch the vacuum gauge, if there is no vacuum in the manifold then the gasket is said to be OK.

The test also says to be sure to not let more than 3 psi build up in the crank case. I'm not sure how to stop that from happening when you bypass the PCV for this test. I wonder if this is a safe test to run.

I'm going to try Chris142's test tomorrow too when I get home from work.

Like I said in my first post here, there is a very slight amount of oil up against the back wall of my intake, where the back of the manifold meets the top side edge of the belly pan. The rest of the pan is OK, with just a light dry dusty coating on it. I tried to get a pic of it but it didn't turn out very good. Truck runs OK, the tune up I did on Saturday helped a lot. It will cruise at 70-72 MPH on the interstate, and I can pass other cars if I need to, it just takes a little while to build up any more speed. I think it could do better, I had a 2000 Dakota with the same engine and an automatic transmission that was hard to keep it under 85 mph on the interstate. My truck does burn a little oil, about 2000 miles into an oci it will be down about half way between add and full on the dip stick. It's not dangerously low at that point but I usually add half a quart to bring it back to full anyway.

Gas mileage is usually right around 17 MPG, sometimes a little better. There is no smoke or odd noises. Truck is still on the slow side going up hills, unless I have a running start. It will climb some long hills here in 5th gear and drop from 60 MPH to between 55 and 60 but never really seem to be lagging.

I wish I knew for sure whether the gasket is blown. I hope to know more tomorrow after doing the vacuum tests. Chris142's test seems to be the easiest and safest. I am not so sure about the other one that can build too much pressure in the crank case.

Thanks for your help and reading this long of a post.

 

[Jimmy9190]

I just did Chris142's test. Had the engine still warm from my drive home from work, idling in the driveway. I took off the oil fill cap, pinched the PCV hose with a set of duckbill needle nose pliers, heard the PCV valve click so I knew the hose was pinched off very well. Several times I put my 3 fingers across the oil fill hole, I didn't feel a bit of vacuum there at all. I put a piece of paper over the oil fill hole and didn't see the paper being sucked in by any vacuum either.

I think the slight bit of oil at the back of the manifold is just from blow-by from the PCV. That's probably why it collected in that area too, the PCV hose port is right above the oil spot, on the side of the manifold. I believe the belly pan gasket is OK.

My truck runs very well for its age. I think any power loss it has is probably normal and consistent for 142K on an 11 year old V6. I get the same and usually better MPG as other guys with the same truck/engine and transmission. I probably over-reacted when I saw that bit of oil in the manifold on Saturday.

I will leave well enough alone as far as my manifold is concerned. I do want to thank all of you who replied here. This is how I learn about how my truck operates and how to check it all out if something may be wrong. Thanks for your help.