I wanted to know which pressure on the radiator caps others use on their 3.9 6cyl Dakota..I'm noticing with a 20lb -the reservoir looses fluid often but it's full under the cap..an with a 18lb the resivoir stays normal but at the cap there's loss of fluid.
......
Both are new caps ...An it's been burped
​​​​​​​Thanks.


​​​​​​Thanks

 

Shouldn't be losing fluid with either cap..... Is the 18 pound cap leaking?

 

Not that I can see .I had ordered,an installed, a new part that joins the 2 hoses with the 1 new cap that all came together w the 18lb cap on it. ..the 20lb is new too an has a release on it, I think it's a auto zone one

...maybe additional air is still there ,but if so I'd think the stant would not show full as I remove cap.
I did a combustion test also(I was curious )-an it's fine .all blue .

 

Rent a pressure tester and test it. Are you bleeding with the front up high? I usually jack my front end up all the way. The system should take care of the rest of air anyway. It self bleeds as the engine heats up and cools. That neck looks like the one on my 4.7.

 

Yes,I raised the front as burping the system, even to the point the level overfilled the funnel .
I will put a different pressure tester on it.The last one was making a spewing sound where that tester
​​​cap meets the new filler neck piece...
Which do you use the 18lb or 20lb cap?

 

My cap is 21 PSI. Yeah, you need an airtight seal and once you pump it up, it should hold the pressure steady for X amount of minutes (google this). If the test cap is sealed good and the needle drops too fast, then you have a leak. Best to do with some fresh cardboard underneath and in a quiet garage if you have access. It took me a few tries using one before I struggled and bit with the correct fitment for the tester too. Finally figured out that I didn't need the adapter portion. Some info and pics in this thread... https://dodgeforum.com/forum/2nd-gen...loss-4-7l.html

Do one of those VIN searches on a Mopar site for the cap and see if you it tells you the PSI there. If it doesn't, google the part number from there, then click on "images" to view all pics.

 

I got a different tester an at the neck it's holding good there ..Oddly both new caps are showing a slow slow leak..the 18 an the 20 ..I'm gonna try another new cap an test it It's odd for both to show leaks ..would you go 18 or 20 ? An would you go with the one that has the release or are they more prone to leak?


It slowly lowered no matter if at 18 or 16 or 20

 

I looked up your cap. It's part # 52029960AB and it's 21 psi. Honestly, I doubt the cap is your real problem, since you've changed caps and neck.
The system will lose pressure over time. How fast is allowable, is the thing. If you lose pressure faster than 10-15 minutes, you probably have a leak. Pump it, wait 10 min or so, get under and look for leaks.

 

You know what I tried..In store on 4 caps- new -not 1 held continued pressure !
Of course it took ,what 50 seconds ,but slowly dropped on pressure - !
An only those same 2 brands 20lb were the in stock ..yes very weird .It's possible that middle, cap adapter piece, on the test kit has a extreme small leak too but rare.
I got a Murry 20lb without the release .
Do those pressure testers loose air easily when it's connected on the direct cap test w adapter?
When I did it on the new filler neck ,normal level of water ,it stayed on the 18 I pumped it to.

Do the tiny tiny tiny bubbles ,that may not have got burped out, slowly get released from a long drive? I went 100 miles on it a few days ago ..I can try a reburp too .I'll recheck hoses also.


Interesting that I need a 21 lb an stores don't carry them ..I guess staying w 20 is ok then?.


Thanks

UPDATE...I burped it more an got bubbles out ...I think ur right on a small very very slow leak...after turning off engine cap has been off a long time ,an reservoir hose disconnected an that opening plugged just as burping ..I watched the level slooooowly go down a lot at opening ..added more up to top ..it went down off an on over 2 hours it kept slowly lowering even when cool an it's dry at the hose connections ...I know water expands an contracts but this is far too much lowering after letting it cool..


Other than in an out hoses at radiator,in an out hoses at water pump ,the 2 at the top where thermostat is ( I bypassed heater core) where else should I be looking? ..I have a new plug in at the radiator an it's dry there an along the bottom .
These type leaks are a pain to find !

Thanks

 

I bought a used 2002 dodge Dakota 3.9v6 2wd automatic. Runs good, but not near he power my old chevy 4.3 had. I replaced the radiator/hose cap with a 18lb. The old cap didnt hold any pressure but it never ran hot.

After replacing the cap I got a water leak at the back of the engine. It turned out to be the freeze plug on the passenger side head near the firewall. Tiny hole rusted in it. 210,000 miles on the motor. I paid 850.00 for the truck. I have the head off waiting on parts. If it had ben a freeze plug on the block between the tranny I'd probably replaced the 3.9 with a 5.9, but it serves my purpose. Looks pretty good for a 2002.

Whoever had it didn't take care of the coolant. At least there is no ridge at the top of the cylinders. so maybe he changed the oil.