Coolant System No Pressure

[GrannyGearGuru]

I have a 2000 Jeep Cherokee sport with 4.0 and I have no pressure in my cooling system, top or bottom hose, even after driving around for 20 min or so, at temp. I have plenty of heat but I am losing a lot of coolant and I believe its because it is boiling out from the lack of pressure. I have searched forums and have done about everything I know to fix this issue. The previous owner had replaced the water pump and hoses so I started with radiator cap replacement. I have put three caps on, did not fix, put another new gates water pump and thermostat on, did not fix. After that I flushed the cooling system and installed a new CSF radiator. Did not fix. I have no signs of a head issue except the coolant loss so I went ahead and replaced the head with a tupy and with MAHLE head gasket, new head bolts, and intake gasket. I refilled the coolant earlier today, waited until the t-stat opened and added about another gallon. Test drove it for around 20 min. Got back home and no pressure still, radiator cap cool, and was able to pull off the cap without any issue. Anyone have any possible suggestions? Also I put a new heater core on around November because I had lost heating but had issues before then.
Thanks

[GrannyGearGuru]

I also did a pressure test up to 15 psi before replacing the head and was good.

[RCP Phx]

Did you do a pressure test on the completed system, did you check all the freeze plugs?

[GrannyGearGuru]

I have not looked at the freeze plugs yet. I put the pressure tester on the radiator cap. My pressure tester is crappy and have to hold it down by hand so could only hold it at pressure for a min or so. Wondering if I didn't give it enough time to leak down.

[JonnyCat63]

Leaking heater core?

[RCP Phx]

You didn't mention any dripping or pooling so I were old recommend cleaning the engine compartment and doing some dye testing.

[GrannyGearGuru]

Heater core is new. Floorboard is not wet and not wet around the inlet/outlet hoses. Today I checked around the freeze plugs and have not seen any sign of leaking on the ones I can see. I let the Jeep idle in the driveway for about 45 min to an hour with cardboard laying below the engine and is still under it a couple hours later and the cardboard is still dry. Figured if the rear freeze plug was leaking it would run down around the inspection plate. I think I am going to buy another pressure tester since mine will only stay on a minute or two at pressure without popping off and hard to get a decent test. That coupled with UV dye. All connections look dry. I've changed everything. Don't know what else to do.

[RCP Phx]

That's bad news, you need to test your oil and do a sniffer test on the radiator!

[GrannyGearGuru]

So got another pressure tester and pressure tested fine. Tried the radiator cap and it would not hold pressure at all. Tried one of the other 3 I purchased and the Gates held pressure. Installed it and all is fine. I believe the original issue was the old radiator had a crack in the filler neck and why this cap didn't work with the old radiator. Also find it weird that a new csf radiator cap didn't work on a new csf radiator

[Woodswanderer]

Originally Posted by GrannyGearGuru

So got another pressure tester and pressure tested fine. Tried the radiator cap and it would not hold pressure at all. Tried one of the other 3 I purchased and the Gates held pressure. Installed it and all is fine. I believe the original issue was the old radiator had a crack in the filler neck and why this cap didn't work with the old radiator. Also find it weird that a new csf radiator cap didn't work on a new csf radiator

The aftermarket caps that come with the radiators are junk. I recently had to replace mine with a Duralast because it wouldnt hold pressure once warm (aluminum 3row ebay radiator). Had a coolant loss but no overheating, it just wouldnt get warm enough to give me heat from the core.

Glad you figured it out 👍🏻


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