Over heating issues!! 02-03 Pathfinder 3.5L Need help desperately

[JJsTruths]

I have a 2002 Pathfinder with evidently a 03’ 3.5L engine. The stupid “water control valve” hose busted and caused it to overheat. Of course it got hot enough to warp the heads, at first attempt I just block sanded the heads trying to save some $ and they seemed pretty flat. Bought s*** head gaskets and the driver side never held and blew, took it apart 2nd time got a good 3layer felpro gasket and had that head machined this time (thought my guy retired which is why I sanded them) put it back together, did a compression test and all was good. Fired it up and each time it hits about 45mins and wants to over heat. Then passenger side blows. Take it apart a 3rd time, get a good felpro for it and machined. Get it all back together and the damn thing is still wanting to overheat! Brand new water control valve, new water pump, new radiator, new timing chain set, new head bolts, everything from block up is new even injectors. The thermostat came out of my qx4 that’s now a parts vehicle and was only a 1yr old. Changed it back to the old one and same thing, tested both with a torch and temp gun and both open around 170-185 (170 thermostat) 4x I’ve tore this pos apart. Have no clue wtf is going on. Have no heat blowing, bottom radiator hose is cool while top gets hot, seems like just bad thermostats but I don’t understand not having heat even when it’s trying to overheat! It circulates through the bypass if you look at the diagram, so it makes no sense to me. Head gaskets holding good now, no pucking from the radiator at all this time.Also have 2 new temp sensors in it. I’m about to set this pos on fire!! Please someone tell me something here! Has me dumb founded! I’m about to take this 170f thermostat out all together but it’s a mountain ride and daily so need my heat, esp during hunting season. Any help is much appreciated and sorry for the novel! Just at my wits end on this thing. If anyone has did head gaskets on one you know how much of a pain in the a** it is! Now imagine doing it 3x!!

[JJsTruths]

I say 4x cause I took it down to just the water control valve the 1st time and replaced the hose and hoped it was all that happened cause as soon as I seen it getting hot I shut it off. Didn’t think it even got hot enough, long enough to do any damage. In fact the gaskets was fine, just warped the head enough to leak. It’s already been off the rd for like 3months now over waiting for parts and weather.

[VStar650CL]

Is your lower hose new? It's not uncommon for old hoses to delaminate and collapse on the inside with suction applied (which is what you have at the lower with the 'stat open). If you have no heat then it's also likely you still have air in the system someplace. The poor man's bleeding procedure works pretty well on R51's, put a fill bucket on the radiator, park on a steep uphill, and run the engine at about 4000 RPM for 2~3 minutes. Lastly, is your fan clutch any good? No radiator can radiate much without airflow.

[JJsTruths]

It has a burp tube above the plenum that I let burp. I have been suspecting that fan clutch though. Fan spins good but who knows. As far as the lower hose it’s not new but it’s fine.

[VStar650CL]

Fan clutches are easy to check. They should spin freely when cold. Then hit the bimetal with a torch or heat gun, resistance should increase a lot. If there's little or no increase in resistance then the clutch is leaked out.

[mdmellott]

... 2 new temp sensors in it...

A couple more things to test: Those two temp sensors are the ECT sensor on the block and the other sensor outputs to the instrument cluster gauge. Located on the same coolant pipe as the bleed port for removing air from this upper coolant pipe, air trapped there will make your gauge read hotter than the coolant. The ECT sensor can only be read with a scan tool and the two sensors should be reading relatively the same. If the other sensor is reading an overheated condition but the ECT sensor is not, there is likely air trapped in that upper coolant piping. If the sensor temps are relatively the same, the fan clutch is a good place to start for a quick check to see if it is functioning properly. Another possibility is an exhaust gas leak into the cooling system. This too is an easy thing to check, using a chemical test kit available from most auto parts stores.

[JJsTruths]

Well after working on it all day today. I removed the heater core lines and made sure the heater core could get air through it, then removed the burp plug and put a pressure checker on radiator to push everything out of it. Still wanted to run hot. So I said F it and removed the thermostat and physically pulled it out of the housing and reinstalled it. Even tested both thermostats I do have and both open with heat, but I did notice that both these chit motorad thermostats open kinda crooked, then kinda shift over in order to seat. So I just took it out of the housing completely and put it back together and now it’s doing great! Ran it for over a hr 2 different times and never got over a 1/3rd of the gage. The only theory I can come up with is since now it’s all flowing so well due to new pump, chain and all, if you look at the cooling diagram, the only thing that puts heat on that thermostat is the 2 small bypass hoses. So then I look at a factory thermostat and they have a lil built on heat shield that slows the block coolant intake hose down. So heat and coolant will stay around the thermostat alil longer in order to open it. If the thermostat never opens then the system just equalizes and the coolant can’t move anywhere. Still doesn’t make sense why the heater core wouldn’t burn u out of the vehicle. But that has got to have something to do with it. The heater works decent enough for me as is. May just leave the thermostat out. But do NOT buy these chit autoparts store thermostats is my opinion on it. Or at least make sure it has the shield on it. Now I have a vacuum whistle that started all of a sudden under the plenum. Prob from taking it off and on 5x with a new gasket and done smashed it flat. I can deal with that, as long as it’s in time, no cams or valves making noise, and FINALLY not over heating. These dam things are a nightmare to work on! Nissan needs azzs whooped for making this engine lol.

[VStar650CL]

If you think axial VQ's are a PITA to work on, you should try one crammed sideways into an Altima. Or for that matter, try repairing almost anything on a Juke.

[JJsTruths]

Lol no thank ya! Idk how the hell they can get one sideways. The passenger side header and coolant manifold is ridiculous on a rear wheel drive. Couldn’t imagine it shoved up against a firewall. But you could actually get to the coolant manifold on the back alot easier, wouldn’t have to jack the back of the engine up and unbolt the transmission mount to take it off.