2011 Navara D40 cooling system gremlins

[surfalia]

Apparently my wife's Navara overheated again. Last time it was supposedñy due to a leak in the radiator. With a new radiator she was back on the road. The mechanic suggested replacing the radiator cap but said he didn't find one so the old one is what is in there.
The truck interior at the floor has been hot ever since...like the heater is on and maybe it is because the dash had been taken apart to replace the heater fan sometime ago and it doesn't seem like the climate controls are working like they originally had.
Recently she said it had lost power and appeared to be over heated. The mechanic this time said that a leaky water pump was the cause so now she got a new one as well as a new thermostat, radiator cap and reservoir cap.
It was mentioned that the radiator was cold even though the truck supposedly over heated which seems a bit off to me but I'm not the mechanic.
Now the mechanic says it needs to have the head gasket replaced and the head checked for warpage. I drive the truck for an hour plus to get it home and do some research before committing to have the work done. On my drive Into ok it.and kept my speed under 100kph. The temp guage stayed below the middle and the power was fine. When I got home and turned the truck off I heard some gurgling for a moment and when I opened the hood the engine have any Indications that it was running very hot. The engine compartment just didn't seem to be overly hot.
I spoke with one mechanic and he mentioned the possibility of air lock, but another one checked it out with the radiator cap off while the engine was running and said the bubbing he saw coming up out of the radiator has him believing it does need a head gasket. Yet another mechanic said a compression test would be a good way to determine what might be going on in regards to the head gasket and cylinder head.
The compression test didn't say convince him that there was a blown head gasket as the numbers we're relwtively the same running 18 o 20 bar/ 280-300psi. The numbers don't seem very high but there isn't a big difference between any of the cylinders.
Does anyone agree with the airlock theory? It's won't cost me anything to try bleeding the air and the mechanic is planning to park the running truck facing uphill on a short and steep road with the radiator cap off and a 2 liter water bottle with the bottom cut off and turned upside down set into the radiator. Sounds like a good plan to me but I wonder what input any of the professional or semi-pro mechnics on the forum have.
Thanks in advance for taking the time out to read all this and for any advice, input and direction you all might have.

 

[Old.Tony]

It could easily be a busted thermostat too.

I'd flush the cooling system, replace the thermostat (they aren't that expensive), put new coolant in and bleed the system.

Compression testing suggests that all cylinders are functioning normally, and it's quite unlikely that each cylinder will develop an identical crack in the head or gasket.

 

[paddyjacka]

Apparently my wife's Navara overheated again. Last time it was supposedñy due to a leak in the radiator. With a new radiator she was back on the road. The mechanic suggested replacing the radiator cap but said he didn't find one so the old one is what is in there.
The truck interior at the floor has been hot ever since...like the heater is on and maybe it is because the dash had been taken apart to replace the heater fan sometime ago and it doesn't seem like the climate controls are working like they originally had.
Recently she said it had lost power and appeared to be over heated. The mechanic this time said that a leaky water pump was the cause so now she got a new one as well as a new thermostat, radiator cap and reservoir cap.
It was mentioned that the radiator was cold even though the truck supposedly over heated which seems a bit off to me but I'm not the mechanic.
Now the mechanic says it needs to have the head gasket replaced and the head checked for warpage. I drive the truck for an hour plus to get it home and do some research before committing to have the work done. On my drive Into ok it.and kept my speed under 100kph. The temp guage stayed below the middle and the power was fine. When I got home and turned the truck off I heard some gurgling for a moment and when I opened the hood the engine have any Indications that it was running very hot. The engine compartment just didn't seem to be overly hot.
I spoke with one mechanic and he mentioned the possibility of air lock, but another one checked it out with the radiator cap off while the engine was running and said the bubbing he saw coming up out of the radiator has him believing it does need a head gasket. Yet another mechanic said a compression test would be a good way to determine what might be going on in regards to the head gasket and cylinder head.
The compression test didn't say convince him that there was a blown head gasket as the numbers we're relwtively the same running 18 o 20 bar/ 280-300psi. The numbers don't seem very high but there isn't a big difference between any of the cylinders.
Does anyone agree with the airlock theory? It's won't cost me anything to try bleeding the air and the mechanic is planning to park the running truck facing uphill on a short and steep road with the radiator cap off and a 2 liter water bottle with the bottom cut off and turned upside down set into the radiator. Sounds like a good plan to me but I wonder what input any of the professional or semi-pro mechnics on the forum have.
Thanks in advance for taking the time out to read all this and for any advice, input and direction you all might have.

This may be caused by a blocked Cat -I had a similar issue some years ago on a petrol 4x4 of a different brand and it ended up being a bad O2 sensor which stuffed the cat. Not saying this is your issue but I had the same with the passenger floor becoming very hot

 

[surfalia]

It could easily be a busted thermostat too.

I'd flush the cooling system, replace the thermostat (they aren't that expensive), put new coolant in and bleed the system.

Compression testing suggests that all cylinders are functioning normally, and it's quite unlikely that each cylinder will develop an identical crack in the head or gasket.

Supposedly the mechanic put a new thermostat in. Can I remove it and run the car without it if nothing else just to see if the antifreeze blowback out the top of the radiator subsides??
In the morning when the truck was cold I could tell there was a lot of pressure in the cooling system when I removed the radiator cap there was a ton of pressure.

 

[Old.Tony]

Some pressure in the cooling system is normal, but excessive amounts indicate something is wrong and it's possibly a head gasket although the compression testing would indicate this isn't the case. An air lock is possible, but you wouldn't expect to see an enormous rise in pressure from it.

I think it might be time to analyse the coolant for escaped exhaust gases, which would definitively answer the question about the integrity of the cylinders.

 

[SwaziWill]

I found a quick way to determine if a head gasket is blown is to take the pressure cap off. Fit it back on then start the motor and rev 2-3 times switch off. Then open the cap. if there is already substantial pressure it indicates head gasket blown. The expansion from warming in that brief period would not build much pressure.