Coolant Air Lock

[Pebbles]

Hi all,
I changed my coolant over today as a result of being told I have been running wrong blend. My issue if someone can assist, is that during the process I believe I’ve picked up an air lock. The temperature gauge shows correctly however the coolant discharging from the drain plug is cold. Also there is no pressure under the radiator cap being able to take it off after running for 15 minutes or longer radiator water also cold. This started happening after a couple of flushes and I have been only able to place three litres into the system each time which would indicate that 6 litres remain in the system which seems a bit high. Any thoughts on a remedy please, also is there any air bleed valves in the cooling system on the NP. Before each flush I ran the motor with heater on full as recommended. Don’t know if this has caused an issue. I have to get this sorted as I’m reluctant to drive the vehicle until such time.
Many thanks.

[chippy4x4]

if you have 2 different temperatures in a cooling system you may have a siezed / stuffed thermostat, as the coolant flow is controlled by this. If you take the thermostat out and it looks ok, boil it in a saucepan and it should open when the water gets to boiling point. If it doesn't move then more than likely it is stuffed.

[Pebbles]

Coolant Air Lock

Thanks Chippy. That of course is a real possibility. My only query is that that everything was fine during the first couple of flushes. Seems strange the thermostat should fail all of a sudden. I have obviously done an incorrect flush some how. Are you aware of any bleeder valve on the NP coolant system.

[erad]

Turning the heater on full does nothing to the coolant flow - it goes full bore all the time. If you want hot air in the car, a flap directs incoming air through the heater core, if not, it bypasses it. So setting the heater to full heat does nothing to help clean the cooling system.

The fact that you have 'normal' temperature at one level and cold at the other suggests that the thermostat is closed. If you want to do a proper flush, you should remove the thermostat and then it will allow maximum flow through the CW system.

[Pebbles]

Coolant Air Lock

Hi Erad, thank you for your input. Just wondering if during one of the flushes some gunt may have disabled the thermostat. I’ll take it out and do the test Chippy suggested. Is there any type of silicon that needs to be smeared over the gasket of the thermostat when reinstalling

[Scooby]

What engine?
Are you draining the engine block or just the radiator drain.

[Pebbles]

Scooby, yes just draining the radiator. It’s NP Diesel engine. I’m starting to think it’s the thermostat that has all of sudden failed or may be jammed with some gunk during the flushing. I have performed a number of flushes in an attempt to clean previous coolant out to change to another coolant spec. Hence why I have been running the heater in an attempt to get as much out of system as possible. I’m not confident in any other method of draining.

[Scooby]

On the petrol V6’s if you only drain the radiator! you only get 3 Litres of coolant out.
To fully drain the system you need to remove the engine block drain plugs and the heater hoses where they do the loop under the drivers feet under the floor.
I haven’t drained the NW diesel yet, so I don’t know what the difference is to the petrol engine, but it is on the list of things to do and it looks like it will be a pain with rear A/C.

In your case if you are trying to fully flush due to incompatible coolants, you should be looking at fully drain the system, I am sure the diesel has a block drain plug and the heater hoses are similar, so drop them off and drain them.
You can them flush the system through these hoses also With the garden hose.

[Kingmarz]

To properly flush a NP 3.2DID you have to remove both top and bottom radiator hoses, thermostat and housing, two heater core hoses in engine bay and two heater hoses under drivers foot area and flush all several times and it makes no difference if heater is turned on or not as there is no valves to stop the water flow and like usual Disco is right.
The rear heater core will be the worst as it seems to work like a sieve and if left will transfer it’s payload elsewhere especially after a radiator flush.
I believe there is a coolant air bleed bolt next to the oil filter if needed check the net for pics.
Your thermostat may have a handful of rust and junk built up behind it?

[Pebbles]

Coolant Air Lock

Thank you both Scooby and Kingmarz, very much appreciated. You know the saying “Leave Well Enough Alone”. That’s kind of where I’m at, at the moment. I’ve been running with the Nulon red coolant for a couple of years now, also as recommended. However, a recent conversation with a Nulon technical advisor informed me my coolant should be the green one. The red wouldn’t cause any issues, it’s the chemical balance where the difference is. However, stated my car would have come into the world with the green hence that’s the better option for my vehicle. Just trying to rid of the red to convert to green however, this hill is starting to become a mountain. I’m not sure I want to go through the loops and hoops of disconnecting all the associated water lines and run the risk of getting myself into more trouble, so may have to suffice with more flushes and get as much red out of the system as I can. I now do believe or I hope that my suspected air lock is indeed my thermostat which indicates why I’m only getting cold water out through the radiator drain and no pressure at the radiator cap. ( thermostat not opening and closing properly). I’m pulling the thermostat out this morning for a look and see. Seems strange it was working fine before I started doing the flushes and in particularly after about the third flush which leads to your theory Kingmarz relating to a thermostat blockage. I shall keep you posted.

[chippy4x4]

Just a heads up mate. A normal house hold hose won't flush out a system / clean it out properly. The volume of water coming from a house hose is no where near what the engines water pump volume is. The blockage did not form quickly and and therefore will not come out quickly. You made need to run a flush additive for a period of time so that the blockages get dissolved. Years ago (early 80s) BP made a detergent called Comprox, speaking back then to the BP rep about a radiator blockage in my XB Falcon he said to put a 1/4 of a cup in the radiator and go for a 2 hour drive. Well we went on a trip to Mt Gambier, 4 1/2 hours away. If I sat on 90 kms an hour the car was ok. If I went faster the car heated up. I changed the water and detergent 5 times on the trip there and back. By the time we got home the radiator was spotless and the car would cruise at 110 kms without any problems. I ran 4 lots of rain water through it over a week, which cleared out the soap. I then took an old Mechanic freinds advice and filled the cooling system with rain water and rubber freindly soluable oil. As he pointed out that he had been running that mix in his cars since the early 60s, and that it kept everything lubricated and corrosion free. I tried it with a loaded trailer and there were no problems with cooling. The car was owned by us for another 5 years and the radiator was never changed.

[Scooby]

Hi Pebbles,
How did you go?
Just a couple of things,
No pressure at the cap means you didn’t get it hot enough, a blocked thermostat won’t stop the system from pressurising, it will cause it to overheat.
If you have the heater turned on with the fan going it will act as a radiator and take longer to warm up if just idling .
If the engine is not warm enough to open the thermostat the radiator coolant will be cold and due to the plumbing the hot coolant in the block won’t drain out.
The temperature gauge is fairly inaccurate so it moves up quick then has a big dead spot in the middle before it rises when it is overheating. It is not linear to temperature.
Can the red and green coolants be mixed what did the tech say?
Do you need to use a flushing agent or will water be good enough.
If you can tackle a thermostat them removing a few more hoses won’t be hard.
The heater hoses under the drivers feet are the lowest point so that is why it is good to remove them.
If you have the thermostat out and the heater hoses off you should be able to flush all of the red out with out having to run the engine, although I would flush with hose, then put it back together fill with water and go for a drive then drop it all again to be sure.
Hope this isn’t too late to help.

[Kingmarz]

Hi Pebbles,
How did you go?
Just a couple of things,
No pressure at the cap means you didn’t get it hot enough, a blocked thermostat won’t stop the system from pressurising, it will cause it to overheat.
If you have the heater turned on with the fan going it will act as a radiator and take longer to warm up if just idling .
If the engine is not warm enough to open the thermostat the radiator coolant will be cold and due to the plumbing the hot coolant in the block won’t drain out.
The temperature gauge is fairly inaccurate so it moves up quick then has a big dead spot in the middle before it rises when it is overheating. It is not linear to temperature.
Can the red and green coolants be mixed what did the tech say?
Do you need to use a flushing agent or will water be good enough.
If you can tackle a thermostat them removing a few more hoses won’t be hard.
The heater hoses under the drivers feet are the lowest point so that is why it is good to remove them.
If you have the thermostat out and the heater hoses off you should be able to flush all of the red out with out having to run the engine, although I would flush with hose, then put it back together fill with water and go for a drive then drop it all again to be sure.
Hope this isn’t too late to help.

Darn right about the factory temperature gauge! It’s FAKE!
Mine goes to just below halfway at about 45 degrees according to my aftermarket one (true temp) and never moves even when pushing hard up hill with a load and true temperature showing 98 degrees the factory one still just below halfway.

WARNING
If anyone see’s higher than normal temperature suddenly on their factory Pajero temperature gauge act immediately cos I’m afraid that if it hits the red it might be too late.
Especially the 2.8 4M40 head cracker

[Pebbles]

Coolant Air Lock

Hi guys, thank you again for your input.
Update: Purchased and installed a new thermostat. On examination of the old one, found no blockage and upon water test, was operating perfectly. Not bad for 16 years. I lost count of how many flushes I conducted, still wasn’t getting all of the red coolant out. More importantly I still wasn’t getting pressure through the radiator cap. Cap and drain coolant still cold. The top radiator hose to the right of the radiator was hot. The hose slightly below and to the right of it was cold. The bottom radiator left hand side of the engine block was also cold to touch. According to my temp gauge I was at operating temp and yes I agree that this gauge may be all show as mine too, registers just below the halfway mark where it seems to sit regardless. Very important piece of equipment in a vehicle, you want it to be working right. I persevered with the idling and heater/ fan speed on full. Utube and other sources of information stated that this was the correct method in achieving a correct flush. I feel at times that it is information overload, particularly when I really don’t know what I’m doing. I found the one (I think there’s only one) bleeder valve on the thermostat housing. Bled it a few times( engine off/engine running at temp). Even tried unsuccessfully removing the bleeder valve and pouring water in. Didn’t have a funnel small enough. Anyway the end result was I took it to a radiator specialist who performed the flush. As usual as they do at these places, I was informed that the radiator needed replacing. Under normal circumstances I would have ignored this advice. Un be known to them though, I was going to do this myself anyway. The difference in price however, including the full flush in them doing it and me buying the radiator and doing it myself was around $100. So I figured it was a no brainer. The results: The temp gauge still sits where it was before commencement of work. The moral of the story, there may not have been a problem in the first place (all in my head). If I had not acted on information received from the Nulon tech, I wouldn’t have been in this situation regarding the coolant flush. Anyway I now have the right colored coolant, no air locks, new thermostat and a new fan clutch. The one remaining piece is the water pump which I hope will keep going for a while yet. The Nulon rep stated that there is a difference in the chemical formula between the red and green and it all equates to how it attaches itself to the surface components. He also stated that the two could be mixed however not recommended. One thing in attempting all of this yourself, you learn a lot in how things work on your vehicle. Again , thank you gentlemen, it is always good to get others input who have experienced similar problems on the same vehicle👍

[Pebbles]

Coolant Air Lock

PS: Nulon guy did suggest investing in a refractrometer to measure the concentration of coolant. Stated that 70% of vehicles would be running around with less than the desired concentration level. I purchased one on EBay for $25. Take care.