Howdy there folks,

My P38 has always liked to show signs of over-pressurizing in the cooling system. It had fat top hoses when I bought it, the previous owner had also recently replaced the radiator, I have since gone through another radiator and now my current radiator is leaking.
It has had various hoses and pipes replaced, as they leaked, and now it seems the radiator is the weak point.

I've done a couple of sniff tests and they don't seem to even show a hint of a blown head gasket.

I always drive with my OBD reader on and it never overheats. (Except for one time over a year ago when the coolant boiled over, I replaced viscous fan coupling, rad fan, radiator, thermostat, expansion tank + cap- it hasn't overheated since).

The day after driving, when I open the expansion cap, a lot of pressure is released.

I've also noticed in this latest leaking episode, that my coolant was extremely low, then when I turned the car on, it returned nearly to full. Not sure if airlock?

I'm a bit lost on what to try since the sniff test returned negative.

2001 P38 4.0L petrol

Is the cabin heater hit?? Have you back flushed it ? Which engine petrol or derv ?

biketeacherdave said:

Is the cabin heater hit?? Have you back flushed it ? Which engine petrol or derv ?

Click to expand...

Yeah the heater seems okay. This latest leaking has coincided with winter here in Australia so I have had the heater on recently.
I have not back flushed anything!
aaaaand it's a 2001 4.0L petrol. I keep those details in my signature

Well I'm going to say do another sniff test, when the car is at least 90c

Also, check the small hoses are all clear, blow through them all. Check the throttle body heater isn't blocked.
Are you following the book when you bleed it? If you hold 2000rpm can you see coolant return visa the filler cap from the bleed pipe?

Fit an aluminum rad, that stops the week spot there. It'll be close to the time to replace all the rubber hoses after nearly 24yr.
I would try a coolant cleaner in the system as well to reduce any build up of crap on the block, head and heater core. This could go some way to improve things.
My diesel is programmed and gets a bit warmer quicker so after it went through rads every two years and nearly blinded me with the last one I opted for the all alu rad.
We can't actually see your model in your signature kiddo

If there's more than 'slight' pressure when the system has been left overnight, then it has to be exhaust gas in the coolant.
If you have a blockage that causes localised overheating (excess pressure) then the pressure will go away as the block cools down

Definitely flush the system through. Have you tested the thermostat & inspected the water pump ? No point in keep changing radiators until the entire system is checked.

Judging by the amount of posts & threads on cooling system, the Thor more often gets airlocks whilst filling than Gems. As said above blow throught the bleed hose first. Personally I use a vacuum pump on the bleed hose to ensure all air comes out as the coolant goes in.

Also what brand of radiator are you using ?

pwood999 said:

Definitely flush the system through. Have you tested the thermostat & inspected the water pump ? No point in keep changing radiators until the entire system is checked.

Judging by the amount of posts & threads on cooling system, the Thor more often gets airlocks whilst filling than Gems. As said above blow throught the bleed hose first. Personally I use a vacuum pump on the bleed hose to ensure all air comes out as the coolant goes in.

Also what brand of radiator are you using ?

Click to expand...

The only time i got an air lock on the Thor 4.0 was if i part drained the system and tried to refill. No amount of burping etc would sort it out and much easier just to drain fully and start again.
Making sure the bleed return pipe is clear was key, along with running up to at least 90c with the cap of then letting it cool for an hour or 2, still with the cap off
(I got lots of airlocks with the knackered engine)

I always remove the overflow hose from the radiator and keep adding coolant to the reservoir tank with engine running until I see a steady stream of coolant coming out of the overflow nipple. Reconnect hose and add coolant as necessary and then let car cool down fully. Top off coolant tank. Only time I have had a problem is when I swapped in a radiator I thought was newer but the turned out to have a blockage.

kermit_rr said:

Well I'm going to say do another sniff test, when the car is at least 90c

Click to expand...

The test I performed yesterday had the car running at 92-94 for around 10 minutes

kermit_rr said:

Also, check the small hoses are all clear, blow through them all. Check the throttle body heater isn't blocked.
Are you following the book when you bleed it? If you hold 2000rpm can you see coolant return visa the filler cap from the bleed pipe?

Click to expand...

I must have read every forum post ever about how to bleed the thing, I normally just ensure the little hose from the rad to the expansion tank is clear by blowing through it and run the engine with the drivers side raised. The top hose squeezing trick normally makes an appearance also.
There is definitely coolant flowing from the filler cap bleed pipe, but it's not that strong, I'll check it today at 2k RPM

Mark Piercy said:

Fit an aluminum rad, that stops the week spot there. It'll be close to the time to replace all the rubber hoses after nearly 24yr.
I would try a coolant cleaner in the system as well to reduce any build up of crap on the block, head and heater core. This could go some way to improve things.
My diesel is programmed and gets a bit warmer quicker so after it went through rads every two years and nearly blinded me with the last one I opted for the all alu rad.
We can't actually see your model in your signature kiddoView attachment 320166

Click to expand...

Haha awkward... you're right, it does indeed not show when on mobile. In my defense, it can be seen on desktop, under my posts.

I looked high and low for a full alu rad here in Australia, but didn't have much luck. I got mine from a shop in Sydney, the bloke there said they used to stock alu rads for the P38 but had more issues with them than the plastic ones.

kermit_rr said:

If there's more than 'slight' pressure when the system has been left overnight, then it has to be exhaust gas in the coolant.
If you have a blockage that causes localised overheating (excess pressure) then the pressure will go away as the block cools down

Click to expand...

I'm not really sure how to measure if it is more than 'slight' or not. The cap isn't blowing off the expansion tank when I unscrew it or anything. But it does give a decent hiss for a few seconds as it is being unscrewed.
I left the sniff test device in the expansion tank for 10+ minutes after the car was turned off and found that I would get a couple of bubbles every few seconds, for the entire 10+ minutes. Not sure if that means something. The sniff test solution definitely didn't change colour to indicate exhaust gas, though.

pwood999 said:

Definitely flush the system through. Have you tested the thermostat & inspected the water pump ? No point in keep changing radiators until the entire system is checked.

Judging by the amount of posts & threads on cooling system, the Thor more often gets airlocks whilst filling than Gems. As said above blow throught the bleed hose first. Personally I use a vacuum pump on the bleed hose to ensure all air comes out as the coolant goes in.

Also what brand of radiator are you using ?

Click to expand...

The thermostat is around 1.5 years old or so, I haven't tested it, but presumably it is working as I don't have overheating issues. I haven't inspected the water pump, that could be a problem, I can check the flow at 2k RPM as I said earlier in this post, if that is munted it could point to water pump issue.

I think the rad is just brandless, the place I bought it from is fairly reputable, not sure if that carries any weight as far as P38 rads are concerned. There's a pretty legit place for rads interstate from me, they specialise in equipment for the Simpson Desert 4WD journeys, apparently they have awesome rads, and some people have fit them to their P38s. I might get my wallet out for one of those if I can confirm no head-gasket + other expensive repairs required.

I should also note that I've found another point of leakage; the heater inlet hose, on the heater matrix side



EDIT TO ADD SOME OTHER IMAGES OF THINGS:

So this is the before and after of the gasket test, no difference in colour that I can see. According to the test it should go pretty orange/yellow if its busted.



Here is the coolant flow:


Here's the gasket test in action, did this for 25 minutes.


And this is the gasket test still with some small bubbles after the engine has been turned off for 10 minutes.

Just a pint, isn't the red liquid for diesel engines? The stuff i used was blue and turned yellow. I tested it using a syringe to pull some gas from the tail pipe.
You're supposed to have the tester plugged into the expansion tank while the engine is running, but that's just to make sure you get decent sample

kermit_rr said:

Just a pint, isn't the red liquid for diesel engines? The stuff i used was blue and turned yellow. I tested it using a syringe to pull some gas from the tail pipe.
You're supposed to have the tester plugged into the expansion tank while the engine is running, but that's just to make sure you get decent sample

Click to expand...

The kit just says to run the car longer if it’s a diesel.
I had the tester in the expansion tank for a good 25 while revving on and off. That second video I linked above has that

enjoi said:

The kit just says to run the car longer if it’s a diesel.
I had the tester in the expansion tank for a good 25 while revving on and off. That second video I linked above has that

Click to expand...

Sorry missed that one!
Do you have a link to where you bought the test kit? I'm very surprised it's red

kermit_rr said:

Sorry missed that one!
Do you have a link to where you bought the test kit? I'm very surprised it's red

Click to expand...

kermit_rr said:

Just a pint, isn't the red liquid for diesel engines? The stuff i used was blue and turned yellow. I tested it using a syringe to pull some gas from the tail pipe.
You're supposed to have the tester plugged into the expansion tank while the engine is running, but that's just to make sure you get decent sample

Click to expand...

The kit I have is a blue liquid and will work with either petrol or diesel kerms

enjoi said:

The test I performed yesterday had the car running at 92-94 for around 10 minutes


I must have read every forum post ever about how to bleed the thing, I normally just ensure the little hose from the rad to the expansion tank is clear by blowing through it and run the engine with the drivers side raised. The top hose squeezing trick normally makes an appearance also.
There is definitely coolant flowing from the filler cap bleed pipe, but it's not that strong, I'll check it today at 2k RPM



Haha awkward... you're right, it does indeed not show when on mobile. In my defense, it can be seen on desktop, under my posts.

I looked high and low for a full alu rad here in Australia, but didn't have much luck. I got mine from a shop in Sydney, the bloke there said they used to stock alu rads for the P38 but had more issues with them than the plastic ones.


I'm not really sure how to measure if it is more than 'slight' or not. The cap isn't blowing off the expansion tank when I unscrew it or anything. But it does give a decent hiss for a few seconds as it is being unscrewed.
I left the sniff test device in the expansion tank for 10+ minutes after the car was turned off and found that I would get a couple of bubbles every few seconds, for the entire 10+ minutes. Not sure if that means something. The sniff test solution definitely didn't change colour to indicate exhaust gas, though.


The thermostat is around 1.5 years old or so, I haven't tested it, but presumably it is working as I don't have overheating issues. I haven't inspected the water pump, that could be a problem, I can check the flow at 2k RPM as I said earlier in this post, if that is munted it could point to water pump issue.

I think the rad is just brandless, the place I bought it from is fairly reputable, not sure if that carries any weight as far as P38 rads are concerned. There's a pretty legit place for rads interstate from me, they specialise in equipment for the Simpson Desert 4WD journeys, apparently they have awesome rads, and some people have fit them to their P38s. I might get my wallet out for one of those if I can confirm no head-gasket + other expensive repairs required.

Click to expand...

Get it up to temperature, release the pressure from the cap and see if it keeps repressurising.

enjoi said:

I should also note that I've found another point of leakage; the heater inlet hose, on the heater matrix side
View attachment 320233


EDIT TO ADD SOME OTHER IMAGES OF THINGS:

So this is the before and after of the gasket test, no difference in colour that I can see. According to the test it should go pretty orange/yellow if its busted.
View attachment 320234


Here is the coolant flow:


Here's the gasket test in action, did this for 25 minutes.


And this is the gasket test still with some small bubbles after the engine has been turned off for 10 minutes.

Click to expand...

Get that leaking pipe sorted lad, there shouldn't be any bubbles present in the coolant at all... The source of the air could well be that leaking pipe I hope

Mark Piercy said:

Get that leaking pipe sorted lad, there shouldn't be any bubbles present in the coolant at all... The source of the air could well be that leaking pipe I hope

Click to expand...

What's worse, getting the dash apart to reach the heater matrix, or doing a head gasket?