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Zara19

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Discussion starter · #1 ·
Hey! I’m a new d40 owner. Have come across from a 99 petrol prado which I’ve learned to work out, to diesels, which is completely different and I’m hoping you guys could help with investigating a problem.
The new car was brought with an overheating problem. First thing I noticed was a pressurised cap on the radiator which has been changed to a blanking cap, but the problem is that replacing it hasn’t stopped the air bubbles coming through despite bleeding the radiator.
Now I understand they’re notorious for a blown head gasket, but these bubbles aren’t gas related as the chemical test has been done roughly 4 different occasions to check.
I’ve also noticed both inlet and outlet heater core hoses aren’t hot or even warm for that matter, which explains no heat in the cab.
The water in the reservoir is cold to touch but the hose leading to it is warm touch as well as the top of the radiator which seems odd as the reservoir is getting its water from the radiator? Or am I wrong there?
Now I’ve done a radiator flush, it was pulled out and rinsed through with a hose and has a great flow rate.
The heater core was also flushed through with the hose and seems to have a great flow rate to. It’s also not leaking into the cab.
Would this indicate they are functioning? Can they be ruled out as a problem at this point?
The car takes a roughly 5-10 mins to heat up on idle, it’s been taken for a spin (after attempting to bleed air from radiator) and she has not overheated but noticed the indicator started to climb after running at around 85/90 for about 2 minutes and being careful we’ve backed off on speed and she’s immediately gone to normal operating temp.
The symptoms are confusing me, on one hand a mid stuck thermostat could be the reason she takes her time getting to normal operating temp.
If the inlet to the heater core isn’t even warm then I believe the issue to be somewhere before the heater core but after the radiator as it’s hot.
There are no noticeable leaks. The only time she loses coolant is when the reservoir becomes pressurised, having coolant leak from the pressure point (not sure of the name but the nozzle at the top where the lid is) which is caused by air gaining access to the cooling system or being present still but where and why.
Is the valve for the heater core not working and that’s why the heater in and outlet isn’t hot?
She’s been bled a ton, and I don’t want to start replacing everything that doesn’t need replacing in the hopes I’ll find it.
So I guess I’m just looking for potential causes before it becomes heater core replacement and thermostat and maybe temperature sensor then posibile faulty hoses. We all know parts for these beasts aren’t cheap! So what are your thoughts and what is the best way to test them or best symptoms to search for.
Please help me understand how it all works and your general thoughts on what it could be.
Also to note, after having done the last air bleed tonight, there was no sign of bubbles coming up through the reservoir. I’ve yet to take her on a decent drive around the block to find out if it’s fixed anything only because of the symptoms above (heater core hoses and reservoir water was still cold) still being present after bleeding the air. Just makes me a bit worried the problem which causes the temp gauge to climb at a higher speed might still happen and indicating the problem wasn’t located.
Also thankyou to anyone who’s taken the time to read this!
 
Welcome to the forum. Indeed a long post.

Somewhat of a risk to buy a vehicle with a known fault, but it sounds like you know what you doing.

Firstly, the radiator cap should be a blank, the one on the expansion tank is the pressure one.

I am thinking with all the work you have done that the head gasket sounds likely.

What happened to me was the head gasket started leaking just above the alternator, a tiny leak that only lost water when running. It took a pressure test to discover that it was leaking, never a drop of water on the driveway though.

I used Würth leak sealer, that did cure the problem, although the head gasket was changed at a later date.
 
Hello, Zara, welcome.

Seems like you are really getting the chance to know the old D40l!

Yeah, chemically testing for the presence of combustion gases in the coolant, in this case, is only a parameter gathered in order to add to other prospective evidence of head gasket failure. Because it tests negative does not 100% clear the gasket. Besides, I highly doubt anything below about 20 or 30 PPM (Parts Per Million) would be detected with these simple test kits.

I have to agree with Landmannnn, after all you have done, I think the head gasket could still be the biggest suspect.
 
Discussion starter · #5 ·
Welcome to the forum. Indeed a long post.

Somewhat of a risk to buy a vehicle with a known fault, but it sounds like you know what you doing.

Firstly, the radiator cap should be a blank, the one on the expansion tank is the pressure one.

I am thinking with all the work you havdone that the head gasket sounds likely.

What happened to me was the head gasket started leaking just above the alternator, a tiny leak that only lost water when running. It took a pressure test to discover that it was leaking, never a drop of water on the driveway though.

I used Würth leak sealer, that did cure the problem, although the head gasket was changed at a later date.
Thankyou for the suggestion! The fella previously threw in kemiweld which blocked the radiator and is the reason for the mad flush. I’ve also done a radiator pressure test (just waiting on the combustion pressure test) and the pressure did hold. I suspected maybe a leak through a hairline crack in the water gasket which would only show when the car cooled down so to speak but she seems to be a sealed unit? Will let you guys know what the combustion test shows as I’ve been told that’s the only sure sign?
 
I am told Wurth is the only sealant that won't block up the radiator and heater, but not an ideal solution. Have you done just a radiator pressure test or a full system pressure test?

As I said, the normal problem is a water leak from the head gasket, so a combustion test won't find that, but it is a useful test that needs doing.
 
Discussion starter · #7 ·
I am told Wurth is the only sealant that won't block up the radiator and heater, but not an ideal solution. Have you done just a radiator pressure test or a full system pressure test?

As I said, the normal problem is a water leak from the head gasket, so a combustion test won't find that, but it is a useful test that needs doing.
Have done a radiator pressure test through the reservoir cap and she is holding very well. What’s a full system pressure test?
 
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