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Discussion Starter · #1 ·
Hi folks,

I have just spent the last 2 hours combing the forum's cooling issues post, and I couldn't find answers to my problem. Bear with me as this a bit of a long story. Over the last 12 months I have been going through a process of elimination trying to get my cooling issues sorted. My Patrol has been a very reliable vehicle up until about 12 months ago when it started to have cooling issues. This is an early GUIV made August 2004. The old girl has now done 434,000+ klms, and has not given us any bother up until recent times.
The radiator was replaced about 100,000 klms ago, and since the heating issues raised their ugly head 12ish months ago, I have replaced the water pump, thermostat, belt, hoses and fan. Other than a wonky temperature gauge that settles after a thump on the dash, all was going well. Did a recent quick trip up to Broken Hill towing our Tvan and back here to Melbourne over a week (having no issues).After getting back the Patrol started having serious overheating issues any time it had to work. Climbing steep hills for any prolong period as an example. Light driving on flat terrain, the temperature seemed to operate ok. I had it pressure tested, and it held pressure for 30 plus minutes with no variation. Road tested it again, and found significant temperature variation between top and bottom radiator hose. Assuming it may have had a blocked radiator, had the radiator checked and flushed, and the whole system power flushed. Again drives well under no pressure on flat terrain, but once I have driven up a reasonable hill and maintain speed, the temperature gauge just goes straight up to 3/4 and it starts to blow coolant out of the surge tank. As soon as I arrived home, I compared the temperature of the top and bottom radiator hoses, and found the bottom hose to be warmish and the top hose to be hot. I could still hold the top hose for around 5 or so seconds, while there was still a lot of gurgling going on in the system. Engine runs beautifully, no oil in the coolant, no coolant in the oil, and as far I can tell no bubbling in the system at idle with the caps off. So at my wits end.
Sorry for the short novel, but hope it covers question that some may have. Now putting it out there to the brains trust.

John
 

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Y2KGUII ZD Wgn
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Hi folks,

I have just spent the last 2 hours combing the forum's cooling issues post, and I couldn't find answers to my problem. Bear with me as this a bit of a long story. Over the last 12 months I have been going through a process of elimination trying to get my cooling issues sorted. My Patrol has been a very reliable vehicle up until about 12 months ago when it started to have cooling issues. This is an early GUIV made August 2004. The old girl has now done 434,000+ klms, and has not given us any bother up until recent times.
The radiator was replaced about 100,000 klms ago, and since the heating issues raised their ugly head 12ish months ago, I have replaced the water pump, thermostat, belt, hoses and fan. Other than a wonky temperature gauge that settles after a thump on the dash, all was going well. Did a recent quick trip up to Broken Hill towing our Tvan and back here to Melbourne over a week (having no issues).After getting back the Patrol started having serious overheating issues any time it had to work. Climbing steep hills for any prolong period as an example. Light driving on flat terrain, the temperature seemed to operate ok. I had it pressure tested, and it held pressure for 30 plus minutes with no variation. Road tested it again, and found significant temperature variation between top and bottom radiator hose. Assuming it may have had a blocked radiator, had the radiator checked and flushed, and the whole system power flushed. Again drives well under no pressure on flat terrain, but once I have driven up a reasonable hill and maintain speed, the temperature gauge just goes straight up to 3/4 and it starts to blow coolant out of the surge tank. As soon as I arrived home, I compared the temperature of the top and bottom radiator hoses, and found the bottom hose to be warmish and the top hose to be hot. I could still hold the top hose for around 5 or so seconds, while there was still a lot of gurgling going on in the system. Engine runs beautifully, no oil in the coolant, no coolant in the oil, and as far I can tell no bubbling in the system at idle with the caps off. So at my wits end.
Sorry for the short novel, but hope it covers question that some may have. Now putting it out there to the brains trust.

John
Any idea what actual temps you are seeing? Sorry to ask but you are sure the caps went on in the right sequence, seal cap on radiator and pressure cap on the top plastic tank? Are you hearing the gurgling in the lower surge tank? How hot is you auto getting remembering the auto cooling runs through the bottom of the radiator?
 

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have you checked to see if any of the aero components are missing/ damaged . such as airdam , plate that goes from bottom of bullbar to frame at radiator , rubber flaps that separate high pressure wheel well area from low pressure engine bay area and there should a rubber strip underneath the front of the bonnet that stops air going over the top of the radiator . if you have a big lift it may be messing up the airdams operation
 

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nissan patrol guiv
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Discussion Starter · #4 ·
Any idea what actual temps you are seeing? Sorry to ask but you are sure the caps went on in the right sequence, seal cap on radiator and pressure cap on the top plastic tank? Are you hearing the gurgling in the lower surge tank? How hot is you auto getting remembering the auto cooling runs through the bottom of the radiator?
Not sure what the actual temps are. I have the cable to connect to my laptop so will do that. No need to be sorry for asking the question, because at this point no question is a silly question. Caps are in the right location. The gurgling was coming from lower in the system. Transmission temps are good. I have a Redarc transmission temperature sensor and gauge fitted. Thank you for your reply.
 

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Discussion Starter · #5 ·
have you checked to see if any of the aero components are missing/ damaged . such as airdam , plate that goes from bottom of bullbar to frame at radiator , rubber flaps that separate high pressure wheel well area from low pressure engine bay area and there should a rubber strip underneath the front of the bonnet that stops air going over the top of the radiator . if you have a big lift it may be messing up the airdams operation
Thank you for your reply. I have noticed after you asked about missing items around the radiator that the foam between the radiator and bonnet is now missing. The rubber flap on the bonnet is still there. All the other items you have listed are there. There Patrol has only got a 2" lift. The vehicle is only used for touring and not as a weekend warrior type scenario. The last big trip it did was the Simpson in 2019 just before lockdown. All trips before that like flinders Ranges and the Oodnadatta Track in 2018, the vehicle was faultless.
 

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Y2KGUII ZD Wgn
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Not sure what the actual temps are. I have the cable to connect to my laptop so will do that. No need to be sorry for asking the question, because at this point no question is a silly question. Caps are in the right location. The gurgling was coming from lower in the system. Transmission temps are good. I have a Redarc transmission temperature sensor and gauge fitted. Thank you for your reply.
When you say lower in the system, do you mean the lower surge tank with the small yellow cap? Can you hear this bubbling after a drive with engine hot and standing beside said tank?
 

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Discussion Starter · #7 ·
Just took the Patrol for anther short drive, temps stay normal with easy driving. Drove up a reasonably steep long hill, temps stayed normal Then when going back down said hill, the the temperature went straight up to 3/4 then to hot. Blew the surge tank cap off. Stopped the vehicle, no further steam coming from tank. Felt the bottom radiator hose, barely warm. The top radiator hose very hot.
Yesterday took it for the same drive, it got to 3/4 , then settled back down. The hoses do not seem firm enough that the system is being over pressurised. I do not want to start major mechanical work until I have eliminated all other avenues.
 

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Just took the Patrol for anther short drive, temps stay normal with easy driving. Drove up a reasonably steep long hill, temps stayed normal Then when going back down said hill, the the temperature went straight up to 3/4 then to hot. Blew the surge tank cap off. Stopped the vehicle, no further steam coming from tank. Felt the bottom radiator hose, barely warm. The top radiator hose very hot.
Yesterday took it for the same drive, it got to 3/4 , then settled back down. The hoses do not seem firm enough that the system is being over pressurised. I do not want to start major mechanical work until I have eliminated all other avenues.
I don't know if you have the facilities to do it, but I made my own radiator pressure testing unit which makes it easy to pressure test a system overnight, I wrote it up in my build thread HERE so if you can give it a go.
This is concerning it blew the surge tank cap off, if your talking about the small yellow cap then that tank has a breather hole just under the cap, so no pressure should ever be in there.

I hate to even suggest it but I'm concerned there is a head gasket weep between cylinder to one of the small water galleries between the cylinders, hence my suggestion to pressure test overnight and see what happens. This is why I asked if you could hear bubbling from that lower surge tank after a drive.

Just in case you don't know. the top tank holds the pressure, as the coolant expands it pushes some coolant over to that yellow capped tank, when the engine cools what has been pushed over is sucked back into the main system. Get used to checking the level in that lower surge tank every morning before starting engine, it should remain at a constant.
 

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Discussion Starter · #9 ·
It was pressure tested a couple of weeks ago, and held pressure for more than 30-40 minutes with no variation. I am calling the high pressure tank the surge tank because that is what I have seen it called on part supplier sites. I thought the non pressurised tank was called the overflow. So sorry for talking at crossed purposes. It blew the high pressure cap off. We initially thought head gasket, but because of the pressure test, we went searching for other avenues. It still may be the head gasket, that is allowing pressure into the system under heavier work load, but the engine running beautifully even when it is getting hot. Could it be a faulty water pump, even though I have replaced it in recent times? As I have said earlier, I don't want to start spending big money on engine work unless I am certain it is nothing else. I really appreciate you helping me with this issue. Thank you
 

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It was pressure tested a couple of weeks ago, and held pressure for more than 30-40 minutes with no variation. I am calling the high pressure tank the surge tank because that is what I have seen it called on part supplier sites. I thought the non pressurised tank was called the overflow. So sorry for talking at crossed purposes. It blew the high pressure cap off. We initially thought head gasket, but because of the pressure test, we went searching for other avenues. It still may be the head gasket, that is allowing pressure into the system under heavier work load, but the engine running beautifully even when it is getting hot. Could it be a faulty water pump, even though I have replaced it in recent times? As I have said earlier, I don't want to start spending big money on engine work unless I am certain it is nothing else. I really appreciate you helping me with this issue. Thank you
I know what you mean, you need to go through all the steps before taking the plunge on big jobs. OK so pressure tank cap blew off, never heard of that, did it do any damage? When they pressure tested the system did they do it at the pressure tank or at the radiator? Something very strange going on here.
 

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Discussion Starter · #11 ·
Yes the saga continues.
 

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I am calling the high pressure tank the surge tank because that is what I have seen it called on part supplier sites. I thought the non pressurised tank was called the overflow. So sorry for talking at crossed purposes. It blew the high pressure cap off.
Pressure cap should allow excess coolant expansion to pass thru into overflow tank (yellow cap) _ Is the pressure cap functioning properly? Cap should not blow off, if it is functioning correctly? Check "surge" header tank outlet spigot pipe and hose to overflow tank is not blocked _ would expect hose to blow off if blocked

Had a head / hd gasket fail recently and could see air bubbles rising in "pressurised" header tank with cap removed, maybe you could run without pressure cap and see if air bubbles are evident n header tank with warm eng?
 

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i have just read your post no-7 . i probably would not fully discount a faulty head gasket yet but as i have a lot of experiance with various types of heat exchange and pumping systems , what you described seems to be classic intermitant blockage senario . where there is something inside the the cooling system that is moving around ( sometimes in a position to block or partially block a passage or oriffice or sometimes not ) . for me , 9 times out of 10 it would be a part of a broken non return valve . they are mechanical items with wearing parts that sometimes wear to the point of falling apart . the thermostat is a mechanical item with wearing parts also and i would suggest the likley culprit and a good place to start . since your overheating issues started you wrote that the thermostat has been changed . do you know what condition the old one was in -ie; was there any bits missing that might be moving around in the cooling system . in the past i have found rags , nuts and bolts and bits of steel and plastic left in pipes , pumps , heat exchangers and valves , but mostly broken non return valves . i don't know what sort of diagram the workshop manuel has on it , but from it you may be able to tell where the most likley place an object could lodge to start looking .
 

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i have just read your post no-7 . i probably would not fully discount a faulty head gasket yet but as i have a lot of experiance with various types of heat exchange and pumping systems , what you described seems to be classic intermitant blockage senario . where there is something inside the the cooling system that is moving around ( sometimes in a position to block or partially block a passage or oriffice or sometimes not ) . for me , 9 times out of 10 it would be a part of a broken non return valve . they are mechanical items with wearing parts that sometimes wear to the point of falling apart . the thermostat is a mechanical item with wearing parts also and i would suggest the likley culprit and a good place to start . since your overheating issues started you wrote that the thermostat has been changed . do you know what condition the old one was in -ie; was there any bits missing that might be moving around in the cooling system . in the past i have found rags , nuts and bolts and bits of steel and plastic left in pipes , pumps , heat exchangers and valves , but mostly broken non return valves . i don't know what sort of diagram the workshop manuel has on it , but from it you may be able to tell where the most likley place an object could lodge to start looking . just thought i'd add , if it is a partial blockage a pressure test will not tell you anything . but could contribute to blowing the pressure cap off as the car gets hot as the back pressure would add to the increased pressure with higher temperatures especially if the blockage suddenly moves to block the flow more .
 

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not sure if i did this right . i wanted to add to my previous post but i don' think it is clear that i added more to it . is there a better way to go about this ?
 

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not sure if i did this right . i wanted to add to my previous post but i don' think it is clear that i added more to it . is there a better way to go about this ?
Just hit edit to add info to original post and then save.
 

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Discussion Starter · #18 ·
Thank you for your thoughts. I won't be able to do all the checks until later in the week due to work. There are few things I will need to check, based on the comments. I still have the old thermostat, so I can check it. I will also check the high pressure surge tank. I will give an update when I have gone through the items mentioned.
 
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It seems like you've covered all the easier things I can think of. The only other thing I would look at is the pressure cap on the surge tank. If it's not sealing correctly (screwing on properly) or not holding pressure correctly (allowing coolant out at a lower pressure) then the coolant will heat quicker (higher pressure = higher boiling point, lower pressure = lower boiling point resulting in rapid coolant expansion).
If it's not screwing on correctly or securing properly that could explain it blowing off.
Hope you can get to the bottom of it.
 

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I don't know if you have the facilities to do it, but I made my own radiator pressure testing unit which makes it easy to pressure test a system overnight, I wrote it up in my build thread HERE so if you can give it a go.
This is concerning it blew the surge tank cap off, if your talking about the small yellow cap then that tank has a breather hole just under the cap, so no pressure should ever be in there.

I hate to even suggest it but I'm concerned there is a head gasket weep between cylinder to one of the small water galleries between the cylinders, hence my suggestion to pressure test overnight and see what happens. This is why I asked if you could hear bubbling from that lower surge tank after a drive.

Just in case you don't know. the top tank holds the pressure, as the coolant expands it pushes some coolant over to that yellow capped tank, when the engine cools what has been pushed over is sucked back into the main system. Get used to checking the level in that lower surge tank every morning before starting engine, it should remain at a constant.
You clearly have no idea about a sound theory of operation of a propper and working cooling system.

FYI you shouldnt just about ever be running on cap pressure, even though the overflow bottle could be suggesting this is the case.

This is a band aid type item that is in place to make up for a myriad of conditions that can result in static pressure being to high when an engine is placed in a vehicle on a production budget
 
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