The big 2.3E coolant temperature mystery

[Luuk813]

Hi all,

I've asked a couple of "targeted" questions regarding the issue's I'm having with my 2.3E (NG) Cabriolet's cooling system, but I've still not been able to fix the overheating. I hope that someone has enough knowledge on this front to help me out, since it has now been the second summer in a row that I've not been able to enjoy driving the Cabriolet cause of this issue. I am not the most experienced regarding mechanical work, so please keep that in mind.

The problem:

Last year, when I initially bought the car, I took it out on a long drive, and got stranded with an overheating engine (coolant spurging out & around 120c on cluster). After replacing the MFTS and the 2-pin temp sensor above it, I've yet to have it boil over again, but the coolant temps are still really high.
Since I don't got it assured at the moment, I can't take it for a long drive to see if it will eventually start boiling over again, but the temperature will consistently reach 110c after about 20 minutes of just idling (ambient temp just 24c). The fan kicks in on level 1 when the cluster says that the coolant has reached around 100c, but turns of pretty fast again, after only a couple of seconds. Once it has reached 110c, the fan spins for around 30 seconds on level 1, and then turns off again for 30 seconds as well, to constantly repeat this process.

PXL_20230816_184103686[1].jpg

What I've tried so far:

- Replaced MFTS sensor
- Replaced 2-pin temperature sensor on top of coolant flange
- Replaced thermostat
- Cleaning 3 pin radiator fan switch sensor
- Flushed the system (alot of times)
- Tried to see if the first and second speed fan is working by removing the corresponding fuses.
- Put the garden hose on both radiators to see if it's blocked, but both seem to be alright

I've been using pure distilled water since using it is way cheaper then using coolant, because I have had to drain and refill the system alot for testing recently. I hope to only have to fill up the system with coolant once the overheating is actually fixed, or once it'll start freezing of course.

I use this forums recommended method of draining the air out; by lifting the coolant reservoir. It burbles up a lot of air when I let the engine get hot and turn it off; you can really hear a lot of air moving inside the entire system. After a while it stops, but when I run the engine again, it once again burbles up a **** ton of air, like I've not even tried draining it out before. I must have repeated this process for 5 times, but it'll still burble up a lot of air when you do it again.

Things that might be suspicious:

- The auxiliary radiator has been leaking in the past, and is a bit corroded from the outsite, but doesn't appear to be actively leaking:
PXL_20230816_184751716.jpg
- The main radiator has had some side impact in the past, and is a bit bend on the right hand side:
PXL_20230816_184755113.jpg
I've been told that both of these should not cause any major problems, like the once I'm facing. Since my cabriolet is an automatic, and therefor has an oil cooler inside of the main radiator, I can't just go out and buy a replacement.

- The coolant temp/level warning light flashes when the car is in accessory mode, but not when the engine is running for some reason?

Hope anyone is able to help me out with this one, since I'm not sure what's the best thing to do next .

[Tractor Dave]

Have you tested for exhaust gasses in your coolant bottle? Local good garage should be able to check for you with a tester. If they are present, you will need to do the head gasket.

[Luuk813]

The first garage I went to right after having the issue told me that they done some testing, but that it was very unlikely that it would be a blown head gasket. Not really sure anymore if they told me they tested the exhaust gases from the exhaust itself, or if they tested the coolant for exhaust gasses.
Shouldn't there be white smoke forming from the exhaust if the head gasket is the culprit?

[B5NUT]

When was the water pump last changed?

[Tractor Dave]

The first garage I went to right after having the issue told me that they done some testing, but that it was very unlikely that it would be a blown head gasket. Not really sure anymore if they told me they tested the exhaust gases from the exhaust itself, or if they tested the coolant for exhaust gasses.
Shouldn't there be white smoke forming from the exhaust if the head gasket is the culprit?

Not always. Worth checking to eliminate.

[Tractor Dave]

When was the water pump last changed?

Yes, maybe the impeller has broken.

[Tractor Dave]

I once had a 2.8 Granada auto that had a coolant pipe in the radiator. It's probably the worst ever idea to cool your gearbox oil as over time it corrodes and eventually fills your gearbox with water

[Luuk813]

When was the water pump last changed?

I don't have any documentation on when it last got changed, so it might even be the original one! Since changing the water pump seems like quite a big task, is there any way to test the pump without removing it? Is it correct that you have to remove the timing belt when servicing the water pump?

[Luuk813]

I once had a 2.8 Granada auto that had a coolant pipe in the radiator. It's probably the worst ever idea to cool your gearbox oil as over time it corrodes and eventually fills your gearbox with water

I'll make sure to drain the ATF fluid after reading this to make sure there's no water in there. Thanks for the tip!

[Tractor Dave]

Water pump is timing belt driven. When was the belt last changed?. You might just be able to feel the pump impeller through the thermostat housing. Not sure now. Never tried.
You will know if there is water in your gearbox. It will fail immediately

[Tractor Dave]

What is vital with this design is regular anti freeze changes so the inhibitor is working properly. If this hasn't been done, I would recommend changing the radiator.

[Luuk813]

Well, I don't think the coolant got changed alot in the past, since this is how the inside of the thermostat flange looked like after removing it:

PXL_20230816_101058321.jpg

A layer of the brown filth you see can also be found in the rubber coolant lines. I've tried to clean it up as best as I could. Perhaps a chemical flush would help remove it further? I wish I could buy a fitting replacement radiator, but there are no original ones still on sale, neither are there any aftermarket alternatives (OEM number 893121251N).

When I bought the car the original green G11 was however already replaced with the pink G12, so it atleast got it's coolant changed once before in it's lifetime .

I can borrow a thermal camera from my work that I will try to use to see if there's perhaps anything blocking the system. I will also reach out to one of my local garages to ask them to check for exhaust gasses in my coolant, just to (hopefully) eliminate it as a potential problem, like you said.

[John.]

Maybe an idea to use an infra red thermometer to check against your temperature gauge in the car, to see how accurate it is?
Regarding the main radiator, better idea would be to obtain a separate cooler for the gearbox so it's completely separate from the engine coolant, you could then just use an ordinary radiator which should you choose to replace would be easier to source...maybe !?
Not a nice thing to have the temp gauge reading high, hope you get to the bottom of it.

[Luuk813]

I just used my works old school FLIR camera, and might have found something interesting. First off, the temperature gauge is 100% accurate with the temperature of the water that flows by the MFTS, so it's good to know that I can trust that reading. The fan thermo switch in the radiator is also working correctly; the fans turn on at speed one once the water reaches around 95c there, just like the manual says it should.

What is interesting to me however is that the radiator is not heating up evenly. There is a big difference in the temperature on the right hand side, where the dent is. I saw differences of 100c on the right, versus only 55c (!) on the rest of the radiator:

PXL_20230817_160626231.MP.jpg

The picture above shows up how the radiator heats up, just before the fan kicks in. The reservoir on top heats up evenly, but the radiator fins accumulate heat mostly at the right side. Please ignore the hot tube coolant tube on the left, and the cold power steering line on the right (marked with white arrows). I couldn't get them out of the shot. Once I found a CompactFlash reader I'll upload the pictures I made so that you can get a better understanding of what I mean.

Am I correct in thinking that this is at least A problem, even though it might not be the only problem?

[VW-1964]

Have you checked that you don't have an air pocket on the top-side of the thermostat. I also have an NG engine in my 1991 Coupe, and getting the system properly bleed is key. Before finding the write-up somewhere here on the forum, I was having an air pocket causing the thermostat not to open, resulting in the temperature raising. Getting it bleed correctly solved my problems.

Peter