The Project Pad

Drained coolant and removed radiator. Unfortunately this is necessary with my setup in order to get the t-stat out. Even then it's still messy.


Note the orientation of the brand new thermostat that was in there. Looks good to me. (Wahler thermostat from 034)


New thermostat from Audi dealership vs. the one from 034. it's interesting to me that neither thermostat has a hole, but I guess I haven't had one with this on an AAN yet.


So it doesn't look to me like this has made any change. Which to say the least makes me want to light this car on fire even more than I already had. But i'm convinced that there is something small that is right in front of me that I'm just not seeing that's causing this issue of running a little hot.

Ok Taking a new approach. If anyone has any ideas about the cooling system pressure control let me know.

My system is using a Mishimoto radiator because it fits perfectly in this application. Now running a 1.4 bar cap, because the stock one had weak tabs and was leaking.
The mishimoto radiator is designed for a system that uses this cap and it's 1.4 bar pressure set point, to regulate pressure to an atmospheric container or in some cases just a vent tube.

The Audi system runs pressurized as well, but but has a smaller nipple on the expansion tank that ties in with the upper rad hose (flow coming from the water manifold. Im assuming this small line should have a constant flow through it to allow the reservoir to turn over. My thought is that if this mishimoto cap is closed, there is no flow through that small line. Not allowing any flow through this hose. So I need to change my setup a little, basically modify the pressure relief valve so its open at all times, or just get (make) a cap that is a cap only and doesn't have the pressure regulating innards. If anyone has thoughts on this or a better interpretation of how the stock system works please chime in

The small hose that runs off of the upper rad hose and connects to the expansion tank is supposed to let the bubbles out of the system from where the coolant boils around the combustion chambers. Called nucleate boiling. I run Evans NPG coolant that doesn't have this problem and doesn't need any cooling system pressure to raise the boiling point.

I'd cap the small overflow hose on the rad and try to duplicate the OE upper rad hose and run the small one to the expansion tank like factory. Maybe mod the Mishimoto cap to be 100% sealed with no pressure relief and let the OE cap regulate pressure.

Just a thought

I'm doing a test.
I just went out front real quick at work and made a modification to the cap, so now that lower sealing surface that blocks off the aluminum nipple on the mishimoto rad is gone. So that hose between the radiator and reservoir is now free flowing. This is closer to original design and I think this is the way it should be anyways- I don't need two caps both trying to regulate pressure.
Does anyone happen to know the pressure setting of the relief valve in the OEM audi cap by chance?

That should help! Simpler than my idea too.

ringbearer wrote:That should help! Simpler than my idea too.

I gutted the cap to see if it changed anything. Didn't notice much difference but I think that's the way it should be.
Also going to move the oil cooler and do a fan shroud on the other side, just to maximize cooling.

Are you confident in the temp sensor? Have you tried using a thermocouple or IR thermometer to verify high temps?

The temp sender is almost brand new and pretty confident in it. Have used an IR thermometer to check temps. Pulled the rad, did some flow testing, and doing a fan shroud and some other things. May swap to the stock oil cooler or will at lest relocate to take advantage of the open duct in the pass. side of the Rs2 bumper. And mainly to get out of the way of the radiator.

I keep wanting to mention a belly pan and how they promote better cooling, but with so many people having had success without them the cause must lie somewhere else...

Have you been reusing/refililng with coolant the whole time, or straight water? (More a question of cost, and also that water has a higher specific heat capacity than glycol.)

PRY4SNO wrote:I keep wanting to mention a belly pan and how they promote better cooling, but with so many people having had success without them the cause must lie somewhere else...

Have you been reusing/refililng with coolant the whole time, or straight water? (More a question of cost, and also that water has a higher specific heat capacity than glycol.)

I have the belly pan and was going to fit it up but have been working on some other things to maximize cooling.
Have been running Audi coolant concentrate mixed with distilled h20 and refilled with a fresh batch after doing the thermostat.

New fan shroud. The shroud pictured below is going to be tacked to the radiator. I built it to shift the fan back a bit and get better use of the radiator, and also to seal as tightly as possible around the radiator.
Considering the side mounted location of the rad, I am also going to move the oil cooler to the other side of the car tomorrow, since there is an open duct there that isn't being used it makes more sense to get the oil cooler away from the radiator. All its doing is preheating the air that does go through the rad, and obstruct flow. I can get the same benefit from an oil cooler on the other side.

Nice shroud, that should make sure the fan pulls air through the rad. Do you have the most powerful fan in your size?

ringbearer wrote:Nice shroud, that should make sure the fan pulls air through the rad. Do you have the most powerful fan in your size?

I don't know if it's the most powerful but 2,300 CFM is quite a bit. It moves alot of air!
I think getting the oil cooler out of the way will offer a better benefit though.

Absolutely. It can only help, the oil cooler should be really well shrouded if possible.

Made a bracket for the radiator, rubber mounted on the bottom to absorb vibration. Finished the shroud.


Made a bracket for the oil cooler and relocated to passenger side. Went with the stock oil cooler just to see if it made any difference at all in cooling.


Oil cooler. As jim mentioned. Need a shroud for this now. Or decide if I want to swap to the bigger one and have it behind the grill.



Now I need to do a few heat cycles. Get the coolant to burp and get the air out and see how it behaves. Warmed up until thermostat opened and let it sit and idle for a long time with the fan on. Now letting it cool.

Making good progress, nice work. Hope this helps resolve the cooling issues.

Frustrated or not, your coupe is a keeper!

I am frustrated for sure but I feel like as far as the cooling goes there is something very small in front of me that I am missing.
-replaced leaky radiator cap
-I checked orientation and swapped to a new thermostat.
-installed shrouding on top of engine bay
-opened up air bleed line to degassing tank
-installed shrouding around fan
-filled with new 50/50 mix coolant
-moved oil cooler out of the path or radiator

So I'm convinced now this isn't airflow related.
If I had a problem with my brand new GRAF water pump I think I would know it. Coolant wouldn't be circulating at all. But I may have to pull that and have a look at it just for piece of mind. Still I think in the case of a bad water pump, wouldn't I just be totally overheating not just running hot?

Where is this hose going? The ~3/4" hose in top. Unless you have an aux radiator, that shouldn't be there.

It looks like it's going to your bottom port on the coolant tank. If so the system isn't going to be able to purge air from the system like it normally does. The stock design is to constantly burp the system through the coolant tank via the little hose at the top, but the return needs to be in the bottom of the radiator.

FWIW, I drill a really small hole in the flat portions of my thermostats to help bleed the coolant easier. Never had an issue getting my 4000 to bleed air out of the system properly (20vt, but same layout). On the newer cars, there's actually a hole w/ ball in it to do the same thing (By "newer" I mean my '96 A4, and the 2.7T allroads as well).

jretal wrote:FWIW, I drill a really small hole in the flat portions of my thermostats to help bleed the coolant easier. Never had an issue getting my 4000 to bleed air out of the system properly (20vt, but same layout). On the newer cars, there's actually a hole w/ ball in it to do the same thing (By "newer" I mean my '96 A4, and the 2.7T allroads as well).

I've never had an issue with these cars getting air out which is why im starting to look elsewhere, I dont think its water or airflow related. If it was it would cool down at 35+ mph.
I do wish I had drilled that hole though!

audifreakjim wrote:It looks like it's going to your bottom port on the coolant tank. If so the system isn't going to be able to purge air from the system like it normally does. The stock design is to constantly burp the system through the coolant tank via the little hose at the top, but the return needs to be in the bottom of the radiator.

Jim, the 3.4" line goes to the bottom of the expansion tank. There is no aux rad in the system. In the picture you can see a 1/4" line going to the pressure release cap on the radiator, that cap has been disabled so it has no lower sealing surface or spring, so therefore full flow through that 1/4" line to the top of the rad to burp air if needed.

I know it seems crazy, but have you considered switching back to a regular OEM type radiator and fan with aux?

I had a very similar setup to this with the mishimoto radiator on my 90 with a big turbo and I was not satisfied with it. I ended up getting hank to make me a forward facing intake, and installed a ducted radiator in the OEM spot with an aux radiator, RS2 fan shroud and 200 20v fan. Was very happy with it after that.

dana wrote:I know it seems crazy, but have you considered switching back to a regular OEM type radiator and fan with aux?

I had a very similar setup to this with the mishimoto radiator on my 90 with a big turbo and I was not satisfied with it. I ended up getting hank to make me a forward facing intake, and installed a ducted radiator in the OEM spot with an aux radiator, RS2 fan shroud and 200 20v fan. Was very happy with it after that.

I will have to look at your thread and see pics of what you were running.

I am feeling like the problem is not related to the radiator. What kind of temps were you seeing?

The issue with re-engineering the whole setup is:
1) cost: I dont have a stock radiator and new radiators are very expensive.
2) limited location: with the AAN intake manifold a stock coupe radiator is too wide, and I also dont have one. I have a very limited space to put the rad so I need to maximize flow as able.
I also want to make sure there is not something going on somewhere else before I go through the process of redesigning the whole thing. I can't fit one in front of the car unless maybe if I was to get a new intercooler and relocate that.
3) Most importantly, I never had a single issue controlling temps last summer, so what has changed?

dana wrote:I know it seems crazy, but have you considered switching back to a regular OEM type radiator and fan with aux?

I had a very similar setup to this with the mishimoto radiator on my 90 with a big turbo and I was not satisfied with it. I ended up getting hank to make me a forward facing intake, and installed a ducted radiator in the OEM spot with an aux radiator, RS2 fan shroud and 200 20v fan. Was very happy with it after that.

So you went from this:


To this?



What temps did you see before and how did it look after?

I could possibly do something like that but ill need to make a new intake manifold from scratch.
I do have this which i cut and sandblasted, to use for a new custom intake manifold. But the fitment up there is very tight with where the PS pump sits on top with the AAN setup.

yep, that exactly what I did. Not pictured in the second pic, was a bung welded to the radiator so I could run the factory aux rad.

Honestly, I don't remember what temps I saw before and after. The first setup ran ok crusing around, but would get warm going slow and take a long time to cool down. I never really ran the car hard with it that way because i didn't like how the temps climbed so quickly.

I didn't have a power steering pump up there, so that made my manifold situation a lot easier.

Side mounted radiators kind of suck either way really. I'm excited to have a b3 with a front mounted rad, but obviously that doesn't work so well on a 5 cylinder setup.