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2G Overheating Issue

TSIdad

Probationary Member
29
22
Apr 1, 2021
Nashville, Tennessee
Freshly rebuilt motor on my son’s 95 TSi. .2 overbore, Wiseco pistons, Eagle rods, ACL race bearings, ARP main and head studs, new water pump, new radiator (OEM) new radiator fans (Mishimoto), new hoses, new thermostat, fresh coolant fill, burped, and topped off.

Tested for a blown head gasket and it’s clear.

We did add an FMIC with this build, but the location doesn’t seem to be different from others I’ve seen. The car didn’t come with a lower heat shield for the turbo, so it melted the drivers side fan. We’ve since replaced the fan and added a new heat shield.

Driving around 30 mph runs just a bit over operating temp, but as soon as you give it the beans or get up to speed on the interstate it spikes and overheats.

I’m out of things to test 😞

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TSIdad

Probationary Member
29
22
Apr 1, 2021
Nashville, Tennessee
Rebuilt the injectors and took her for a long test drive but she started overheating so we went home. I’m actually out of solutions at this point. Everything is brand new, radiator, 3 fans, water pump, thermostat, even the ducting. Any last suggestions before I stick a for sale sign in the window LOL.

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TSIdad

Probationary Member
29
22
Apr 1, 2021
Nashville, Tennessee
It’s been overheated enough at this point maybe need to look at a possible head gasket?
We ran a head gasket check, several times actually and it checked out fine. The more I think through it I believe we may have a tuning issue. It primarily overheats during boost and WOT. It stays cool while driving around town, but onramps and the interstate it heats up. Maybe it’s getting lean on boost?

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pauleyman

DSM Wiseman
8,187
2,757
Nov 19, 2011
oklahoma city, Oklahoma
I'm gonna say test the fans and make sure they're spinning the right way. Further still get rid of them and install oem. Lastly check temp at ecu instead of the gauge. You will double check it isn't just the gauge.
You might also do a leakdown test if you haven't.
 

We're on Boost

15+ Year Contributor
1,542
385
Aug 25, 2007
Seattle area, Washington
I would try taking the thermostat out and test driving it that way. It might make a difference. On my 1g it does. Even if you don't want to run it long term without a thermostat, it still might tell us something to see what difference it makes.
I notice in pictures that the 2g thermostat is different, it has another like valve plate on the bottom that moves when it opens. I don't know what that does and what effect to watch out for if you don't have that. The 2g guys should know that. The 1g thermostat isn't like that so I have no experience with it. If that lower valve blocks off a bypass, then the engine would probably actually run hotter without it.

There is also a different 2g thermostat that you could try. It's over priced, but I've seen 1 or 2 people post that it helped them. It's the Mishimoto MMTS-ECL-95TL which is a 155 deg F thermostat. All the regular DSM shops like STM, MAP, JNZ, Extreme PSI, and Amazon sell them. Here is the actual Mishimoto page:


I don't know why Mishi lists it for 1997-98 Talon Tsi rather than 1995-1998. The other shops mostly just say 1995-1999 2g DSM. Rock Auto shows all the same thermostats for 1995 Tsi that they do for 1998 Tsi so I think Mishi just messed up when they wrote their "Fits".

If you do decide to run it without a thermostat in the summer, it would be a good idea to use anti-freeze of the type that has organic corrosion inhibitors rather than inorganic (silicate) inhibitors. Just about all of them now are the organic type (OAT, POAT, HOAT, etc). In other words not an IAT type. This is because organic types protect aluminum from cavitation damage a lot better than the IAT type, supposedly. The antifreeze you already have is probably good. Usually the IAT types are green.

I agree that the gauge could be off and it's better to read it from the ECT sensor that goes to the ECU and you log it with ECM link. That sensor can be off too. I've got 3 of them and they all test a little different.

If it is getting lean on boost, you would definitely want to know about it. It would probably be causing knock. Logging a wideband would be the way to get a good look at that. And looking at your "Knock retard" in DSM link, or whatever the equivalent item is for 2g.
 
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DSSA

Supporting Vendor
637
442
Jul 26, 2002
Hatfield, Pennsylvania
The head gasket is blown between the cylinder and a water jacket. You've got the classic, text-book symptoms.

No amount of "improving the cooling system" is going to fix this.

Want proof? Take off the coolant cap, idle up to full temp and whack the throttle---just stand back as the coolant system will pressurize and fountain out of the open port soaking everything around it in hot coolant.

Have the cylinder head deck checked as well while you have it off, as you probably have warping of the deck at this point as well. Clean the block surface and check that carefully with a straight edge and a feeler gauge as well.
 

TSIdad

Probationary Member
29
22
Apr 1, 2021
Nashville, Tennessee
The head gasket is blown between the cylinder and a water jacket. You've got the classic, text-book symptoms.

No amount of "improving the cooling system" is going to fix this.

Want proof? Take off the coolant cap, idle up to full temp and whack the throttle---just stand back as the coolant system will pressurize and fountain out of the open port soaking everything around it in hot coolant.

Have the cylinder head deck checked as well while you have it off, as you probably have warping of the deck at this point as well. Clean the block surface and check that carefully with a straight edge and a feeler gauge as well.
The head was just decked, new head gasket installed, cylinders honed, all new forged internals, and ARP main and head studs. We conducted a head gasket test and it came back clean.

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Dericsh

Supporting Member
1,334
563
Nov 25, 2002
Pearl River, Louisiana
The head was just decked, new head gasket installed, cylinders honed, all new forged internals, and ARP main and head studs. We conducted a head gasket test and it came back clean.
Composite or mls gasket? Just curious.

It’s been overheated multiple times since the pictured test, right? Do you have access to an air compressor and leak down tester?
 

DSSA

Supporting Vendor
637
442
Jul 26, 2002
Hatfield, Pennsylvania
Did you test it like I suggested?

From your earlier comment "It overheats mostly under boost".

If you're watching the temp gauge instantly swing up while under boost (and it's accurate)---it's leaking SOMEWHERE from the combustion into the coolant system. Otherwise, you're not going to heat the coolant that quickly.

Doing what I said above will tell you if that's happening---in moments.

A pressure test may not show this---a pressure test is not going to mimic a car under full boost, nor is whacking the throttle at operating temperature, but it comes a lot closer. The gasket could be sealing enough until the temp and pressure rise enough to cause lift.

Your call--but that's what I've seen time and time again with issues like the above.
 

We're on Boost

15+ Year Contributor
1,542
385
Aug 25, 2007
Seattle area, Washington
You mentioned that you had to reverse the way the Mishi fan plug was wired because it was backwards. Was the fan actually made to be a pusher fan rather than a puller? If it was made to be a pusher, the fan blade contours could be all wrong for using as a puller. A proper blade is concave on one side and convex on the other. A puller has to have the concave side facing away from the radiator. "Reversible" fans most likely have "flat" blades (they might have twist but the airfoil cross-section shape is a straight line). I would avoid those because that type of blade is not highly efficient in either direction.

Is the car still not tuned? Thinking about air/fuel ratio, and knock.

It looks like you still have an OEM type radiator which I think is a single row radiator. A 2 or 3 row aluminum radiator might help quite a bit.

I think your fans are all run by a switch on the dash and are not controlled by the ecu. That would be good. Because if any of your fans are contolled by the ecu, you've got that fan table that's in the 2g ECU controlling fan speed, and you don't want that. I forgot in an earlier post that the 2g has that. There's a table in the 2g FSM that gives the temp vs fan speed specs and it's ugly. You should have the fans running most of the time unless it's just not needed, like in cold weather.

Have you tried driving it with the nose taken off the front of the car? If that made a big difference it would be interesting. The way the air opening (grill) is sized and located in the front of these cars is kind of wrong for having an FMIC. The upper part of the radiator doesn't get direct airflow because the grill opening is too low. That's a shame because the upper part of the radiator isn't blocked by the intercooler. The upper part of the radiator should get a lot better airflow if the nose is off, and I would try that out a little just to see if it makes much difference.

But if it is a blown head gasket you'd want to know that right away.
 
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randman2011

Proven Member
517
239
Feb 26, 2012
Indianapolis, Indiana
While I can't really help with the overheating beyond what others have posted, I can say that with a large FMIC attempting to cool a maxed-out turbo, full AC, the stock radiator and fans, and zero ducting whatsoever, I never had temperature problems even in extreme weather during autocross. Something is definitely wrong here, and an intermittent head gasket leak fits well.

I had a GST Spyder as my first and only car for 6 years and while it needed stuff, it was reliable and never stranded me anywhere. And when it did break it was never anything that my 16 year old self couldn't fix. That was over a decade ago and while I still hold that they can be reliable enough to be a DD without much effort, it would be best to have access to a second car just in case. Which it sounds like he will.

Also, you need MB914136 to fix that front bumper crease on the bottom. Actually, I need one as well.
 

GSXRunner

Proven Member
106
23
Feb 24, 2013
Queens, New_York
I know you put a new radiator in, but it's possible that it could be restricted; maybe a manufacturing defect. I would take it for a drive, get it nice and hot; then probe different spots on your radiator with your infrared temperature gun. Look for cool spots where coolant isn't able to flow through. There shouldn't be any sudden temperature differences as you scan the surface. I know it's very rare for this to happen, but this easy check could save you a lot of time if it just happens to be the case.
 
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