Transmission overheats despite external cooler

[Endopotential]

First off, Happy Thanksgiving to everyone! I've learned so much about car mechanics and overall DIY'ing from all you kind folks.

Now on to business. Abscate will surely see this as proof positive why external coolers should be banned from the Eurovan world.

I've got an '02 Weekender with 130k miles and an external cooler that some previous owner installed. It drives fine on the highway, logging transmission temps of about 180F at 65mph. But in stop and go traffic, or crawling up a windy mountain road I've seen temps get over 230F. At which point it usually has trouble finding gears and goes down to a crawl.
The temps are determined by a gauge I've hard wired into the transmission, along with readings I've finally been able to get on Torque Pro. I changed the fluid not long ago, using both my analog gauge and and IR thermometer to determine what I think is correct temp for the overflow.

I'm taking the front off as part of a project to update the radiator coolant side of things and noticed that my trans cooler is about half the length of an LDP49211. And the routing of the hoses behind the steering fluid cooler probably doesn't help either. Would this be enough to cause the transmission to overheat under duress?

I'll plan to upgrade to a bigger cooler regardless. I had been lulled into false security because the coolant temp gauge is always pegged at 190F in the middle. Torque Pro readings have shown as high as 210.

I also noticed recently that my radiator fans weren't running when things got hot. I've since replaced the two green resister coils, and can get the fans to run at both speeds by jumping the 3 prong cable. But haven't gotten it back on the highway to test things out again.

Is there anything else I should look at?
- Do these transmission coolers or hoses ever clog up? What pumps the fluid around in the first place, is there a small pump within the transmission?
- Does it matter which hose plugs where into the cooler?
- I read about some other radiator temp sensor/controller down by the transmission. Is this different than what is plugged into the thermostat housing?

I'll be doing the whole thermostat / coolant crack pipe as part of this. Wow, it's deeper into the engine than I've ever worked. Any advice or tips?

[mikemtnbike]

Does the cooler installation have a thermostatic valve (to stay closed while cold) that might not be opening?
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1991 Vanagon GL 2.1 AT Westfauxlia. "Frankie" Totaled https://www.thesamba.com/vw/forum/viewtopic.php?t=764510&highlight=carnage
1995 Eurovan Camper "Marzivan"
2020 GTI SE manual

[Stripped66]

[Endopotential]

Thanks for the replies so far!

Just to double check my understanding of the concept, as maybe it's so basic most discussions skip over this entirely - the standard external cooler bypass mod removes the OEM kidney shaped metal box, and the hoses just plug directly into the transmission itself?

That looks like what I have. My hoses plug into the transmission, and no thermostat switches along the length of those hoses. I do see where a radiator coolant hose got spliced together down by those Sonex connectors, so I'm assuming the radiator did get bypassed on my van.

[mikemtnbike]

agree about the fans, missed that- would check that first.
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1991 Vanagon GL 2.1 AT Westfauxlia. "Frankie" Totaled https://www.thesamba.com/vw/forum/viewtopic.php?t=764510&highlight=carnage
1995 Eurovan Camper "Marzivan"
2020 GTI SE manual

[Endopotential]

About the fans, how should I go about testing them?

Unplugging the 3 pin connector on the right side, I can jump the terminals and get both fans to go in both low and high speed (not sure how to get it into the secret turbo 3rd engine's-gonna-blow-up mode).

If I have the engine running and turn on AC, it will also run in high mode.

So is it just a matter of getting the engine up to like 180F (somewhere around there?) and making sure low speed also turns on?
Is there a situation where only one fan is supposed to run, and not both?

[Stripped66]

[rizzag]

the Tru-Cool LPD49211 is a fantastic cooler, that fits perfectly behind the grill. It is the one I run. I believe they are still on backorder from Tru-Cool, but amazon options are available (this is the exact one I ordered).

https://www.amazon.com/CHERISH-AUTO-1PCS-OEM-LPD49...amp;sr=8-2

I had a smaller cooler that was on it when purchased, adding the 49211 dropped the temps 40 degrees over the other aftermarket cooler.

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flossin, tossin, dippin, and trippin

[OB Bus]

[VanGeek]

Piling on based on my experience.
I have read there are two different OEM coolers. A 4 pass and 6 pass that was introduced later perhaps in 2002. The 6 pass is more efficient.
My OEM cooler ran hot. Even under flat highway speeds the cooler would routinely hit 230.
I added an external cooler with integrated bypass earlier this year. https://www.thesamba.com/vw/forum/viewtopic.php?p=10274807#10274807 After about 5k miles of driving experience, I've observed that the trans runs much cooler. Typically around 160 to 170 at highway speeds in the aummer when warmed up.
The OEM cooler facilitates trans fluid warm up by regulating trans fluid temps via engine coolant. So with an external cooler and no oem cooler, the trans fluid warms up much slower. Even with a bypass there is no active warming. Especially when outside temps are cold. This is less ideal vs quick warming of the trans fluid. If the van is frequently driven in severe cold winter conditions you may want to consider this downside.
Under thermally challenging stop and go conditions and low speed ascents in the summer, my OEM cooler got very hot. Sometimes 260+. The external cooler also performs hotter under these conditions, however, it has never exceeded 230 and most often is in low 200's under these conditions. So for me, the external cooler outperforms the OEM cooler under all hot and challenging conditions.

The cooler your PO installed is a lot smaller vs other recommended solutions and is likely under sized. The gowesty solutions seems well engineered and worth consideration. I'm also satisfied with my DIY solution

[Endopotential]

Got my upsized cooler installed, it's more than twice the size of the old one. So far so good, just glad it's not squirting out transmission fluid on startup.

Took it for a test spin up and down the hills of SF, and transmission temps haven't gotten over 180F yet. Looking forward to putting it through a full test soon.

[EuroTec]

Bigger is better when it comes to oil coolers.

The 01P is a POS transmission. In my years of working on cars I'd say it's the number one failing transmission VW ever made.

That said, doing a manual swap is so worth the cost and effort. It makes the Eurovan a solid reliable beast that hauls ass!
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If it ain't broke, don't fix it!

[Endopotential]

@Eurotec Man, if you weren't on the other side of the country I'd be very tempted indeed to have you do the conversion.

I love tinkering in the driveway, but that would be a project that would totally exceed my capabilities. Also too bad that usable EV EV conversions are nowhere on the horizon.

Hope you're all recovering OK from the storm.

[Endopotential]

Just to close the loop on this story -

I took the van back up to Mendocino / Fort Bragg with the 300lb dirt bike in back. Wow, what a difference this little tweak makes!!! The Westy drives like a normal car again

The last time, going through the coastal mountain range the trans went up to 230F and started slipping gears. This time it stayed around 145 almost the whole trip. Peak was 180F in stop and go traffic coming back through SF.
Now I'm wondering if things are too cool? I can't find any good data on what is too low - some web postings say anything below 150F is "ideal". It seldom gets below 50F here on the California coast, so I'm not as worried about fluids staying too cold after startup.

The LPD49211 cooler is about 2.5 size of the old one. I'm just surprised how much of a difference it makes. Not only does it keep baseline temps low, but when things heat up, it really brings temp back down when the stop and go ends and the car sees some good airflow.
I also replaced those green coil resistors during this tuneup, so ensuring the radiator fans are working properly likely helped out as well.

[rizzag]

Your experience is exactly what I see too, temp/driving wise. I barely drive mine in the winter, but if I did, I would probably think about the Tru-Cool thermal bypass.

[CH47AV8R]

Yes, The 2001 OEM transmission intercooler was undersized and ineffective in cooling the transmission fluid to keep it below 220F under load & high ambient outside temperatures. However, the 2002 & 2003 updated coolers were no better. The best solution is an external large cooler with a thermostatic valve and removal of some hoses and NOT use the plastic hose barb GoWesty provides in their kit. It's just another failure point that can be by passed with a brass hose barb and two proper hose clamps. I added protection to the two transmission fluid hoses from the transmission to the external cooler. Note: I did remove the lower valence for the cooler installation. It was replaced once everything checked out ok with no leaks.

[Endopotential]

Thanks for the extra pics, that should help out some future DIY'er.

But as both of us live in the SF Bay Area where it almost never gets down to the freezing point - and I've yet to take the van on any extended trip to the Arctic - I don't see the need for that thermal bypass. Just another potential point of failure if that thing seizes up, along with 4 more places where things can leak.

[Endopotential]

Another trip update.

Took the van on a whitewater kayaking adventure into southern Oregon. It was about 90F crossing the pass by Mt Shasta, and the transmission temps maybe got to 180F at max. The van drove up and down the mountain like a champ.

Prior to the cooler redo, the trans would have gotten past 230F and would really have trouble finding the right gears. This repair definitely breathed new life into the 20+ year old beast!
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2002 Eurovan Weekender