Question for the intelligentsia:

My rear window seal failed on my Subie-swapped car, and I've noticed the firewall gets really warm. There's no backpad (yet), but there is a layer of sound deadening on the inside. No engine compartment pad, either. I can feel the heat radiating off the firewall. I haven't taken the temp, but I'd guess it's 120-130 degrees. Perfect for those 90+ degree summer days. The fresh air fan is not installed (yet) either, and my ice-powered swamp cooler contraption just can't compete.

Driving home yesterday, I noticed the window glass was actually warm to the touch and thought perhaps the heat is causing the butyl seal to soften and the weight of the glass pulls itself off.

I recently put the stock air flaps underneath in the hope that they would draw more cooling air through. No discernable difference.

Anyone else getting that kind of heat from their engine compartment? Would the engine compartment pad help? How do others get the heat to flow out?

Thanks,
Tom

May want to to switch to Urethane. Obviously it's getting very soft. In the VW version the heat stays on the bottom of the engine and has seals to keep the heat from rising up into the the top. Even though your car is water cooled, I'd bet you have way more heat in the engine compartment.

I took these temps about a month ago on my recent 2.5 Subaru build just to see what was going on with my car. Note: radiator is in the front of the car. One of those smaller VW Sirocco radiator units. Engine sits back away from the firewall about 10" or more so there is a big space there, and I have not installed my engine lid yet so it is wide open to let the hot air to rise out. Coolant temps at the gauge is about 190ish. Temps as noted measured with a cheap HF infrared thermometer. The key could be in the engine lid removed or going with a GT style with full open venting. Hope this helps.

Air temp100d sundown

Engine intake iron manifold runner mid point 152d

Engine top of alum cylinder head L 170

Engine top of alum cylinder head R 175

Alum intake tube steel support bracket 135d

Alum intake tube at 75d bend 122d

Alum intake tube at mid point 121d

Alum intake tube at air cleaner 116d

Fuel tank top center 106d

Firewall front trunk radiator side at Moroso125d

Alum expansion tank center 126d

Firewall front cabin side metal 104d

Console tunnel top - 3" behind shifter 101d

Cabin floorplan cabin side on butyl insulation.

Cabin perlon carpet passenger side feet area 100d

Firewall back engine bay side midway 114d

Firewall back cabin side carpet 103d

Rear trunk decking mid point

Radiator hose front 145d

You didn't mention that you were using a GT engine lid, so I guess the assumption is that you're not. But I would think that a GT lid would let heat rise to the window before a normal lid would. Which do you have?

I do not have the GT engine lid… just the regular one - without a rain tray. I can see how the stock engine lid might hold hot air up against the cabin firewall. Motor seems to be getting plenty of air to breathe, but I agree, lots of hot metal in a small space. The turbo is up high near the firewall to the trunk. I’ll try running it without the lid and see if it makes a difference.

Radiators for motor and intercooler are up front- fender well cut outs to vent hot air out. Coolant lines run through the longs (same as stock, just water instead of hot air). Supply on one side, return on the other. They’re likely adding heat to the cabin, too.

Thanks for the tips!

My rear window seal has failed at the bottom. When I clean the window it moves away from the seal. I also think this lets in some engine noise. I hope to pull the glass out in the next 2 weeks and re-seal it. The timing is good because I sourced a different heated rear window that is supposed to be in excellent shape. ValcoOscar was kind enough to bring it up from LA and it is now at the Red Barn. Thank you @ValcoOscar . I am going to take a ride next week to pick it up. I hope it is a good window. Mine has some minor scratches so I wanted to replace it. Will do the glass and seal at the same time.

Thank you Tom, one more reason not to lump a 914!!!

Not certain how water cooled vs air cooled impact heat inside the engine bay, but would have to assume the heat from the exhaust would still saturate the engine bay if not blocked and sealed.

I would suggest that the lack of upper/lower separating sheet metal tin is exacerbating your situation.

In a properly-tinned and -sealed Type 4 engine, there should be minimal under-engine air - the hot stuff - rising and mixing with the top side of the engine. That's the reason for all that tin and seals, so that the engine cooling intake fan (and induction) is pulling in cool(er) air from the grill area.

Unlike the Type 4, in your case you have the engine, cooling, exhaust (the hot stuff) all exposed to the upper side of the engine compartment...and heat rises.

Somewhere in here I've "documented" my own air temp tests on my Type 4. Not as solid and numerous as listed above, and I did mine using a 4-probe BBQ temp set, but I saw air temps in line with 110-120 max on the top side of the engine in really high ambients and really hot underneath.

Maybe try installing some kind of upper/lower separating sheet metal?

Edit: Depending on how airflow is mixing with that installation, it may help to install some small 12V fans in the grill area to promote grill-downward airflow.

I'm going to suggest that the temperature is probably not your problem.

Butyl will easily withstand interior temperatures generated by sun load. Not uncommon to see interior temperatures as high as 160 F in Phoenix with full sun load, windows up.

Butyl has been used for years with these sorts of desert southwest, hot ambient / hot interior temps without having glass de-laminate from the butyl.

Maybe it wasn't installed onto perfectly clean glass and/or has become contaminated somehow? Likewise, the rear glass should be supported on the bottom by a couple small rubber pads. The Butyl should not be expected to bear the weight of the rear glass alone.

spacers are item #15:
http://www.autoatlanta.com/porsche-parts/h...;section=805-00



Specification for Butyl tape found quickly on-line:
Specification:

Solids: 100%
Service Temperature: -60°F to 275°F.
Application Temperature: 35°F to 110°F.
Bonding Time: Immediate water tight seal. Full bond in 24 hours.
Shelf Life: 24 Months
Tensile Strength: 25 pounds per linear inch.
Water Resistance: Excellent
UV Resistant: Yes
Cold Temeperature Flexibility: Excellent, passes 1/2" mandrel bend @ -60F.

I seriously doubt that your back window is going well beyond the max service temperature unless the exhaust and turbo are right there. If in doubt - measure the glass temperature and/or air temp right in the vicinity of the closed engine lid right below the glass.

When I took my rear window out, the butyl tape was totally unattached. I'm thinking just age was the culprit, it was still an air-cooled motor.

The other option is to put black duct tape at the bottom. Also makes a nice cosmetic edge.
We also include the spacers in our kits as we know the butyl will get hot and you never want tempered glass touching metal. It will pop.
https://914rubber.com/front-or-rear-reseal-kit-for-914-1

Also we make the tinted rear windows. I run one on my 914 and it takes a lot of headlight glade out.

Window-
https://914rubber.com/glass-rear-window-1
No pic on the website I will put up a pic here shortly. They are tempered glass.
-Mark

That’s exactly what happened. I noticed it after washing and there was water inside the car. But by then the butyl was wet and wouldn’t reseal. My short term fix was a strip of Gorilla tape, which has held up pretty well.

I think Superhawk figured it out. I don’t remember having those little rubber blocks in there, AND the butyl tape was definitely not “fresh” when I installed. I didn’t realize the stuff has a shelf life.

@Mikey914 the website says you’re out of stock on the butyl kits. Any idea when it will available again?

Thanks to all- well almost all- for helpful ideas and judgment-free insights.

Let me double check, and I'll let you know, should have some in stock.
Mark