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Old 10-23-2020, 06:19 PM   #1
daniels740
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Default 740 Interior Leak and Coolant Reservoir.

Never have I wanted to get rid of the 740 more than I have these past few days. Let me give you guys a rundown of the problems.

First, my drivers side carpet in both the front and rear are SOAKING wet. I removed the carpets and foam and they are drying now. The passenger side is bone dry.

I can't seem to find any place suspect for leaks. From inside, it was obvious that the water didn't come from the dash or around center console, making me think it may be the seal in the fender. I haven't been able to reproduce the leak, though. I even poured water into the sunroof drains and they all drained beautifully. Then, I looked in the engine bay around the wiring loom seals, etc. They are fine. But then, I discovered a different problem.

I noticed that my coolant expansion tank was empty. Last time I looked, maybe a week ago, it was to the max line. At first I wad thinking my heater core blew and somehow I didn't realize it was coolant inside. I decided to put some more coolant in the tank only to realize the reservoir split at the connection to the hose underneath. The engine never overheated, and the rest of the system seems full.

Anyone know if the aftermarket reservoirs are any good? OEM Volvo is $85 while the others are a fraction of that.

Also, where should I look for leaks? What are the odds that its the large seal on the driver's side fender?

Thanks in advance. I hope to get the '89 740T back on the road soon.
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Old 10-23-2020, 06:41 PM   #2
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I decided to give it another good spray with the garden hose and this time I found some water... in the back, and it seems to have come from under the driver's seat. It could be water that has pooled up since I removed the carpets, though.

Last edited by daniels740; 10-23-2020 at 07:17 PM..
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Old 10-23-2020, 07:40 PM   #3
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Anyone know if the MTC brand aftermarket coolant expansion tank is good? I want to get an order in as soon as possible, and just want to know if they're known to fail or anything.
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Old 10-23-2020, 07:54 PM   #4
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Reseal the plastic panel by the drivers left foot. It's an air hole for non AC Euro cars.

Goop it up good.
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Old 10-23-2020, 08:11 PM   #5
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Reseal the plastic panel by the drivers left foot. It's an air hole for non AC Euro cars.

Goop it up good.
Do you know how to check if that panel leaks? Like where would I have to spray water outside for it to leak around there, in order to confirm that it is in fact my problem.
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Old 10-23-2020, 08:25 PM   #6
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The cowl.

You should also pull the cowl, clean all the leaves out, reinstall the mesh screen, and reinstall the black plastic cover for the blower motor. Use butyl tape. Water can get down into the HVAC case here too.
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Old 10-24-2020, 01:35 AM   #7
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https://turbobricks.com/forums/showthread.php?t=341184

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Old 10-24-2020, 10:14 AM   #8
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I sprayed water at full pressure into the cowl from all directions, and no leak. I also sprayed the windshield, cracks between the doors, and the sunroof. I have yet to find a new droplet of water inside the car.

Is there any place where water could infiltrate from underneath when driving? What am I missing?
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Old 10-24-2020, 10:20 AM   #9
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Clogged sunroof drains?
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Old 10-24-2020, 10:25 AM   #10
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I can't recall the brand, mtc may have been it, but I've had aftermarket tank for 5+ years and no problems. The one I got had the fluid level float in it so I added the low level warning light to the dash, which would alert you to a leak in the future. This is the newer rectangular tank, not sure if your 89 uses that or the round one.
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Old 10-24-2020, 10:43 AM   #11
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I have the round tank.

Also, I found the leak! It is around the brake booster. Should I seal it up with butyl tape or plumbers putty? I have both. If there is anything else that works well I'd like to know.

Also, my engine bay seal that connects to the cowl is no longer good. Any thing aftermarket I should give a try or should I post in the wanted section?
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Old 10-24-2020, 11:13 AM   #12
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Quote:
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Anyone know if the MTC brand aftermarket coolant expansion tank is good? I want to get an order in as soon as possible, and just want to know if they're known to fail or anything.
Only buy genuine Volvo for coolant tank.
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Old 10-24-2020, 12:09 PM   #13
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are you running straight water for coolant, Florida Man?
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Old 10-24-2020, 12:20 PM   #14
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are you running straight water for coolant, Florida Man?
No, LOL, I run premixed 50/50, and I've never head a leak heretofore.
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Old 10-24-2020, 12:28 PM   #15
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No, LOL, I run premixed 50/50, and I've never head a leak heretofore.
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Old 10-24-2020, 12:31 PM   #16
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I wonder whether using Plastic Weld (or similar product) would result in a lasting repair for the crack on the coolant reservoir?
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Old 10-24-2020, 12:36 PM   #17
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I wonder whether using Plastic Weld (or similar product) would result in a lasting repair for the crack on the coolant reservoir?
I'll try to get a pic up tonight when I can work on the car and fix my interior leak. It's practically impossible to try one of those products in the location where it failed.
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Old 10-24-2020, 01:36 PM   #18
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Like mentioned only use OEM for the tank, itís too important
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Old 10-24-2020, 04:23 PM   #19
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Lots to choose from on ebay.
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Old 10-24-2020, 05:52 PM   #20
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Lots to choose from on ebay.
I'm pretty sure replacement is the only viable option!
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Old 10-24-2020, 07:03 PM   #21
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Iíd bet thatís the original tank. Look how many years it lasted, aftermarket just donít last
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Old 10-24-2020, 07:29 PM   #22
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I just sealed up around my brake booster, and the leak seems to be cured. I will put up a wanted ad for the engine bay seal. Thanks for all the help.
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Old 10-28-2020, 05:10 PM   #23
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As it turns out, the fender seal also has a tiny leak that needs to be addressed. What product should I use? Is sealant that comes in a tube like caulking good? You know, the stuff that you should never mistake for regular caulking cause it sticks like a to your hands.
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Old 10-28-2020, 06:16 PM   #24
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I just RTV it up.
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Old 10-29-2020, 06:38 PM   #25
daniels740
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Quote:
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Reseal the plastic panel by the drivers left foot. It's an air hole for non AC Euro cars.

Goop it up good.
I hope this fits that description.


Not the prettiest work, but I'd sure be surprised to see a single drip of water come through.

Thanks for all the help.
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