Coolant leak mystery

[Eskozki]

My 944 leaves a puddle on the ground after cold nights. when hot the system holds pressure and I see nothing leak. After the night it has leaked to the point that level is on minimum. So I add a little coolant and same thing happens. Leak comes from the front and I can see coolant on the side of the radiator. When weather is warmer I do not see a leak.

My friend has a 360 volvo with similar plastic ended radiator and he has the same issue. Could this be that plastic and aluminium shrink with different rates and this causes the leak? I wonder if there is all aluminium radiators for these cars?, if you dont count the chinese ebay rads.

[walfreyydo]

You have to identify the specific location where the leak is originating from. It could be a loose/cracked hose, or it could be a crack in your radiator, or something else.

We have no way of knowing..

If the radiator is cracked youll need to source a replacement. I think there are all aluminum versions out there if you google, or perhaps others can chime in.

[Eskozki]

Both ends are wet, drivers side more than the passenger side. During the day the car can be parked and there is zero coolant loss. During nights that go near freezing temps there is a a small puddle. Now I noticed that After adding coolant it drained from the overflow. maybe the expansion tank doesnt have adequate size to allow the coolant to expand from 0°C to 100°C. Next time I'll add nothing and see what happens. I'm 90% sure its the plastic ends but if its due to material choices new rad would leak too in cold weather right?

[walfreyydo]

I think properly working radiators, plastic or not, dont leak in cold weather so I think you are overthinking that a new plastic one would potentially leak again...

A crack in your current radiator could potentially get larger in cold weather (when things cool they shrink, besides water that is) explaining the situation you describe. But you could also have a cracked hose, loose hose connection, or clamp which is causing the leak when it cools too and since the hoses connect at the sides of the radiator, this could potentially mimic a leak from the radiator itself. Point is, you need to actually find the crack or source of the leak before moving forward, unless you are ok spending the money on a guess.

Follow the puddle up and locate the highest point where you can see evidence of fluid, understanding that flow patterns usually go from the top down, but can also move horizontally along under surfaces sometimes. It might require thorough cleaning of the area first and then letting it sit until the problem comes up again. Investigate for any cracks, or if there are hoses nearby check to see if the underside of any hoses have drops of coolant perched below them.

New radiators arent cheap, so you are going to want to be 100% sure its the radiator before dropping the coin on a new one (you can also roll the dice on used). They do make coolant pressure testers which could help in your case identify where the system is losing pressure (source of the leak). The pressure will force fluid out of wherever you have leaks. The system should hold pressure. You may have no choice but to remove the old radiator and pressure test it outside the car, if you cannot adequately see or pinpoint the location of the leak with the radiator in the car due to access.

Something like this (they might be available to rent from Autozone or Oreilys as well):
https://www.harborfreight.com/radiator-pressure-tester-kit-63862.html?utm_source=google&utm_medium=cpc&utm_campaign=12144811130&campaignid=12144811130&utm_content=117789289918&adsetid=117789289918&product=63862&store=797&gclid=Cj0KCQjw0tKiBhC6ARIsAAOXutnftoewv85FZeTijjMa 2kN6k5VlOqgp3PEBkfI_D7XDW3UeC3XmVcQaAqw3EALw_wcB

There are also places that do radiator repair, but I think those are mainly for aluminum radiators which can be welded. Maybe they can epoxy the plastic ones, not sure. Usually when coolant drains from the overflow its because its overfilled or overheating (boiling and needs to relieve the pressure).

[OK-944]

Take a very close look at the rubber o-ring which surrounds the temperature switch (drivers side, high up on the side of the radiator). See if there are signs of wetness and/or corrosion around this.

The reason I say this is because I, too, experienced the "cold weather drip" recently, which has gone away as the weather has warmed. From what I can tell, the leak originates from that o-ring, possibly as a result of some kind of shrinkage with the cold.

Thing is...I'd replaced that switch fairly recently. I'd had a further thought that I'd used the incorrect coolant, which was starting to eat away at that o-ring...but as the stuff I use is both phosphate and silicate free, I should be fine. So perhaps I did not torque this switch down tightly enough? I plan to get after this soon, and will see if I can turn it in a bit more...knowing that I'll likely not know how effective this will be until next winter!

I'm guessing that a similar cold-related leak could occur from the little blue plastic cap, which serves to empty the radiator. Thing about those caps is they're flimsy and I never use this to empty my radiator, but instead simply pull off the lower radiator hose on the passenger side. Good luck!

[djnolan]

there is a nipple that is threaded in to the radiator on the drivers side that can leak too. however if it is leaking on the cooldown, maybe the overflow tube has a leak as the coolant goes back into the radiator from the coolant tank.

[Eskozki]

Near the thermoswitch is wet, but i have a new thermoswitch waiting for install (PO messed the wiring need to rewire to get the proper 3-prong switch working) There is no O-ring in the packing? Only a metal crush washer?

[Monkey Wrench]

you might remove the rad, plug the holes for the rad hoses by stretching a hunk of inner tube over and a hose clamp. try to pressurize it to about 15 PSI through the hose connection to the bottle. not too high. put the rad in a vessel of water so then you can see if it's bubbling and where.

Pressure affects the boiling temp so the system is designed to withstand some amount of pressure. that is usually set by the spring on the cap of the reservoir bottle. If the system were open and had no pressure then it would boil over more easily.

Id look around the waterpump first, make sure that isn't leaking. also if you have a blown head gasket it can force air into the water that was meant to go out the exhaust or water out the tailpipe so keep an eye on the tailpipe for any signs of abnormal steam. If you sense antifreeze out the tailpipe that might mean you have a head gasket issue, hope not. if you do have a head gasket issue the first think you may notice is the level in the water bottle is going all weird and varying.

whatever rad you use it needs to at least be able to withstand the makeup fluid bottle cap pressure. it might be written on the bottle cap, maybe around 15 to 17 PSI or similar. It's probably documented.

don't go putting high pressure in the rad or it will surely cause a failure. Its not meant to take a lot of pressure, but some. You might be able to pressurize the system in place via the water bottle cap or a Tee in the line. what you can likely do if you have a compressor is turn the tank pressure down to 15 PSI or so then connect it , then it wont go over the limit because that's all the pressure your compressor has in it's tank , to supply. then you may be able to leave it pressurized and look around before needing to remove the rad. If you have a leak it may become evident. In normal use the system won't see pressure until the engine is up to temp. If you want to heat it up you can put cardboard in front of the rad and watch it.

a trick is to squeeze the top hose, you may notice that affects the water level in the reservoir differently when the thermostat is open as opposed to closed. doing that may help you decide when its open. If you like you can remove the thermostat, put it in water with a thermometer and watch it open, or just replace it. I'd have a look around that thermostat housing too to check for leaks.. usually the thermostat has a rubber seal around it's rim, they can rot out.

i was just doing the head gasket on my volvo and found that where the thermostat fits the aluminum head , it was a bit pitted. I cleaned it up well, and put a thin coating of JB weld, Ill flatten it back down to the base metal next and just leave the JB weld in the indents, it should be ok. I found in that car that the head gasket had gone between the combustion chamber and the waterjacket sending water out the tailpipe. It wan't warped. I flattened / cleaned it with glass and fine sandpaper and got it as best I could , filled some minor imperfections with JB weld and sanded off any above the surface.. I didn't feel like sending it for machining or want the head to have higher compression, it was already planed a bit thinner last time ( 20 years ago)

on my 944 I havent done lots yet except learning. I did buy a new top and bottom hose and the funny shaped hose molded to the bottle. It makes a bunch of weird bends and is about 3 feet long or so. Hoping I got the right hose.. I ended up with Dayco brand ones, at a not bad price. I noticed a huge variation in pricing so I'd look around. I didn't go for silicone hoses but there are some kits that have brightly colored ones in the form of a kit , including some others, as well as OEM.


any 35 year old hose is pretty much unreliable now so I'd do those if they have not been changed yet. You don't want a blown rad hose to fail out on the highway.