Leaky rad cap?

[DaveVoorhis]

Could somebody do me a favour? With your car parked somewhere silent and your engine cold, put your ear up to the rad cap and give a rad hose a squeeze. Do you hear a hissing from the rad cap as air is released? Mine hisses when I do this, but I don't think I'm squeezing up enough pressure to hiss out a properly working cap. I've got a slow coolant loss and the engine is slow to warm up, and the temp gauge normally runs well below the half-way mark. My previous 525i always ran just a hair below the half-way mark. Maybe a bad rad cap?

Initially, I assumed the coolant was disapparing via a leaky heater core, so I opened it up tonight but the heater ducts are dry and the visible side of the core is clean. Yet, a previous owner jammed paper towels all around the edges of the console (I'm assuming this was to catch drips) and the windscreen was slightly greasy. Is it a common failure mode for the core to leak so slowly and produce such a fine mist that everything looks fine?

Having gone to the considerable effort of opening everything up (short instructions for accessing heater core: disassemble car), I'm half inclined to replace the core -- even if it's good -- just as preventative maintenance.

[632 Regal]

4 hours and mine is still warm with pressure... I really dont think you should hear anything when squeezing the hose. maybe the previous owner messed with the cap so you dont get pressure and the heatercore dont leak.

our cars are well known for slow heatercore leaks.

even with no pressure it should run in the middle of the temp gage, bet your thermostat is fubared if there even is one in there. your engine will have tremendous wear when running cold!

forget everything else right now and fix the thermostat.

[DaveVoorhis]

My rad cap was definitely bad, not messed with as far as I can tell, but bad. I forgot I had a spare on an old rad in my shed. I put it on, and there's no hissing from the cap when I squeeze the hose.

I idled the car until it warmed up and the gauge shows just under centre -- about the same as where my last 525i ran, but I'm gonna replace the thermostat because it seems to cool down from there when moving.

After idling, I inspected the cooling system and some coolant on the frame rail under the rad and under the bottom of the rad. It was cold, so I suspect it was coolant that previously drizzled down from the bad cap, but I'm going to wipe it down and run it again just to be sure.

The heater core, run in the open with the shroud off, showed no evidence of leaks.

[632 Regal]

hopefully it sealed up. Mine has a micro leak and defrost dont work in the rain unless I hit the AC button.

The heater core, run in the open with the shroud off, showed no evidence of leaks.

[DaveVoorhis]

I couldn't find the slightest evidence of the core leaking. All the ducting was perfectly clean, and I ran it for a long time with the heat full on and the car closed up. There was no smell of antifreeze. I examined the stuff that was crammed around the edges of the console; what I first thought was wadded-up paper towel. It isn't. It's a two-ply tissue paper of some sort, kind of like toilet paper but thinner, continuous, and obviously cut from a large sheet. It's useless for absorbing water, and there are no water marks or any indication that it's ever been wet. It also ran the full length of the console, way beyond where any coolant would leak.

Bizarre.

I guess the final test will be the next cool, rainy day. If it fogs up and the defroster won't clear it... When my last E34 popped the heater core, it was obvious. A few weeks of driving around with the windows continuously fogged, followed by coolant drizzling down the carpets.

I noticed the rubber donut around the shifter was displaced and partly stuffed down the hole, possibly allowing outside air to come up under the console. Maybe the tissue paper was in there to block drafts???

The rad turns out to have a very slow leak when cold, so that and the bad rad cap explain the missing coolant.

[ryan roopnarine]

did you button the car back up yet? if you haven't, take the core to a radiator repair shop and have them test for leaks--that is, if you are reusing the same core.

[DaveVoorhis]

The dash is back sealed up like a, uh, sealed up thing, since I need to use the car this weekend. If the core is leaking, I'm sure I'll know it soon enough.