Coolant leaking through reservoir cap, need new cap? - Alfa Romeo Bulletin Board & Forums
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post #1 of 19 (permalink) Old 06-16-2019, 03:46 PM Thread Starter
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Coolant leaking through reservoir cap, need new cap?

Hello Alfisti. I am a new member, and I am having some trouble with the cooling system on my Milano.

Overview:

The problem only seems to happen after the car has been run for a while at temperature. The easiest way to recreate the problem is to run the car on the highway for a while, then pull off and idle (usually I'm stopped in traffic). There will be a temperature spike, although it won't reach the red line. Then after I get the car moving again, it slowly cools down, but it's now leaking coolant through the cap. Usually by the time I reach my destination (another 10 minutes or so, mostly uphill) the float sensor on the coolant reservoir has tripped.

I have a few original Alfa coolant caps, but I don't trust any of them. I'm told I should use 0.7 bar cap, but I don't know where to get one. Also, I don't have the ability to pressure test the caps -- my mechanic has unfortunately lost his adapter. I've done a fair amount of reading on these boards and I know that the new made caps can be questionable.

Does any one know where I can get a trustworthy reservoir cap, and/or an adapter to pressure test these caps? I am worried the problem might be more serious, but I would like to eliminate the cap as an issue first.

The details:

1987 Alfa Romeo Milano, 2.5L V6 (Silver). My father bought it new, and I've been driving it for many years now. It has over 240,000 miles on it. It is a daily driver. When the engine needed an overhaul a few years ago, the mechanic instead replaced the engine with another one (still 2.5L) which had fewer miles. I've also had the transmission rebuilt. Next on my list of major overhauls is the exhaust, as it has lots of little leaks. However, this cooling problem has forced me to delay that.

The problem was first noticed a couple of weeks ago on a short trip out of town. It lost coolant through the cap after some hard driving. I initially thought the coolant reservoir had gone bad -- a problem I have seen before -- but after replacing it with an original tank I realized the coolant was escaping through the cap and not a leak in the tank. Around the same time my job changed office locations, and I now had a longer drive. So I was encountering this problem everyday on the drive home. At least once the car ran very hot (at the red line but not over it), and the coolant tank was empty by the time I made it home.

I arranged to take the car to the mechanic to have him do a thorough check up of the cooling system. He discovered that the thermostat was stuck open (which would explain why the car took so long to warm up), and replaced it with a 164 thermostat. He also replaced the radiator! However, he used a radiator from a three liter Verde. Now the car warms up in a reasonable time, and runs at a much better temperature than it ever did. However, the next day, after some hard driving it again bled coolant through the cap. *sigh* Now believing it was the cap, I rummaged around the garage and managed to dig up an old 0.7 bar cap. We couldn't properly test it, but it appeared to be the best of the lot. The next day it made the afternoon commute alright so I figured I could take it on a short road trip.

I had to travel about 150 miles, mostly along an interstate, to get to my destination. Before starting I checked the coolant levels and made sure the tank was filled to the seam, or just slightly over. The car was fine on the outward trip. The temperature was perfect -- it used to never drive this consistently, I am really liking this new radiator -- and it didn't appear to have leaked any coolant. The car then sat for about 7 hours, cooled down completely, and the coolant level still looked good. On the return trip, the temperature was fine on the highway. But the moment I got off the highway, and idled at a light, the temperature spiked. Once I got it going again, it cooled down, but sure enough, as I arrived at my destination the coolant level warning light came on, and it had leaked down through the cap.

The "other" cap:
When I went searching for that old 0.7 bar cap, I also found a Saab cap that my mechanic had given me a few years ago. It fits the Milano coolant tank, but I remembered it was of a higher pressure. I did some researching online and I think the cap should be 15 psi (slightly more than 1 bar). It's in almost unused condition, and I know that Alfa did make 1 bar caps for the Milano, so I decided to try it. Actually, I first tried it a couple of days ago. It didn't leak, but the increased pressure caused the small hose that runs from the top corner of radiator to the front of the coolant tank (the radiator overflow hose?) to leak at the radiator. Loosening the cap and relieving some pressure stopped the leak, but I decided to replace the hose anyway. However, the next morning I took the car to mechanic to have the AC charged, and he thought the 0.7 bar cap would be better.

After yesterday, I decided to try the Saab cap again. So I filled up the reservoir, put the cap on and let the engine warm up for 15-20 minutes. I then ran some errands around town, which gave me the opportunity to stop and check the cap frequently. The cap never leaked -- after about an hour the coolant tank looked like it was starting to bulge! To its credit, the tank didn't leak either. Eventually the lower radiator hose started to slowly leak at the t-junction, so I very carefully loosened the cap just a little to relieve the pressure, then made the short trip home. I strongly suspect that the Saab cap holds more than 1 bar of pressure! I'm *not* going to use it again.

Observations:

1. The problem takes a long time to present, which makes it difficult for the mechanic to see it.
2. At first everything appears normal. As the engine warms up, the coolant level in the tank rises, the thermostat opens, the fan turns on. However, eventually, as it continues to cycle, the coolant level in the tank appears to drop. I haven't really studied it before, but is that expected?
3. The radiator overflow hose(?) stays cool for a long time, even after the thermostat has opened. However, the other small hose at the top of the coolant tank -- the one that runs to the t-junction behind the engine, and links up with the heater -- gets hot quickly.

I apologize for the long post, I just wanted to be as complete as possible. If anybody has any ideas, it would be greatly appreciated.

Last edited by cplMilano; 06-16-2019 at 03:50 PM. Reason: grammar
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post #2 of 19 (permalink) Old 06-16-2019, 07:54 PM
Del
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If nothing else, I will say that from personal experience, the 2.5L engine radiator is marginal at best. Our 89 Milano overheated in hot stop and go driving, and changing the OE 2.5L radiator with the larger 3.0 L Verde radiator solved that problem. The inadequate OE radiator causing overheating can cause a good cap to leak hot expanded coolant.

Had that happen once in my 91S, after stopping at a gas station after a long high speed drive in 105F weather. The tank had been too full, and it spewed some coolant after the stop and the resultant coolant heating up even more.

Del

Seattle

1989 Milano, Shankle Sport
1991 164S, stock
1994 164LS (~Q)
1972 Morgan 27

previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
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post #3 of 19 (permalink) Old 06-16-2019, 08:38 PM Thread Starter
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Quote:
Originally Posted by Del View Post
If nothing else, I will say that from personal experience, the 2.5L engine radiator is marginal at best. Our 89 Milano overheated in hot stop and go driving, and changing the OE 2.5L radiator with the larger 3.0 L Verde radiator solved that problem. The inadequate OE radiator causing overheating can cause a good cap to leak hot expanded coolant.

Had that happen once in my 91S, after stopping at a gas station after a long high speed drive in 105F weather. The tank had been too full, and it spewed some coolant after the stop and the resultant coolant heating up even more.
I've only been driving with the radiator from the 3L Milano for a few days now, but I immediately noticed a difference. It runs cooler and more consistent. Even when the temperature spikes, it doesn't go as high, and it comes down more easily. The thought "where has this radiator been all my life" crossed my mind. :-)

However, it's still loosing coolant, and that's frustrating. It would happen in the past, especially when I put too much coolant in the tank, but not as severely. The fact that it started doing this before the radiator change, and has continued after it, means the radiator wasn't the culprit. I want to figure out this problem so I can enjoy the new radiator (and AC) this summer! ;-)
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post #4 of 19 (permalink) Old 06-16-2019, 09:20 PM
Del
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My feeling is that the OE Milano tank should be ok using a 1 Bar (15 psi) cap, as used in the 164 and most other cars, etc, but the Milano aftermarket tanks should probably use the .7 Bar cap to avoid damage to the tank. Same for the aftermarket tank in the 164. These aftermarket tanks are not as well built.

If you have an OE tank, I would use the 1 Bar cap since it seems to work, according to what you report. It's what we use in our Milano, and I've not had to change the tank (although I do have a coupler of spares, lol). I would be surprised if the SAAB cap wasn't 1 Bar, as that is industry-wide.

That, and tighten all the clamps holding the system together.

BTW, I understand that the Verde radiator is the only one available now, the other being a loser.

Del

Seattle

1989 Milano, Shankle Sport
1991 164S, stock
1994 164LS (~Q)
1972 Morgan 27

previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
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post #5 of 19 (permalink) Old 06-21-2019, 10:41 AM
vml
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You didn’t mention the water pump and it might get be that is not flowing enough at low rpm’s to remove coolant from hot spots. Also it’s possible that the engine has some deposits inside the block that might create a hot spot that only surfaces after the engine is hot and at low rpms. A simple experiment would be to use redline water wetter, which improve the contact of the coolant with the engine.
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post #6 of 19 (permalink) Old 06-21-2019, 10:48 AM
Del
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Possible, something to consider, but he did say that using the 1 BAR cap seemed to solve the problem, if I read his posts correctly. That and using the superior Verde radiator. I could believe that using the lower pressure cap and the inadequate Silver/Gold radiator could cause the problems he related, based on our own experience with our 89 Gold.

Del

Seattle

1989 Milano, Shankle Sport
1991 164S, stock
1994 164LS (~Q)
1972 Morgan 27

previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
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post #7 of 19 (permalink) Old 06-21-2019, 11:50 AM
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If even with new 3.oL radiator and 1 bar 164 cap you are still loosing coolant through coolant tan 164 cap coiple things come to mind:

1. Is cooling fan working correctly? This is also a simple wiring mode you can do at terminal board near air cleaner to keep fan running during heat rise after shutting down engine so thermal switch in radiator keeps fan running during cool down.

2. Test coolant switch on kitchen stove in water pot with ohm meter and cooking thermometer in the boiling water to see when switch makes.


3. Another possibility to check out is a leaking head gasket at a cylinder flame ring in head gasket putting exhaust gases into coolant system. I had a 2.5L Gold do that to me.

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post #8 of 19 (permalink) Old 06-21-2019, 03:49 PM Thread Starter
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Thanks for the responses.

The SAAB cap that I used didn't leak, although the coolant tank looks swollen after a while, and it did cause a mild leak in the lower radiator hose (I've tried tightening the connections). I believe that it s a 1 BAR (or so) cap. The coolant tank is original, but it is showing stress marks, so I'm worried how long it will last running that cap.

I am planning on ordering a 164 cap, and hoping for the best. I have no way of testing the pressure on any of these caps. I'm pretty confident my original 0.7 bar cap is not holding 0.7 bar any more. It is holding some pressure. Maybe an hour after I drive the car, I can unscrew the cap and hear it hiss off a little pressure. Whereas with the SAAB cap it retains pressure for many hours after some decent highway driving.

RE: Cooling fan:

The cooling fan, for the most part, appears to function correctly. Sometimes it seems to come on late (i.e. at a higher temperature). I have fitted an override switch, so I can turn the fan on manually, but since upgrading to the Verde radiator I rarely need to use it. When really hot (like it's been lately), and after a lot of stop and go traffic, it does have trouble with the temperature running on the high side. However, I still haven't seen it overheat, since going to the new radiator.

RE: Head gasket:

This is something I'm worried about, although I'm not familiar with this problem. So far I've seen no white crud under the oil cap, or white smoke. (I realize that failures in different places can cause different effects) Also, the engine has to get hot, go through a few cycles, and generally just be driven for a while, before the pressure in the coolant tank gets high enough to cause the cap to release coolant. Would a head gasket need to heat up like that?

Also, the SAAB cap doesn't leak. I would imagine that the pressures from a head gasket leak should be enough to get it to open up.

Thanks again for the responses.
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post #9 of 19 (permalink) Old 06-21-2019, 06:06 PM
Del
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We have run the 1 BAR cap on our original OE tank in our 89 Milano with no problems from new, now with 100k miles. Yes, the tank will distort a little under pressure, after all, it is a plastic balloon, so to speak, ie, not rigid. I would suspect that things are ok at this point in time. If you are losing no coolant now, I would go with it for a while to see what happens.

Del

Seattle

1989 Milano, Shankle Sport
1991 164S, stock
1994 164LS (~Q)
1972 Morgan 27

previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
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post #10 of 19 (permalink) Old 06-21-2019, 10:42 PM
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I have two Milanos one 1988 Milano Verde purchased new in 1988, and one 1987 Milano Silver purchased from the original owner in early 1990s. I had problems with leaking coolant tanks and buy used Alfa coolant tanks because they do not leak. The tank leaks from return lines or from cracks in the tank. The reproduction tanks never seem to last more than six months. The Verde will sometimes run hot in bumper to bumper traffic in very hot weather and had to turn off the AC. The Silver car never runs hot even in hot bumper to bumper traffic. I had to replace the Verde radiator because it was cracked many years ago. I always carry radiator fan relays because they sometimes fail and your car will overheat. The Verde has 245K miles and the Silver has 110K miles. I like driving the Verde much more than the Silver model.

The head gasket fails when oil leaks into the coolant. I have replaced head gaskets with the Reinz head gaskets and stopped the oil leaks. I also rebuilt the Verde engine at 180K miles because I wanted to put 10:1 compression pistons and "S" cams. The engine did not have to be rebuilt.

I recently drove a Stelvio QV last Saturday and the power is truly amazing and really want to buy a Giulia QV Coupe. The Milanos are over thirty years old and need replacement.
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post #11 of 19 (permalink) Old 06-22-2019, 04:44 PM Thread Starter
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Originally Posted by kuni123456 View Post
I have two Milanos one 1988 Milano Verde purchased new in 1988, and one 1987 Milano Silver purchased from the original owner in early 1990s. I had problems with leaking coolant tanks and buy used Alfa coolant tanks because they do not leak. The tank leaks from return lines or from cracks in the tank. The reproduction tanks never seem to last more than six months. The Verde will sometimes run hot in bumper to bumper traffic in very hot weather and had to turn off the AC. The Silver car never runs hot even in hot bumper to bumper traffic. I had to replace the Verde radiator because it was cracked many years ago. I always carry radiator fan relays because they sometimes fail and your car will overheat. The Verde has 245K miles and the Silver has 110K miles. I like driving the Verde much more than the Silver model.

The head gasket fails when oil leaks into the coolant. I have replaced head gaskets with the Reinz head gaskets and stopped the oil leaks. I also rebuilt the Verde engine at 180K miles because I wanted to put 10:1 compression pistons and "S" cams. The engine did not have to be rebuilt.

I recently drove a Stelvio QV last Saturday and the power is truly amazing and really want to buy a Giulia QV Coupe. The Milanos are over thirty years old and need replacement.
I wish they would offer Giulia's with manual transmissions. I brought it up to the dealership and they told me they hear that a lot! ;-)

That's interesting that your Milano Silver never overheats -- even when new, this one would overheat or threaten to overheat after a time in stop and go traffic. All relevant parts that I can think of had at one time been replaced -- the only thing to make a difference seems to be the recent installation of the Verde radiator.

----------

I tried running the car with Saab cap again, and, from what I can tell, it leaked a little from the lower radiator hose, but only a little. The tank swelled up (a lot), and eventually the coolant level in the reservoir dropped very low. Carefully loosening the cap to relieve pressure, eventually the coolant level bubbled back up to about the middle of the tank. After cooling off, the level was a little low again this morning. I don't know what's going on, but that seems like it's holding too much pressure?

I ordered a 1.0 bar coolant cap from centerline. I also have a contact in Italy who works for a fiat dealership, and said he sometimes comes across parts for old Alfas, so I asked him about a 0.7 bar cap. :-) I'll see what he turns up.
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post #12 of 19 (permalink) Old 06-29-2019, 03:14 PM Thread Starter
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More developments:

Monday I noticed a burnt smell in the coolant reservoir and on the coolant cap. I wondered if I did have exhaust gasses in the coolant, and I became worried I have a leaking head gasket, or a cracked cylinder head. The mechanic inspected the car on Thursday, including opening up the coolant tank and revving the engine up (I assume looking for bubbles). He doesn't appear to be too concerned, stating that there should be other symptoms if there was a leaking head gasket or cracked cylinder head.

The new 1 bar cap arrived on Wednesday -- I can now confirm that the SAAB cap is holding more than 1 bar of pressure. ;-) Unfortunately, the new cap also bleeds coolant. So the cooling system is still being over-pressurized. No other leaks are visible, just coolant coming out of the cap.

However, otherwise the car seems to be driving well. I've seen no white smoke. It is not overheating, although the last couple of days it may be running a bit hotter, but that could be due to the higher pressure cap. It's running well, getting good mileage, etc. In fact, other than blowing out coolant, the car is running as good as it ever has.

Is there anything else that could cause an overpressure like this? Or is it just in an early stage of head-gasket (or cylinder) failure and it's just a matter of time before more symptoms start to show?
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post #13 of 19 (permalink) Old 06-29-2019, 04:21 PM
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So here's the thing about the Milano: there is not enough head space in the expansion tank. If you fill it to the top mark, you will get coolant out of the cap when it gets hot even with a good cap.

The trick is basically to just fill it to the seam in the tank. This is enough so you don't get the low coolant warning, but leaves enough space in the tank for the coolant to fully expand.

Hopefully that's your problem. I'd also suggest sticking with the 0.8 bar cap.

Tom

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1974 GTV
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Former: 1987 Milano Gold
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post #14 of 19 (permalink) Old 06-29-2019, 04:53 PM Thread Starter
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Gubi:

I've been filling it minimally, just barely to the seam. Still losing coolant, so I think it's overpressurized.

kuni123456:

I received your PM, but I'm not allowed to respond to it, because I haven't made enough posts.

I've had problems with cracked reservoirs before, and I too have had trouble with the new reservoirs. I have managed to find a couple of good used reservoirs which is what I'm using now. Currently the reservoir will swell a little before the cap starts to release coolant. When I used the Saab cap, the tank would swell up a lot, and then usually leak from a hose.

The new cap is the kind with a spout, and when it leaks I can see coolant in the spout. I will keep an eye on the reservoir, because that Saab cap really stressed it, so eventually it may start to leak. But at the moment it appears that the cap is releasing pressure, not the tank.


Everybody:

Thanks again for your input. For almost the entire month I've had to add coolant everyday. I must admit I'm tired of it, and if I don't figure it out soon, I will be looking for another vehicle. I would just like to know what's causing it. So I really do appreciate all the feedback and offers to help.
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post #15 of 19 (permalink) Old 06-29-2019, 08:27 PM
Del
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Have you retorqued the heads? Any chocolate mousse under the oil filler cap? After many thousands of miles, these engines do need head retorques. Most don't do that simple chore, diving straight into gasket changes, when actually, the gasket is not faulty, just not held tight.

Let go, yes, it could end up being a problem, but it is better to be sure the head(s) are torqued to the design level first.

Del

Seattle

1989 Milano, Shankle Sport
1991 164S, stock
1994 164LS (~Q)
1972 Morgan 27

previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6

Last edited by Del; 06-30-2019 at 10:00 AM.
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