Coolant leaks galore w/ excessive pressure…

[RockJock]

The car: 1989 535i w/ about 183K miles

About 6 weeks ago the car developed a coolant leak around the water pump [6 year old water pump was shot and the short elbow hose that goes from the thermostat housing to the water pump had a pinhole].

A few weeks go by and she develops another leak: this time from the radiator vent return line [the pisser line; which flows nicely as it should] where it connects to the expansion tank. We replace that and everything appears to be okay for about a week or so. Then I notice a leak from the short elbow hose [new] along the hose clamp. I figure that it probably needs to seat itself and I proceed to tighten the clamp some more and everything appears to be okay. I take the car on a road trip and about 300 miles from home the upper rad hose blows [I was able to get the car to the side of the road and shutdown before the temp even got a chance to get more than a needle width past the ¾ mark].

The upper rad hose gets replaced along with the one that goes from the water pump to the expansion tank. Now all hoses [except the lower rad hose] are new. A few hours of driving and I’ve got more leaks; all of the leaks are coming from the hose clamp areas [where the upper rad hose connects to the rad, where the return hose goes into the bottom of the expansion tank, and the elbow hose connection into the water pump is leaking again].

I noticed that the cooling system holds pressure overnight. When I open the expansion tank cap I hear a hiss and the coolant level rises. Oil is nice and clean [no milkshake], and the coolant looks nice and clean. I just replaced the expansion tank cap [200] w/ a 140. We’ll see what gives.

The temp needle always sits about a needle width to the right of dead-center [w/ a brand new fan clutch]; I know many of the guys here are adamant that it must sit dead center…

Any ideas? Could this be a HG or cracked head issue? Should I get the cooling system checked for exhaust gases? Thanks guys.

[Mr._Graybeard]

Overnight cooling system pressure is a bad sign. A garage can test your coolant reservoir with an exhaust sniffer for the presence of hydrocarbons -- there's only one way for them to get there.

You might try a test a friend of mine showed me once, working on a 5-liter Mercedes. He dipped a pencil into the coolant in the overflow tank, pulled it out and held a lighter flame under it -- it lit like a candle!

[RockJock]

Overnight cooling system pressure is a bad sign. A garage can test your coolant reservoir with an exhaust sniffer for the presence of hydrocarbons -- there's only one way for them to get there.

You might try a test a friend of mine showed me once, working on a 5-liter Mercedes. He dipped a pencil into the coolant in the overflow tank, pulled it out and held a lighter flame under it -- it lit like a candle!

Thanks; that's what I'm thinking...I'll get someone to "sniff" the coolant...

Also, does anyone know how common it is for newly installed hoses to start leaking at their connections [i.e., from under their hose clamps]?

[SnakeyesTx]

They sell a dye that you can drop into your coolant. If it turns bright yellow, you've got a HG exhaust port pressurizing a water jacket. This is actually quite common with M50's. It's happened to me once, it's happened to several of friends of mine who bought not-to-well-maintained 525's and I've seen it several times on here.

In almost every instance, we had to get a replacement motor because even the deck of the block and head was warped enough to where most shops say "a used engine is cheaper than all the machine work needed."

[Kibokojoe]

It happened to me on a Honda Accord. Head gasket leaks will put a lot of pressure on the coolant system. I had hoses blowing and a radiator that sprung a leak before I figured it out.

[Tiger]

200 is way too high and BMW sells only 140 replacement. It can be because your old cap is not releasing pressure as it should.

[whiskychaser]

200 is way too high and BMW sells only 140 replacement. It can be because your old cap is not releasing pressure as it should.

+1
When I got the car about 5 years ago, BMW told me there was an outstanding recall on the rad cap. It had already been changed so they didnt give me a nice new one. Mine holds a bit of pressure overnight and the needle is half a needle's width to the right of 12 o'clock. It will go a year without topping up the oil or coolant. I'd be interested to know more about this dye though

[bimmo_2007]

200 is way too high and BMW sells only 140 replacement. It can be because your old cap is not releasing pressure as it should.

+1
Stuck valve of pressure cap would cause such a problem.

[RockJock]

***UPDATE***

Thanks for the tips guys….

I cleaned the coolant mess under the hood and installed fresh hose clamps on the leaky connections. Although I’m still getting some residual pressure w/ the 1.4 bar expansion tank cap it doesn’t seem to be nearly as significant as before. I’ll give it a few days to see what gives.

Here’s a snapshot of my temp gauge at operating temp [new fan clutch, new waterpump, thermostat is a few years old]. The temp gauge in my other E34 would always sit dead center except on really hot days [i.e., north of 30 deg C] in stop n’ go traffic [it would get a needle width to the right of center].

[Tiger]

How long after shutdown are we talking about for residual pressure?