I am looking at buying a 1998 BMW 740i. When I got done test driving it I opened the hood and smelled coolant that went away in a few moments. From what I’ve read is the expansion tank has a pressure valve that may blow off to release pressure. Is it possible that this is what I smelled? Have seen no other evidence of a leak and the car did not overheat. I want to buy this car but don’t want to have expensive problems from the start.
The two most important words are prepurchase inspection
You read incorrectly. The expansion tank does not have any type of valve to release pressure. If you smell coolant, you probably have a leak. The cooling systems of those vehicles is the weak link. Like jclausen said, a pre-purchase inspection at a BMW specific shop or dealership will tell you what you're getting into.
ASE and BMW Master Certified Technician
I'm reluctant to disagree with someone whose listing says they are a BMW Level 1 Master Tech, but my understanding is that the expansion tank cap in the e38 DOES have a pressure release valve and a return valve. So it will let excess pressure out, air or coolant, and it will let air back in as needed when it cools.
Still, it is unlikely that the cap would let coolant out, or much smell, unless the system was too full of coolant. It's more likely that there's a leak somewhere. That can be real minor, or the sign of something significant. I agree, having the car checked out by someone who knows these cars makes sense.
- - - Updated - - -
Also, there's a section on this forum specifically for that model (the e38 740). That's the best place to post questions and read about issues/fixes for that car in particular.
Last edited by R Shaffner; 03-01-2019 at 07:33 AM.
You might want to go to that section, list some details about the car, and ask what are the key things to look for.
I'm pretty sure people will say to:
1) See if the timing chain guides have been replaced. These always wear out after 150,000-200,000 miles. Replacing them is a common requirement, unless they've already been done, and pretty expensive ($1,500 or so, unless you do it yourself -- then it's a few hundred and 2 days of work).
2) See how the cooling system looks. Many plastic parts. But that's not where the big $$$ items are.
And of course, to make sure the engine, transmission, etc. are running well.
Good luck!
You misunderstood me. The radiator cap is capable of releasing excess pressure. The CAP! Not the expansion tank as the original poster stated. There is no valve or anything on the tank. It is nothing but a plastic tank. The cooling system is pressurized to raise the boiling point. The pressure in the system will absolutely NOT go higher than what the cap can hold unless either the cap is bad (unlikely, but it can happen), or the vehicle overheats, and the pressure in the system exceeds what the cap is rated to hold.
It is not designed to simply release pressure and allow air in, under normal circumstances. It's just like the safety valve on a hot water heater. It should never vent unless there's an issue.
ASE and BMW Master Certified Technician
An early warning of a seeping head gasket is a venting cap, with odor,and no visible leak, the odor can also be in the exhaust.
Thank you all for your advice. I looked back and what I read was what I thought...that the expansion tank cap had a release valve. However I did see one on the 98 I was looking at. Anyway, I passed the car up because they would not budge on the price. There also appeared to be a potential power steering issue as it was tough to steer.
So I ended up taking a chance on an 04 745i with some minor but hopefuly easily taken care of.
One of the posts mentioned a useful forum for those models, does that include the 745? Im very new to BMW and German cars period other than a 72 Beetle. Im excited yet nervous.
Yep. Here it is:
https://www.bimmerforums.com/forum/f...2008-(E65-E66)
Congrats on the purchase. Good luck!
You got an 04 745? You must be a glutton for punishment. Did you do any research at all? The early E65/66 is easily and by far the worst BMW ever built. Good luck!
Sent from my Pixel XL using Tapatalk
ASE and BMW Master Certified Technician
If you smell coolant you DO have a leak. The source and severity will be the issue.
time to grill the seller
If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue
Bookmarks