slow coolant leak - mk4 12v VR6

[john]

I lose about 10-12 fluid oz of coolent every 5 weeks.  I keep a bottle of water in car because of it. 
I'm sure my 50/50 mix is now 95% water since this has been going on for half a year or more.  
I want to do a coolant flush but not before I find/fix my leak.


Where should I be looking?  I don't notice any residue around the reservoir, and my hoses appear fine.
It's a slow leak so I don't know that I would see something.

water pump?
I know on the 1.8T engine, the water pump has a flange or seal or something that wears out. 
I don't know if my engine uses the same pump, or where that pump would be.    
any help or ideas?

TIA

[vdubsunday]

Get some more coolant in there so the residue shows up better. I think your pump is by the crank and power steering pulley.

[john]

that would make sense.. that's where the belt is

[cryption]

start with coolant bottle and hoses.  Look for residual water

[Zach]

The water pump on the 12v is not something that owners don't need to be concerned about. It's not one of the common replacement items because it just doesn't go out really. I pretty much overhauled my entire coolant system, but left the waterpump untouched. IMO putting in a new one would make it more prone to future leaks where it seals.

The fact that it's that slow of a leak means that it probably isn't leaking at idle. Remember that the pump is driven by the accessory belt - so flow and pressure inside the coolant system is directly related to engine speed. If you want to find the leak you're going to need two people. Get the engine up to temp then have someone rev and hold the engine around 4-5k rpm while you snoop around the bay and look from under the car. We found leaks on Will's car that were otherwise unnoticeable by using this method.

Check the radiator, the thermostat housing, crack pipe, where the main hoses connect to the radiator, coolant reservoir. There may be some spots you can't see which you'll just have to feel for wetness.

[john]

The water pump on the 12v is not something that owners don't need to be concerned about. It's not one of the common replacement items because it just doesn't go out really. I pretty much overhauled my entire coolant system, but left the waterpump untouched. IMO putting in a new one would make it more prone to future leaks where it seals.

The fact that it's that slow of a leak means that it probably isn't leaking at idle. Remember that the pump is driven by the accessory belt - so flow and pressure inside the coolant system is directly related to engine speed. If you want to find the leak you're going to need two people. Get the engine up to temp then have someone rev and hold the engine around 4-5k rpm while you snoop around the bay and look from under the car. We found leaks on Will's car that were otherwise unnoticeable by using this method.

Check the radiator, the thermostat housing, crack pipe, where the main hoses connect to the radiator, coolant reservoir. There may be some spots you can't see which you'll just have to feel for wetness.

Good info..  I get what you ment by your context.  But I think you just added an un-needed "don't" here, right?
I'll get some help and snoop around after I do my oil change since I'll be under the car anyway. 

[Zach]

Nah, that's intentional. It's not a common failing part at all. The 12v engines have a reputation for bad and often failing cooling systems, but the water pump itself is least failing part. Pretty much every other part will have to be replaced before it goes. It's a fairly easy part to replace, but I wouldn't touch it unless the leak you're talking about is coming from where the pump seals against it's cup in the block.

As I said, putting in a new one would only make a leak more likely in the future.

[FortySix]

Nah, that's intentional. It's not a common failing part at all. The 12v engines have a reputation for bad and often failing cooling systems, but the water pump itself is least failing part. Pretty much every other part will have to be replaced before it goes. It's a fairly easy part to replace, but I wouldn't touch it unless the leak you're talking about is coming from where the pump seals against it's cup in the block.

As I said, putting in a new one would only make a leak more likely in the future.

Well I agree with you there, but that doesn't mean that it is not of concern.  The water pump being the least likely cooling system part to fail doesn't mean much when you consider how likely other parts are to fail.  Many of the other coolant system components will break fairly quickly during the life of the vehicle, leaving the waterpump due to be changed.  When the plastic impeller blades break they can lodge downstream of the pump complicating the repair.  Also on MKIVs, replacing the waterpump is not very simple (not as simple as on MKIIIs I think).  Most people replace it with a metal impeller water pump when they do chains b/c the engine usually has to come out for both.  But I don't think that is John's problem as they don't tend to leak, but the blades break, clog the system and cause an overheat.

As for John's problem, the most common areas on the MKIV are the t-stat housing and the crackpipe.  I know I have already replaced both of mine and my car has 95K miles on it.  I would try to look at the engine bay from above and below for a white-pink chalky residue.  That will help you ID the area of the leak.  I know I carry a bottle of 50/50 in my trunk at all times (it fits perfectly in the stock CD changer location in my Jetta 

[SixPack]

go to a shop, they will charge half an hour ($45) to do a pressure test, and tell you exactly where its leaking from. thats only if you cant find it.

[2k2golf]

check your coolant hose flange

[Spenis]

Metal T fitting time. Check the hose closest to the radiator. Or show up to the BBQ and I'll show you more then likely where your leak is (or the most common places where it does).

[john]

Wow..  thanks for all the help so far, guys! 
I have almost 140k on this engine, and I only had one other coolant issue. 
My radiator hose busted around 60k miles.

I'll def check out the thermostat and crack pipe.  I should be able to find them. 

[SixPack]

Wow..  thanks for all the help so far, guys! 
I have almost 140k on this engine, and I only had one other coolant issue. 
My radiator hose busted around 60k miles.

I'll def check out the thermostat and crack pipe.  I should be able to find them. 

yea if you never changed the crack pipe, then that might be it too... mine went out and 105K. gotta take the whole front end off though 

[john]

I'm not a little guy.. pretty much any parts swapping under the hood starts with taking the bumper off.  It just makes things easier and gives me more room to work.
It's one thing I def know how to do.   

[Will]

youre lucky thats the only problem you've had with coolant leaks thus far. 10-12 ounces every five weeks is not bad at all.
another source of the problem that no body mentioned is your coolant cap. the pressure mechanism under the cap can bust and let coolant leak out of the top. you should be able to see coolant build up in this area if this is the case.

could also be a small leak in you radiator, hopefully not. radiators are expensive 

[SixPack]

I'm not a little guy.. pretty much any parts swapping under the hood starts with taking the bumper off.  It just makes things easier and gives me more room to work.
It's one thing I def know how to do.   

yea most people complain about it. i dont have most of the bolts in on my front end so it takes about 6 minutes to take the whole thing off 

[john]

I don't think I have all the bolts in either.  I had extra the last few times I took off the bumper and couldn't find where they went.   

[john]

If my "crack pipe" is leaking, what should I replace it with.  My regular online suppliers (MJM and parts4vw) don't show "crack pipes" in their inventory.   
The DIY bellow lists a company that makes a metal one, but I dont know the company. 
I did find the OE one though..  http://www.parts4vws.com/catalog/product_detail.asp?PartNumber=021121050C



DIY for my reference..
http://www.gruvenparts.com/website/diys/crack%20pipe%20installation.htm

[FortySix]

I have the gruvenparts in my VR6.  The quality is outstanding.  Several companies manufacture a metal one (like MasonTech), but IMHO gruvenparts has the best one.

FYI I think the part is technically known as the "coolant distribution pipe"

[john]

ok..  I guess I wanted to make sure they were a real company.

[FortySix]

They are most definitely a real company making really innovative and needed parts for the vw community, esp. VR6s.

[john]

still haven't gotten under the car to check things out..  the cold wettness today made me lazy

Today I noticed my coolent resivor lid did not have an o-ring on it.  I thought it use to. 
It should have one, right? 
It would be nice if that's all it is.  That's an easy fix.

[SixPack]

well there should be an O ring, yes. and if its leaking from that, which it could, then you will see all the dried up coolant anyway. if thats not it, then its probably the crac pipe or the bomba de aqua.

[Buddy Lee]

John, the o-ring is on the smaller round sealing cap under the cap, it moves around. The o-ring fits in the opening of the coolant bottle.