P1296 Code and lessons learned

[cep]

Recently took daughter's '02 NB to shop to diagnose an airbag light. Though the MIL light was not on, the shop's VAG-COM also found a code which was 'cooling system fault', caused by a bad thermostat or coolant temp sensor.

I'd already replaced the coolant temp sensor a couple of years ago, so figured the thermostat was stuck open. The shop wanted $160 to replace the thermostat (from my point of view now, that would be a bargain). For various reasons, I did not take them up on that. A few days later, the MIL came on and my OBDII reader found a P1296 code, the same thing as the shop found with VAG-COM.

I accumulated what I thought were the necessary parts, a thermostat and o-ring. Armed with this how-to http://forums.audiworld.com/tt/msgs/1304805.phtml, I dug in yesterday.

The first thing to be destroyed, as predicted in the link, was the oil dipstick tube. Broke as if made of vanilla wafers. The second thing to go wrong was that the removing the coolant line from the oil cooler, as per Bentley to drain the block, is impossible without removing both lines because they are both in a rubber-like tube which prevents one from moving unless the other does. Gave up on draining the block. I also had to take the air injection pump off just to have any hope at all of getting pliers on the clamp on this hose. In doing that, I broke one of the squeeze clamps on the inlet hose that runs from the air filter box to the pump. It looks to be integral with the hose, so I'm sure I'll have to buy the whole assembly.

Then, to top things off, when I removed the(plastic--be careful!) thermostat housing, no gush of coolant came because the thermostat was closed and doing a quite effective job of keeping coolant in the block. Since I couldn't drain the block, precious G12 went everywhere when the thermostat was removed. Oil dry to the rescue.

So, I was expecting to find a stuck-open thermostat but didn't. I even cooked it in a pan of water on the stove and it works fine. That only leaves the coolant temp sensor, so I guess I'll buy another one of those from the dealer tomorrow and install it. I'm still going to replace the thermostat but have no illusions about it being a part of the P1296 problem.

I really don't understand how the computer can diagnose a cooling system problem unless it has a pre-determined limit on how long it should take the engine to come to a certain temperature. If it takes too long, it throws a code?

[Smileybug]

Be sure you get the right temperature sensor. They came out with new ones, that I think the top will be green (mine was, but mine is a '99...not sure about color for the newer cars, someone else will have to chime in on this one). Those are the repaired ones. They seem to have known issues with the others but the green-top sensors are supposed to work properly now. Since you replaced it a few years ago, it might still be the incorrect one.

[cep]

Yes, I got a green coolant temp sensor. The one that was in it was green, too.

The reassembly was an unmitigated disaster. I noticed a small drippage of coolant when I refilled it, but deluded myself into thinking that these drips were coolant that was trapped in various places from the drenching that occurred when I removed the thermostat from the undrained block and had moved the car, thus disturbing their slumber. After all, the two side covers on the underside were still in place and I could see coolant on them.

Big mistake.

I went for a short drive to warm it up and promptly the overheat light came on. I stopped, raised the hood, and coolant was everywhere. I was only a little more than a mile from home, so I let it cool off a little and drove it home. The outside temperature was, and has continued to be, 10F or less and when I got home the engine didn't seem hot--no steam to speak of.

I parked it in the yard to let it drip in the grass. I had every intention of calling a tow truck and just hauling it to a shop and be done with it.

However, stupidity trumped common sense once again. Determined to find out what I did wrong, this morning, with an invigorating +2F outside air temp to work in, I started the autopsy. Fully expecting to find a pinched o-ring on the thermostat housing, I thought, "How cold could I get? It's only one hose and two bolts." And it didn't take long. But...the o-ring looked fine.

WTF,O? The only places I messed with that could leak were the t-stat housing, the coolant temp sensor, and the drain plug on the radiator. I tried to get one hose off the oil cooler, but couldn't. The timing belt end of the engine seems to be the most drenched with coolant.

Is it possible...that the water pump let go? That would be my luck. But...it was fine prior to me messing with the t-stat.

[05yellowbeetle]

How many miles does the beetle have?

The water pump on my '98 went at 60K. If you let it run and it overheats in under 5 minutes, the water pump is gone. Been there, done that, a rather fun weekend.

[cep]

It has 77K.

If it is the water pump, this would have to be the weirdest coincidence I've ever experienced. There were NO leaks on this car prior to my tinkering with the thermostat. For the water pump to fail while it was being worked on for something else would truly be remarkable.

It would, however, be my luck.

[05yellowbeetle]

cep, whether or not the water pump is currently broken, I would change it ASAP. I've never been more frustrated & worried at the same time as when the water pump broke on my beetle. I did most of the work on that beetle with help from my dad and brothers, but that day I was truly upset & nervous at the prospect of not being able to drive it home. Luckily, I made it most of the way, the pump went out about 12 miles from home in May in S FL, my brothers towed it the last 3 miles home, we though initially it was a hose or the thermostat. There was antifreeze on the passenger wheel well and on that side underneath as well if I remember correctly. I don't know how it ended up there, but it did. The beetle did smell hot and nothing seemed to help, but it was also 85-90* at the time.

I would not want your daughter going through that, so I'd get it changed now, if it hasn't already made the decision for you.

[cep]

Update: Car is finally up and running.

It wasn't the water pump, thank God.

Using the time-honored tradition of 'throwing parts at it', I finally fixed it. I figured that since the only place I'd been rooting around was the thermostat housing, the leak had to be there. So, Friday I went to a VW dealer and bought a new t-stat housing and o-ring. Saturday was a rainy and miserable so I didn't mess with it. Today, I took off the t-stat housing (this had to have been the fourth or fifth time). As usual, I could see nothing wrong with it.

Put on the new housing and o-ring, fully expecting it to have no effect whatsoever on the problem. But, to my surprise, it fixed the leak. I was flabbergasted. I examined the old housing under a good light and still cannot see anything wrong with it. I thought maybe I cracked it (it's plastic) when I was removing the radiator hose but don't think so. Maybe it was the o-ring but it looked good, too.

Anyway, with new t-stat and coolant temp sensor installed, I cleared the code. It will be interesting to see if this fixes the P1296 code or if it will recurr.

This car has always gotten poor fuel mileage. Hopefully, this will help that problem. I changed the oil at the same time and the oil had a smell which reminded me of my old 2-cycle go-cart engines--like there is a lot of gas in the oil. Also the oil filler cap bottom is covered with milky looking sludge which tells me there is a lot of water in the crankcase or at least there has been. I'm hoping that these two problems, along with the lousy mileage, are symptoms of an engine that has been running too cool. Too low of operating temperature would cause the computer to adjust the fuel/air mixture to a richer than normal condition. It might also never allow the engine to get warm enough to burn off the condensation in the crankcase.


Probably wishful thinking, though.

I agree that it is time for a new water pump. It is probably about time for a timing belt, too, and that would be a good time to do it. I don't think I'm up to that task. I'm like a bull in a china closet when it comes to working on these newer cars.