Hi guys, I have a 96 Jetta GL with an AAZ.
Lately my coolant temps have been all over the place. Last summer I noticed the temps starting to creep from 90* up to around 100*. I could shut the car off and on and immediately it would drop back to 90*.
Now, the car seems to be running mostly at 100* and can creep up a little above, then go back down to 95-100* or so. One time I even saw it jump quickly to 110 and then back down to 100* within 1-2 seconds.
I have yet to check whether the car is actually at these temperatures using an infrared thermometer.
I just replaced a leaking lower 3-end coolant hose that is just above the outlet of the water pump and replaced with new coolant. The car also has a fairly new coolant bottle and radiator coolant sensor. I replaced the plug end for this sensor as it had melted and the fans never came on. Since replacing the sensor and plug from time to time the fans do come on but only for a few seconds at most. I do not hear them come on often though.
I ran the car for a while without the overflow tank cap on to remove any air bubbles so I don't believe their are any air bubbles still in the system.
Do you guys think it is a faulty engine coolant sensor or perhaps a bad thermostat? Where are either of these on this engine? I haven't looked too closely but cannot find any pictures or diagrams for this engine showing them either.
I say it is still some air. You have to get it hot enough to open the T stat to flush all the air out if it was in there to begin with. I would keep adding your coolant as needed. The T stat could be sticking as well.
Those fans usually never run more than a few seconds on all my diesels. Maybe someone else has a different experience?
I have had two cars with erratic temperatures that were both gauge related rather than sensor. Sudden changes seem electrical in nature rather than mechanical.
The last time I changed a thermostat. I was rewarded with 10°C less temperature. The old one was opening at higher temperature than it should have.
Lots of bubbles persistently on a hot engine can mean that it may have a head gasket fault.
Sorry, I failed to mention a few things.
I had been adding coolant over the next few days after the coolant change as usual when doing coolant changes to remove the bubbles so I am fairly sure that all bubbles should be gone however I will check again.
Also, it seems the temps stay around 90* C or slightly above when driving around town. It stays around 100*C and moves slightly above and below as the T-stat opens when on the freeway. It is also quite cool out right now, i'd say around -10*C ambient temperature so I don't see why it's heating up on the highway. I do not have the rad blocked.
plugged rad? Bad pump?
Today with the gauge just above 90* at a stoplight the fans came on for about 5 seconds.
Also, when I got the car the one coolant hose coming off the oil filter housing (I assume for oil cooling) was blocked off. The one hose coming off of it has a plug in it. Not sure where it is supposed to connect to. However, the car has always been that way since I've had it with no ill effects so I don't see that being the issue.
I have not yet checked the small line going back to the reservoir, apparently their is some sort of restrictor in there?
If it is the t-stat where is it located on this engine? I read that all the coolant will have to be drained (or will drain) when I remove it so it leads me to believe it's down low on the block. That sucks.
Sounds like you may need to spend some time sorting things out.
If the fluid is recent and you want to recycle it, catch it in a pan and then refill a jug with it with a funnel with a strainer in it.
You are going to be in trouble in warmer weather if your gauge is accurate.
Install an additional mechanical coolant gauge to verify your temps.
Do you have any black film, high pressure or little bubbles in your coolant reservoir?
Any restrictions in front of your radiator?
Any leaks around the mating surface of the head and block?
Is your coolant cap good? I've had brand new caps that were bad.