My Jetta started to overheat on Friday. I’ve since changed the expansion tank, the radiator and the thermostat. It idles fine, but once I start to rev the engine it overheats. When I stop revving the engine the temperature comes back to normal.
I’ve noticed the only one of the fans on the radiator assembly is coming on, also, the bottom hose on the radiator, the one closer to the thermostat, is taking along time to get hot. The car normally runs at about 190F. After looking into some other illustrations it appears that the cooling system on this car operates in reverse, as far as the coolant flowing through the engine.
It is possible that the head gasket is breached. Carefully check the old expansion tank and the dipstick for signs of oil intrusion into the cooling system, and coolant intrusion into the crankcase. While this is not a strong possibility, the possibility of engine damage from a breached head gasket should make this the first priority to check.
Even though you replaced the thermostat, there is the possibility that it was installed backwards. On some cars this is possible, but I don’t know if that applies to VW engines.
The impellers on the water pump could be eroded, and thus, not able to push as much coolant through the system as should be taking place.
I know the T’STAT is installed correctly, and i verified that it works before i installed it.
Any thoughts on why only one of the fans come on. Even when I turn on the AC the main fan just goes to high speed, nothing from the second fan.
I am really hoping it’s not the water pump, but i was definitely thinking that it may be that. Are there any signs, other than the overheating, that the water pump is defective?
Based on what you wrote, “I’ve noticed the only one of the fans on the radiator assembly is coming on”, I assumed that the radiator had only one fan, and that it is working properly. Now, it appears that you meant to tell us “that only one of the fans is working”.
Based on that new interpretation, I would suggest that you check the fan relay and the engine’s temperature sensor. More than likely the relay is the problem.
I’ve read somewhere that if the upper hose becomes hot then the problem is not with the water pump as water is flowing through the system. I just don’t understand why the bottom hose is cold.
Does the flow go from bottom to top or top to bottom?
Update…the fan motor is bad, went to Pep boys and got a replacement and it does not fit my car. Ordered one online and should be receiving it on Wednesday. Not sure yet if that is the problem…BTW no signs of oil or coolant where it shouldn’t be, so I am ruling out the head gasket…will update as it develops…
The bottom hose should get warm shortly after the top one does, and they should be within a few degrees of each other once the engine gets to temp, at least with a gas engine. Diesels can be cold-blooded.
How much heat do you get from the heater?
The bad fan motor should only cause a problem in stop-and-go driving. If it was overheating over 50mph you have other problems. Air flow from the motion of the car should take over around there.
If you mixed VW and other coolant, or refilled with non VW coolant you may have sand precipitate or goo in your system now. You need to fully flush the system, and should always flush it when changing coolant types.
It you have changed the radiator and thermostat, and correctly, then there are still a few things to check. 1. Replace the radiator cap–if it’s not pressurizing correctly that could be the prob. 2. Check the relay for the fan that isn’t turning on, then check the fan itself. 3. Look for sludge in the system, but that should be easy to see in the overfill tank or radiator (before you changed them.)
HOWEVER… Because you said that it happens when you rev and that the bottom hose is taking a while to heat up, I think your most-likely culprits are, in order: 4. Bad water pump, 5. Coolant level–are you sure you put enough in? 6. Bad temp sending unit, which should be near the thermostat housing.
It’s also possible that you got a bum thermostat. Luckily, this is easy to check. Remove the thermostat and run the car without it.
It is a gas engine …system has been completely flushed…nothing but VW coolant has been used, and water of course, during the flush…only two items left are Fan and Pump…really hoping its not the pump…read somewhere that if I take the small hose off of the top of the reservoir, I can tell if its the pump; can anyone confirm this?
“read somewhere that if I take the small hose off of the top of the reservoir, I can tell if its the pump; can anyone confirm this?” — Not really, only if it’s completely dead. It may be moving water but not nearly enough water, and unless you have some way of measuring the flow you won’t be able to know.
…so I finally found a store that has the radiator fan; I should be receiving it on Thursday. My question now is the radiator I bought is thinner than the one that came with the car…is there any benefit to a thinner radiator or should I put back the original one?
Radiators have cores in them. This is basically the number of holes from the front to back. 1 core would be one row of holes. 2 core would be 2 rows of holes and so on. I would never go less than what the car came with.
Ok, so I changed the fan and it is still overheating… I guess the next step would be the water pump. What I noticed was a lot of bubbles in the reservoir, and the level fluctuating up and down…is that normal or a tell tale sign of some thing bad?
This is simple to diagnose and failed water pumps are common on these (I assume it’s the 2.0 engine?). Take the small hose off of the round coolant tank, start the engine and rev it to about 2000 rpm. You should have a fairly strong stream of coolant coming out of that hose. Alternately, remove the thermostat (it’s at the engine side of the lower hose, right?), and look in the housing. At just the right angle you will be able to see the impeller (fins) of the water pump. They will be plastic. And chances are they will be no longer firmly attached to the shaft of the pump. If you can move the impeller with a screwdriver you have a failed water pump.
it is a 1.8T but you are spot on with the location of the T’STAT. I did take off the small hose on the reservoir and the stream was not steady. I am in the process of changing the water pump at this point. Thanks
ok, so after much effort and finally some help from my uncle I was able to the engine mount off and get to the water pump. turns out that the impeller came off and I guess was just sitting in there. I am yet to put everything back together.