More car troubles... need advice

[mr.72]

I don't think that's a pressurized reservoir. I think it's more likely that it has a radiator cap with a valve that runs to the overflow tank.

If it is overheating when idling and not overheating when it's driving down the road then it distinctly points to a problem with the fan. I know you say the fans are working "correctly" but you should really verify that in absolute terms since this is precisely the symptom of a fan that's not working.

The fan should have a thermostat that turns it on and off, one for the A/C fan and one for the radiator fan. They should both blow in the same direction, and that is they should draw air through the rad into the engine bay from outside. You may also want to check and be sure the radiator fins are not bent or smashed near the fan, or that there is no junk in there so that the only radiator fins that are not obstructed are the ones outside of the fan area. However I think since you said you replaced the radiator that the odds are relatively high that the fan(s) are not hooked up or working correctly. Maybe the thermoswitch for the fan is in the wrong place, maybe the A/C and rad fan thermoswitches are mixed up, or some other problem. Get a shop manual and go through the troubleshooting in it.

I hate dealing with cooling system problems. Two H2O VWs and a 70s BMW did me in. My Miata has a 5-core aluminum racing radiator. Now that's cooling capacity!

EDIT: oops I missed page 2 of this thread, looks like you got it fixed. But I would caution you against buying a VW if you don't like dealing with cooling system issues. I had two VWs that both were plagued with problems. Basically the problem is that they use a couple of plastic fittings in places where a Real Car would have metal cast parts. These can crack or expand and deform under heat and cause the pressure to drop and coolant to blow out as steam, which drops the boiling temp and the car will overheat every time. By the time you turn it off and get the coolant refilled it has cooled enough that the leak goes away and you can't find it. I did this over and over with these two VWs. Once you know the fix it is easy and you just have to keep an eye on it. But I'm not convinced that in 30 years VW has really figured out how to do water-cooled yet.

[pdubyoo]

Running a car like yours without a thermostat is a recipe for overheating. Even when a thermostat it open, it still restricts coolant flow through the system. Without the thermostat, even while open, the coolant will go through the radiator to quickly for the heat-exhange process to work...thereby allowing superheated coolant to travel back into the engine and be completely ineffective.

Replacing the thermostat is a simple operation, and should be done at least every 100K miles. They are relatively cheap too. The boiling and pinging noises you heard are likely due to a stuck thermostat. Also, if you haven't done so, go ahead and change your radiator hoses too. They can weaken and kink, causing an excessive restriction of coolant flow.

The normal temperatures at highway speeds vs. overheating on surface streets makes me believe the thermostat isn't the problem. If a thermostat stick closed, you're going to overheat, no matter what. At highway speeds, you have forced air moving across your radiator, completing the heat-exhanger process. During stop and go driving, without the forced air flow across the radiator, your overheating, which indicates to me that there is an air flow problem. This could be diminished with lower ambient temps, but doesn't completely go away.

If you have electric fans, there is a thermo-fan switch that normally screws into the bottom of the radiator (usually with two wires going to it). This fan switch looks like a fat brass pipe plug with a couple of wires coming off it. The function of this switch is to tell the electric fans when to turn on and off, based on coolant temps in the bottom of the radiator. These switches do go bad...it's not uncommon. If the switch is not telling the fans to turn on, that would explain why you're overheating in stop-n-go driving. It is also possible that the electric fan motor has gone bad, and isn't spinning fast enough, or at all.

It doesn't sound like you have a blown head gasket or cracked block to me. However, it is possible to have a cracked head, which could allow exhaust gasses to superheat the coolant, but that doesn't fit your symptoms.

I recomment concentrating on the thermo-fan switch or the fan motor(s). But I would go ahead and replace the thermostat anyway. One last thing, many newer engines are equipped with small bypass hoses throughout the cooling system. I have seen many bypass hoses with an air bubble that couldn't escape, causing overheating problems. Make sure that none of the bypass hoses, if equipped, has an air lock.

I also second the previous post that recommended a Haynes manual. These are based on real-world experiences from regular joes. Good Luck!

[lonewolf]

+1 on the fan/fan switch issue. Been there. Done that. Inexpensive and easy fix. Hopefully it'll turn out to be that easy.

[Taltyman]

Some fans have clutches and the clutch can slip. That allows the fan to appear to be functioning but its not really spinning fast enough to do any real good. When you are driving then the wind and the speed of the water pump helps out.

[TLE2]

Look into the fan sensor. It may be that the fan is turning off at slow, idle speeds.

[G.A. Heath]

Hey Russell, seeing as you have an electric fan, next time it starts to overheat turn on your AC. If your car starts to cool off then you do have a fan issue. A properly installed electric fan will engage when the AC is turned on regardless of the engine temperature.

[lonewolf]

It is in fact supposed to relieve pressure. You have a problem, my friend. You didn't put the thermostate in upside down, did you? Just checking.....Have you checked your fan(s) again? How about your belt(s) and or water pump? Not likely to be a coolant leak if the reservoir filled up and the cap was blowing steam, in my opinion.

Keep it simple. Take the belt off (usually simple) and rotate the water pump pulley. Does it spin like it should, or is there a binding anywhere? The pulley shaft should not wobble, either.

[lonewolf]

You may not be getting oil in you radiator from the oil jacket to the water jacket, but you may be getting coolant to your oil side. Check your oil and make sure it isn't emulsified (milky brown/frothy). Make sure the level is not overful, because that would be the oil level increasing with the coolant.

Blew a head gasket in a Chevy once and filled up the oil pan before I could get off the freeway. Catastrophic failure. Locked the motor up on that one.....

Have you noticed any white smoke from your exhaust, not the cold weather/early morning type, but the billowing stinky heavy stuff......

Just trying to help.....

[flb_78]

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You could try this. You have to completely flush the system of all antifreeze first. A fella on the Venture forum used it and sealed a leaky head gasket on his Dodge Ram with umpteen million miles on it.

[NAVY CHIEF]

Russell, if you can get to an AutoZone or Advance Auto, they have a loaner tool program. You can go "borrow" a cooling system compression tester (which I just did for my son's truck) to find out if your radiator or other parts have a leak. If you need "how-to" come back, we can fill you in. It could save not only your engine, but unnecessary parts.

"Carry" on!

Hooyah!