Overheating trouble

joshuare · Post by **joshuare** » Wed May 02, 2007 8:07 am

also, does anyone have any thoughts about the gauge thing? as I said I have a gauge cluster from a gas rabbit (mines diesel). could it be reading accurately? too high? too low? any thoughts?

Buzz · Post by **Buzz** » Wed May 02, 2007 8:32 am

joshuare wrote:woah woah woah, bad head gasket? I don't see the connection. We're talking about the hose that runs directly to the top of the expansion tank right? The coolant doesn't trickle out of that hose or anything, but it also doesn't flow in a steady stream. It comes out at a strong, fast pulse. Bad head gasket?

The pulsing that you are seeing is caused by the piston compression. The gasket failed between the cylinder and the water channels allowing the compressed air into the coolant - hence the pulsing of the coolant in the expansion tank line. Does the pulse rate change with the RPMs?

tylernt · Post by **tylernt** » Wed May 02, 2007 8:42 am

Gas and diesel temp gauge should be the same.

The head gasket *might* be blown. The test I use is to start a stone cold engine and let it run for just 10 seconds. Then shut it down and crack the coolant reservoir cap, listening for pressure escaping. Pressure = bad gasket.

Don't freak out yet, the pulsing could just be from air trapped in the system or air getting in near the thermostat/water pump (yes, the suction side of the water pump can suck air into the system through a tiny leak). It is common to blow the gasket whenever you overheat, though. Overheating is the weak point on these engines.

joshuare · Post by **joshuare** » Wed May 02, 2007 5:14 pm

having checked the expansion tank again, it actually seems like the fluid is coming out more steadily than I thought. I checked it with the engine idling. I'll try the test tylernt suggested.

so you think the gas/diesel gauges are the same? as I understand it the diesel runs about 30 degrees F hotter than the gas rabbit. Should I expect the gauge to always be a little high? I live on top of a very big hill, and the gauge usually gets almost to the red by the top of the hill, but then will fall almost to the middle within 5 minutes of stopping and letting the engine idle.

tylernt · Post by **tylernt** » Wed May 02, 2007 5:40 pm

Gas and diesel Rabbits both use the same part # for the temp gauge sender, 171919521F, so there should be no difference in the gauges.

Most VW gauges read slightly to the hot side of middle.

I don't have my Bentleys right now but I'll try to remember to check tonight. They list the factory thermostat temperatures. However I think gas and diesel are both supposed to be 187*F or 80*C. If you are having overheating issues then a cooler thermostat, 160*F or 71*C is available (that's what I run). You should also get a cooler radiator fan switch to match the cooler thermostat, though.

CoolAirVw · Post by **CoolAirVw** » Wed May 02, 2007 7:51 pm

joshuare wrote: I have also found that I need a new water pump. The pulley moves around considerably on the pump. I tested it by removing the thermostat, then filling the cooling system with water, removing the top radiator hose from the radiator and checking the flow of the water coming out of the hose. It flowed very weakly and irregularly so I figure I need a new pump too.

You allready know the answer.

tylernt · Post by **tylernt** » Wed May 02, 2007 8:44 pm

Well I just confirmed from the Bentley that the diesel runs at 176*F or 80*C. My gas book only goes up to 1979, but it says 85*C or 185*F for the gas engine so it's the gasser that actually runs a bit hotter.

joshuare · Post by **joshuare** » Thu May 03, 2007 8:17 am

huh, i did not know that. i wonder if my thermostat runs too hot. anyway, last night i put in a new water pump and fan switch, flushed out the hoses I didn't replace, etc. the fan works again! the gauge gets to two lines below the first red line then drops back down one, comes back up, and so on forever and ever. i still want to take it on a good long drive but it seems like my overheating days may be over for now. i wonder, should i invest in a new thermostat? as i understand it the diesel runs better when its nice and hot - not too hot, but also not under hot.

tylernt · Post by **tylernt** » Thu May 03, 2007 9:39 am

Yes, the hotter it runs the better the efficiency is. With the cooler t-stat that I run, I only average 40MPG in 100% city driving.

Your gauge sounds little hotter than normal. I've blown head gaskets before hitting red on the gauge so I'm a little concerned. But, maybe your gauge is just off.

joshuare · Post by **joshuare** » Fri May 04, 2007 7:52 am

I just wish that there were a way to gauge more accurately whether it is getting too hot. With the gauge a line or two below red - where the fan comes on - i can still squeeze the top radiator hose and it is still quite flexible. There is definitely a lot of pressure, but it isn't too hot to touch for a few seconds and will give maybe a centimeter or so from both sides when I squeeze it. A good sign maybe?

joshuare · Post by **joshuare** » Fri May 04, 2007 7:53 am

maybe not a full centimter. maybe half a centimter.

tylernt · Post by **tylernt** » Fri May 04, 2007 9:34 am

Easiest way I know of to test fir sure is to put a candy thermometer in the little stream of coolant coming into the tank.

Asymtave · Post by **Asymtave** » Fri May 04, 2007 10:41 am

Awhile back I made up an adapter to allow me to use a auto parts store temperature gage on my truck. I bought some barb-barb steel fittings equivalent to the inside diameter of the heater hoses. Then I drilled a hole in the center of this fitting and brazed in half a pipe nipple to make a "T".

The pipe fittings that come with the water temp gage kit will allow you to adapt up to a 1/4" or 3/8" pipe thread I think.

The problem is where to place the sensor/T fitting? The problem is that there is no where that coolant is always flowing (I don't think.) I thought I was being smart by putting my "T" in line with the hose that runs from the front head fitting to the water pump. Then someone here pointed out that when the T-stat opens water stops flowing in this bypass hose. The hose to the heater core doesn't really work because VW uses a valve to control heater temperature. In other words, you don't have any coolant flowing in this hose if it's summer and your heater control is set to Cold (on an A1 anyway.)

So - I've got an aftermarket water temp gage that indicates temperature very well as long as the thermostat is closed. I'm open to suggestions on where to better place this thing.

tylernt · Post by **tylernt** » Fri May 04, 2007 10:54 am

In my opinion, the best place is the water neck on the front of the head where the upper radiator hose and the bypass hose connect. With the thermostat closed, water flows past this location down to the bypass hose. As the t-stat opens, it flows past this location to the radiator. Some factory water necks come with a threaded hole for a sensor here (the A/C equipped models have a high-temp cutout switch to disable the A/C clutch when the engine gets a little too hot). You may be able to screw a threaded adapter in there and use that.

If you want to tap into a hose, the bypass hose would probably work ok as long as you tapped into it as high as possible -- with the barb practically touching the water neck. Hot coolant flowing to the radiator will heat the standing coolant in the bypass hose to some degree -- it won't be perfect and you'll probably get a bit of delay in your gauge reading vs reality, but I think it would work ok. That's basically the way the stock sender works, it's in the heater hose water neck which gets no flow when the heater is off, but it's close enough to the head to get a decent (if not perfect) reading.

Asymtave · Post by **Asymtave** » Fri May 04, 2007 12:41 pm

Thanks. Good call on the front water outlet. You're right - coolant has to flow through there no matter what.

To keep it simple maybe I'll just get a new bypass hose and put my fitting as high as possible and call it good enough. Unless I want to try my hand at welding an aluminun half pipe nipple to the head outlet. Better get a spare before I try that....

Thanks again.