weird cooling system problem

[chrissev]

Maybe someone out there can diagnose this:  I'm driving on the highway and the cooling light starts flashing (gauge all the way to the top, pushing the white line).  So I stop, pop the hood and feel the radiator.  Cold.  Feel the bottom hose going to the pump.  Cold.  Feel the top hose, hot but I can still touch it.  Cooling reservoir also hot but not boiling over.  Take the top off the reservoir (slowly) and no coolant comes out, no steam, nothing.  So I figure I'll let it idle for a bit and watch what happens.  So I do that, and then I touch the radiator again after about 5 minutes.  Hot and getting hotter.  Touch bottom hose, warm.  Go inside car and look at cooling gauge, it has come down to about 3/4 of the way up.  Little bit after this, fan comes on and gauge goes all the way down to the middle.  So now I am stumped.  If the engine was that hot, why was the radiator cold?  And if the thermostat is not working, why did it open up when I was idling, but not under load at high rpm on the highway?  All I can think is that the thermostat is opening too late, but it is brand new and I just put it in this summer.  Either that or the gauge itself is giving an incorrect reading.  Anyone have any ideas?

[srivett]

My car has also done this once.  After about an hour of zipping around back roads I was on my way home and climbing a mediocre hill...  Suddenly the gauge goes from 1/4 all the way past HOTTER THAN PLASMA much to my dismay.  So I pull over, turn the defrost on (kicks in the rad fan on cars with AC) and start looking under the hood just as you did.  The system felt pressurized and the upper hose was hot while the lower hose was cold.  No signs of concern could be found so I drove home and never had another problem.  

After some reading and testing I believe I concluded that a HOT reading indicates a ground to the sensor wire.  I also found that my sensors wiring had been interchanged.  Once I swapped the wires between the glow plug sensor and the temperature sensor I started to get 1/2 as the usual temperature instead of 1/4.

But, the cold lower rad hose still had me confused.  I then switched the thermostat for an OEM one worth 35 CDN!!!! and no change.  My conclusion with regards to the lower rad temperature was that if the outdoor temperature is below 10C your thermostat won't open.  In fact, I've driven 600 km non-stop and found that my thermostat hadn't opened.  The upper half of your rad will be hot but the coolant doesn't appear to switch back for the lower half of the rad.

Steve

[chrissev]

2) Water Pump. This one is a bit more difficult to check. Possibly, the impeller on the pump has come lose from the shaft and is not moving enough water when the engine is at speed and under load.

Yeah, I thought that.  But it seems to be moving absolutely NO coolant when the engine is at speed and under load, but it moves coolant fine when the engine is idling.  

I was thinking of this problem and it seems to only happen when it is cold outside (on a hot day in August, going down the highway, the engine temp is normal and I have no trouble, but on a cold day in December [like today] my car overheats).  So I just thought of this plan:  I will tie wrap an oven glove to the thermostat housing and bottom hose to insulate it, and try driving the car hard on the highway at high rpms and see what happens.  My theory is that the cold air blowing on the housing is keeping the thermostat from opening.

Also, does anyone know what wire is the one that goes to the temp sensor gauge?  Is it a yellow and blue one, like on the old rabbit diesels?

[fspGTD]

I had a problem before with a thermostat I installed by not removing the power steering pump.  As the power steering pump was in the way, I had a hard time getting to the thermostat bolts.  It was a mistake to try and fasten down the thermostat cover without removing the power steering pump.  What I ended up doing was not tightening the cover squarely, and the thermostat sheetmetal structure sticking into the hole got cocked sideways somewhat and this caused the thermostat to get bent a little, and the moving part of the thermostat to have a bind when it moved up and down.  It still worked somewhat, however it didn't respond or work as completely as it should... this manifested itself in a bunch of overheating symptoms I had a heck of a time diagnosing, including a blown head gasket.

Also, don't drill a hole in your thermostat, or else your engine won't warm up at all or at least not very quickly in cold weather!

I found that on my Rabbit, the glow plug sending unit and the coolant temp sending unit have identical part numbers and electrical resistances.  I hope you can track your problem down... good luck.

[srivett]

The heatercore has a shutoff valve in it?  :shock:  I just assumed it was always on and you controlled the temperature with a cold air vent.  I disconnected my heater core connection on the end of that metal pipe and connected it to the extra nipple that's supposed to be for the oil cooler.  The reason I did this is that I connected an engine heater inline with the heater core but needed a much lower connecting point...it would be bad if there's a valve in it somewhere.

I found that putting a touch of silicone on the thermostat housing made it possible to reinstall the o-ring.  Without the silicone I would have been burried in snow by the time I had everything lined up properly.

Steve

[fspGTD]

On A1s, the heat lever controls the amount of coolant traveling through the heater core.

Starting with A2s, VW changed the design so that the heat lever controls a flap that varies the portion of fresh air flowing through the heater core.  They got rid of the heater core coolant flow valve also with that change (so that coolant flow through the heater core is always "wide open".)

[chrissev]

well, just found out something interesting about diesel jettas....you can't remove the water pump, without first removing the fuel injection pump.  Wonderful.  And the Bentley manual says "replacing a water pump is easy and requires only simple hand tools"  Yeah right, thanks Bentley.  It requires removing the timing belt, resetting timing, retiming pump, basically taking the whole front end of the engine apart.  I guess you don't have to take the injectors out to do it  :wink:

On another note, had a nice little engine fire today when the ground to the transmission from the battery melted down on me.  I guess it wouldn't have caught fire like it did, if the people who oil sprayed my car for winter hadn't had oil sprayed the transmission as well.  Luckily I saw it and put it out in time before the whole car went up.

[srivett]

Are you sure?  You have the choice of ordering half of the waterpump or all of the waterpump.  There's a raft of little bolts pointing out towards the pulley to remove if you order the half of the pump.  If you want to remove the entire thing you have to remove the bigger nuts facing the front of the car.  I've never done it myself but I really don't want to hear what you say is true.  

My tip for the - battery cable is to leave the old one on (place out of the way) and put another one on to another engine bolt.  Change the positive one too, they are cheap.  The Canadian Tire ones with the blue cables need to be reamed out to fit flushly onto the + terminal.  Your small connectors will have to be filed out to fit onto the bolts as well.

Cheers, Steve

[chrissev]

Are you sure?  You have the choice of ordering half of the waterpump or all of the waterpump.  There's a raft of little bolts pointing out towards the pulley to remove if you order the half of the pump.  If you want to remove the entire thing you have to remove the bigger nuts facing the front of the car.  I've never done it myself but I really don't want to hear what you say is true.  

Tried that.  I only had half the pump anyway (didn't buy the whole pump, too expensive) so I decided that if I couldn't get the old pump out, I would just take the pulleys off the side of the engine, remove the plastic timing belt cover, and undo all the little bolts and take the one side of the pump off.  So I did that, and guess what?  Intermediate shaft pulley blocks 3 of the bolts.  You can get at one through the holes in the pulley, but the other two, no luck.  One you almost can, other is completely covered.  I tried every way and you can't get at it.  So I had to put all the pulleys back on again and admit defeat.  The only two ways I can see that you can get the water pump out would be #1 take out the injection pump, or #2 take off the injection pump pulley and remove the backing plate so you can get at the bolts from behind, but with that way you would probably only be able to access one of them.  Either way you have to take the timing belt off and probably reset the pump timing as well.  It looks to be a huge job.  Hopefully my water pump is OK because I'm not looking forward to doing it.   This car is a turbo diesel so if you have an NA car it might be different... turbo pump seems bigger.

My tip for the - battery cable is to leave the old one on (place out of the way) and put another one on to another engine bolt.  Change the positive one too, they are cheap.  The Canadian Tire ones with the blue cables need to be reamed out to fit flushly onto the + terminal.  Your small connectors will have to be filed out to fit onto the bolts as well.

Cheers, Steve

Thanks.  I found a place on the tranny to mount a new ground bolt.  The old one broke off when I tried to remove it (after the connection melted down - too many amps for too rusty a connection).  It works great, starts quicker than it ever did before.

[chrissev]

In all likelyhood, you'll end up having one or more of the little 6mm bolts that hold the pump assembly to the housing break off and will have to drill it (them) out, so having the housing off the engine will make that process less painful and more possible.[/quote]

On my 88 Jetta TD, the top two bolts that hold the water pump and alternator bracket on are behind and underneath the injection pump.  I tried every tool I have and I cannot reach them.  They appear to be 13mm bolts, and they are visible, but like I said, I can't get a socket on them.  If you have an earlier car, like say a rabbit for example, you will be able to remove the water pump easily.  I know because I replaced the pump on my 79 rabbit and it took about 1/2 an hour to get it out.  But the Jetta is different.  I can't reach those bolts with any tool that I have.  Maybe you know another way to do it?  If so, please share!

[ejust]

if i may throw my two cents worth in here. i have an 86 TD Jetta. There is absolutely no way to remove the waterpmp without romoving the injection pump. The two upper bolts that hold the alt bracket on are inaccessable. I went thru this fall of last year and found out the hard way just after i installed a new timing belt and se tthe timing for the first time ever on a diesel. What a pain! I will say one thing, the gassers are easier in that respect.