Overheating Mystery, please help.

[zepherous]

1998 golf cl 1.9 umwelt AAZengine.

Everything was fine until the coolant was changed, then after driving a few miles the car started overheating. The RAC advised to change the waterpump. So new waterpump and timing belt.
Refilled , the heater blew hot and the fans kicked in etc. Took the car for a short drive and it started overheating again. At this point I put it into a local garage who flushed the system and put in a new thermostat, it started overheating again on the way home.
Took it back to the garage and they changed a sensor and put in a new radiator, the car started overheating again on the way home.
The radiator does not get hot neither does the bottom radiator hose.
Please help , Thanks.

[Doug]

Sounds like you have an air lock that is not allowing the coolant to move around the system. Try running it with the cap off the reservoir until the lower rad hose feels warm. You may also have to check to see that the system is pressurising. If not, then suspect the reservoir cap. Replace it. They are cheap. It may also be necessary to replace the thermostat. The OEM thermostats are more reliable than the aftermarket ones that a lot of garages sell. Has the thermostat been installed correctly?

Is there a reason why you decided to change the coolant?

[Darth Garry]

If you squeeze the hoses while it's running it will help coax the air out of the system.

Garry

[burn_your_money]

You may have a bad headgasket. Remove the res cap and look for bubbles. You may also want to do a leak down test

[zepherous]

On the two occassions we have tried running it with the cap off for ages, the fans kick in and the heater is hot. The garage it was booked into changed the thermostat on the first trip........wondering if the new one could be faulty or not correctly installed? Hope the cap isn't a dealer only part, the nearest dealer is 15 miles away.
I will try the thermostat myself tomorrow.........how difficult is it to get to?
Took me 7 hours to do the waterpump and timing belt, even had to resort to getting my partner to loosen a couple of tight bolts which he won't let me live down.
I was giving the car a service oil fuel filters etc and decided it was a good idea to do the coolant as I had no idea when the previous owner had last had it done.
The needle on the temperature guage does not give a true representation of the temperature as when it starts to rise quickly it stops with a thud at 90, even when the engine is alot hotter.

Plans for tomorrow are: try running without the thermostat to see if the radiator and bottom hose gets hot if they do then try a new thermostat if not try a new cap and squeeze the hoses.

Plans if that does not work are ? No idea ....

[Doug]

I see in your last post that you did something to the timing belt. Have you confirmed that the timing is correct? If it is retarded it will cause overheating. Does the system pressurise with the cap on the reservoir? If it doesn't then replace the cap with a new one and try again. Sometimes when the coolant is replaced the head gasket if it was sealed with a temporary sealant like Barrs Leaks will again start to leak. You may be looking at a gasket job but a leak down test may help to detect that problem.

[jtanguay]

it has to be the vw thermostats... i too had the same problem as you, and switched to a pretty cold t-stat, and now have zero overheating issues.  

on hill climbing with boost at around 10-15 psi, the temp will gradually climb, but then the high speed kicks on for the fan to cool it down.

before when i had the vw t-stat, it would just keep climbing, and was pretty scary at times.  these diesels do run hot, but not that hot.

if you want, get a thermometer and put the t-stat in hot water on the stove.. gradually heat it up until around 100 deg C.  it should open fully by 90C.  if not, then that is your problem.  mine was barely halfway open @ 100C... i was not impressed as i payed $30 for it, and it was faulty!!!!!

[zepherous]

Thanks for the reply, the first time it overheated was before the timing belt was changed, at that stage it was just the cooland and oil etc that had been changed. When the RAC said it was the waterpump that caused it the belt was replaced as we disturbed it. The waterpump on this car is driven by the fan belt, the timing belt was removed so we could remove the pully wheel to get to the waterpump.
I went to get a thermostat from the motor factors today and discovered there were two listed for this car, they could not tell me which was was the correct one, but did tell me one was shorter than the other and that if the garage used the wrong one (they look very similar) then there would not be room for it to open. I'm hoping this is the case. It was pouring with rain here today so I never got a chance to do any work on the car, I use a friends drive and have no shelter. Hope the weather improves tomorrow epecially knowing the wrong thermostat may have been used (gives me hope that it will be that simple:-)
I don't know if the garage pressure tested it and after them fitting a new radiator without contacting me first we are no longer on speaking terms

[zepherous]

What thermostat are you using now ? A friend  told me they had used that a ford transit one as that opened at 80?

[jtanguay]

i put in the coldest t-stat that i could get... mainly since it is summer time.

160F maybe???

[Doug]

I believe that the correct one is a 87 C for Canada  but if you are in a hot climate then maybe you need a 70 C one. You need to find out if the timing for the camshaft and fuel pump is correct if it has been disturbed when changing the belts.

[jtanguay]

yep 87C when it's not defective  :roll:  still pretty pissed at the whole ordeal...

BUT... in the winter i ALWAYS had heat!  it warmed up so damn fast i loved it!!!  the faster i drove... the hotter it was... spooky?!

i wouldn't mind changing to cooler t-stat in summer & hotter in winter...

[jimfoo]

That's one thing I HATE doing on these engines, changing the t-stat, because you have to drain ALL the coolant out, but the block doesn't drain until the housing comes off, and it gets all over everything. Pretty soon, maybe this weekend, I'll get to see if mine still has overheating problems. I think it is just an AAZ thing. I don't know if they need a bigger h2o pump or are just damn hard to get the air out of. I modified my stat so it always flows a tiny bit of water, and so that it closes off the internal passage sooner. I also have Evans coolant, so no boiling, and 2 oil coolers and a new slightly larger Al rad and intercooler. Plus I don't think the oil cooler in front of the rad last time helped the water cool any so they are behind it now.  :roll:

[jtanguay]

a pretty easy way to bleed the air bubbles out of the system is to run the motor with the cap off.  that way air will easily bleed off (rev the engine up a bit to help circulate the water...

i wonder if there could be any mods to install some sort of valves to change the t-stat easier... close valves, remove t-stat, install new t-stat, open valves, bleed system

would be nice!

[Darth Garry]

I would recommend running the stock temp thermostat unless you live in the desert.  I put in a slightly colder one (82 degrees) I believe, and have difficulty getting decent heat, and the needle never goes over 1/3.

While excessive heat was bad, these engines were designed to operate more efficiently and with less wear and tear within a certain temperature range.  That range is achieved properly with an 87 degree thermostat.

As far as brand goes, I've always used Wahler(german made) thermostats and never had a failure.  It is good practice to always do the "boil water" test to verify that your thermostat is working before you put it in.  It takes a few minutes but then you're assured you have the a properly working 'stat.

Of course, based on your set of issues, it could be a totally different problem.  I've never had an issue with air lock, when filling the coolant I run the engine and squeeze the hoses to coax the air out.  It takes 10-15 minutes to get it under control.

Another question - in your adventures did you change any of your other hoses or connections?  Verify that all of your hoses are routed correctly (bypass hose, water pipe, oil cooler hoses).  I can't visualize it all in my head, but I could imagine that if a hose is hooked up backwards, it could cause some misery.

Just my .02, good luck with your issues.

Garry