AAZ overheat?

[92EcoDiesel Jetta]

The cast metal impeller moves more water than the stamped steel impeller. My temp gauge went up a little after replacing a cast impeller pump (w noisy bearing) with a stamped steel one.

[745 turbogreasel]

I think your  impeller might not be pressed all the way on.

[8v-of-fury!]

The aaz's never had a water pump that ran off of the serpentine belt. It was always on v-belt with the power steering as well.  1Z/AHU tdi's were the same too.

I do not think it is a backwards spinning problem because I have the same P/N water pump being spun by the back side of the serpentine belt on my AHU swap with no P/S.. And it moves coolant as it should, so that rules out that theory.

[Gizmoman]

Well, after all that, it did turn out to be the thermostat. The new one I put in is a 180 and the one that was in there was a 190 or possibly even higher. No numbers were stamped on it but when I tested it, it opened around 190. The new one has a larger diameter "gate" as well but I'm not sure if that helps or not. The temp probe is sensing coolant from the head and even when I push it, it's not going over 195. The stock gauge is riding dead center when cruising and moves slightly past the LED after a long climb - I'm a happy man.

Thanks for the feedback on the impeller. I left the cast one in place as it just looked more efficient - glad to hear that it is.

I also ran the combustion gas test and the fluid stayed blue. I did the test with the engine at 170F and pumped the vacuum bulb probably 50 times - stayed blue.

This is a real load off my mind. Now all I need to do is remove the valve cover and smear about a tube of silicone between everything. I've messed with it three times, putting blobs at the cam corners and all - no luck. It's the only leak I have and it's making a real mess of everything.

[8v-of-fury!]

Haha, careful.. some people swear RTV is the devil. Put a small bead, and let it "tack" before mating the assembly. This greatly reduces the amount of squeeze out the blocks oil pumps hhaa.

[Gizmoman]

Haha, careful.. some people swear RTV is the devil. Put a small bead, and let it "tack" before mating the assembly. This greatly reduces the amount of squeeze out the blocks oil pumps hhaa.

I won't get too carried away. Just seems like of all the things on this that could leak, the valve cover should not be one of them. I've tried dabs in the corners, thin coats, checked the stamped metal cover for flatness, etc.

Time to get serious. I will use the grey stuff which claims to be impervious to oil and feels much tougher than others when it sets.

[Mark(The Miser)UK]

I thought VW engines tend to fall into two categories those that operate just over atmospheric boiling point of water and those that don't quite.
17-19psi running pressure + coolant additive takes boiling point significantly over boiling point. So, what's the problem?

As I've said before, try retarding pump a little. Don't 'Giles' pumps offer faster advance rates, and greater maximum advance, so starting slightly retarded from 'book' is not unreasonable IMO.

Why not just try it, measure the results and then go back if no improvement? The slight increase in heat out of the exhaust will be coupled with a bigger decrease in heatloss to coolant, and more pressure doing work ATDC, IMO...

[8v-of-fury!]

I thought VW engines tend to fall into two categories those that operate just over atmospheric boiling point of water and those that don't quite.
17-19psi running pressure + coolant additive takes boiling point significantly over boiling point. So, what's the problem?

Truth, when I was hitting 230F I was not at all worried. New hoses, new rad, new bottle and cap.. Had the coolant additive as well.. Nothing bad went wrong, didn't even burp any coolant.

[745 turbogreasel]

Hooray for cheap  $easy solution, i thought you'd find that.

If you have the shouldered studs  for the valve cover, be certain they are all sunk to the flange, or it will for sure leak, and be a pain to remove.

Has there been any change in EGT?

[Gizmoman]

Hooray for cheap  $easy solution, i thought you'd find that.
If you have the shouldered studs  for the valve cover, be certain they are all sunk to the flange, or it will for sure leak, and be a pain to remove.
Has there been any change in EGT?

I can still hit 1300 pretty quick getting on the freeway - typically a short climb to boot. My intake charge air temp (CAT?) still seems warmer than it should be but I'll live with it for now. The goal is dependability and only time will tell.

It's great to hear that the engine can get so hot without damage. Maybe I am a bit wary, but I can imagine the Mojave, a long climb, and in August no less. To me, if 180 is on the thermostat, and the system is up to snuff, 180 is where it should stay.

Really appreciate all the feedback and good info. Thanks again.

[wolf_walker]

Just to beat a semi-dead horse, brand of the old and new t-stats?

[745 turbogreasel]

GM doesn't even turn the fan on till 230(the thermostat is  wide open long before that) on Vettes and Camaros, part of how they get such good highway MPG(and bake the hell out of the harness wrinkle wrap).


Brand? I think thermostats are just weak, and I've seen a dud from every brand.

[theman53]

cast has been the better choice for me

[Mark(The Miser)UK]

Remember that the thermostat opening  temperature isn't the system operating temp, but the initial 'rapidly' achieved engine temp before the additional circulation of water occurs.
Then there's the hysteresis, allowing engine temp to drop, yet the gate remains [partly] open, then further, [higher rises] as the engine produces more heat. Otherwise interior heater would be cold to start  followed by more noticeable pulses of hotter, then cooler air. Well that's my take on it  

[Gizmoman]

Just to beat a semi-dead horse, brand of the old and new t-stats?

Yeah, just beat it!
Old one - don't know, no stamp or nuthin (not a good sign). The one that fixed it - Duralast from the parts house on the corner - 16 bucks. They had a better brand listed for twice that but not in stock.  It looks fine craftsmanship-wise and it passed the test on the stove.   Ironically, the one I ordered showed up today as well - after I got the local one in and the van running.

As far as high temps go, the stock gauge has always been the weather "vane" for me and it seems 180-190 is where it should be to keep the needle pointing straight up. More to the point, a stable temp is the most important if it's 180 or 225, it should be stable or something's not right.