1G 6bolt Overheats under load

[rdeis]

Hey, all. I'm not exactly a newbie, but I've been out of the scene for a while. I bought a broken 1Ga with an automatic transmission to fix up with my boys and it's got me stumped:

The car was parked for a long time, and the fuel system was predictable mess. We've got that all cleaned up now using injectors and ECU from a 94 Tsi and it's idling very nicely now and seems to drive OK, but it overheats under boost. It maintains temperature just fine at idle and cruising about the neighborhood on flat roads, but as soon as I start climbing a hill so the boost comes on, it start to overheat. Rest it at idle and it comes back down.

No obvious compression problems. New thermostat that appears to open and close properly. Replaced the radiator with a used one I had on hand and no change. No codes from the ECU or the TCU. No indication of anything amiss at all, actually, except that the temp gauge goes to the roof after we boost it for a mile or two.

I'd like to blame the gauge, but it reads cold and hot just as I'd expect it to- just right of center when the thermostat opens and the fans come on. Water pump is new, too, and I flushed the cooling system with clear water before putting the new pump on.

Has anyone else experienced something like this?

 

[ThunderChild]

Sounds like pushing coolant under boost or the trans is slipping the converter under load and heating up a ton.

Have you done a leakdown test? What about a trans flush to check the fluid for particulate? Fluid burnt?

Past that, i can inly think theres some air in there (less likely due to description of issue) or the WP is cavitating/broken shaft?

 

[Dsmkauai]

Make sure the coolant system is free of air. Can take abit to fully bleed out. And either do a coolant system pressure test or a leakdown test to rule out leaks.

 

[rdeis]

Have you done a leakdown test? What about a trans flush to check the fluid for particulate? Fluid burnt?

Replaced the tranny fluid recently and there was no sign of problems in the old fluid.

 

[rdeis]

Make sure the coolant system is free of air. Can take abit to fully bleed out. And either do a coolant system pressure test or a leakdown test to rule out leaks.

Past that, i can inly think theres some air in there (less likely due to description of issue) or the WP is cavitating/broken shaft?

Pretty sure I got the air out, but it does burp differently than my Tsi. On the good engine, when the thermostat opens the level drops and you top it off. On the problem car that happens, too, but shortly after that you get a giant belch that blows a cup or two of coolant out and then you have to put that plus a bunch more back in.

With the T-stat open the flow rate seems fine, maybe even a bit higher than I'd expect.

There's evidence the previous owner loaded it up with stop-leak, would this be consistent with some clogged coolant passages inside the motor? If so, is there anything I can do about it without tearing the whole thing down?

 

[ThunderChild]

Stop leak is the devil. Usually, i wouldnt figure itd stick inside the engine itself, but itll eff up radiators. I know you replaced the rad and wp already, so im thinking the stop-leak isnt a big issue. There are some rad flush oroducts out there that you can use to break up sediment and garbage in the cooling system, so you might try that.

It does sound like you have air in the system still, but usually that contributes to a constant temp issue.