Dan87951

I'm just finishing up a timing belt, water pump, and rollers on my 87 S4. This will be the 3rd timing belt I have done on one of these cars. Everything went together as planned but when I was bleeding the cooling system with the radiator cap off and heat on full high the car would start to overheat (no hot air). I checked the thermostat and it works fine and opens when its suppose to but the interesting part is the radiator inlet hose is super hot while the outlet hose is just cool/warm. This leads me to believe I might have a water pump failure. I also noticed a rattling sound coming from the water pump area. Loose shaft? At this point it was getting to be 11PM and I closed shop for the night and will diagnose more tomorrow after work. Anyone have any ideas?

AO

Sounds like a bad pump.

dr bob

Dan,

Try rev'ing the engine a few times as you burp. Have the front end of the car high if you can too. I found that I gad an air pocket in the water bridge that kept the liquid from getting up to the point where it would fully flood the thermostat. Thermostat stayed closed and the car would get hot. Pulled the thermostat and tested it on the hotplate, worked fine. Bob scratches head, more hair falls out. Finally decided to try rev'ing the engine some, and the system burped a little, thermostat opened, everything fine from that point on. If you find the upper hose is hot and high-pressure hard, but the lower hose is cold and relatively soft, and that the fans aren't running, you likely have the same problem. Easy to diagnose as a water pump issue since there's no apparent circulation.

AO

You can try cracking open one of the temp sensors on the coolant bridge to allow any trapped air to escape.

Dan87951

Thanks for the advise. I will give that a try and report back. I did rev it a little last night but nothing seemed to help.

Big AL in VA

A bad water pump. The impeller inside is loose on the shaft. It is only a press fit with some magic sauce keeping it on. I had the same problem with a Chinese knock off pump. But, it can happen to any pump. The symptons you describe is exactly what I had with my pump. I took my failed pump to last years frenzy for a show and tell. Sorry, I know it is a PIA to take everything back off.

Dan87951

Your probably right even though I hate to believe that it’s the water pump. I got my water pump from a rennlist sponsor so I’ll be a little disappointed if its in fact the pump, but what can you do?

Where you also getting the rattle sound with yours? I'm guessing thats the impeller jiggling around on the shaft?

Bill Ball

Hot inlet and cold outlet is characteristic of no/very low flow through the radiator. No hot air from the heater nails that it is the water pump. I suppose the incidence of bad rebuilt pumps is very low, but on my personal car I inspect the water pump when I do the timing belt, and if the bearing is firm and quiet and all else about the pump is like new, I leave it alone.

SteveG

Someone was commenting that his mechanic was firm about changing a 6000 mile pump when a 5-year old belt is changed b/c a newly tensioned belt might overtension the pump pulley and it would fail. I commented that that mech must not be using a belt tension tool and should be avoided. This guy is probably overtightening at the outset to compensate for future stretching. The purpose of correctly tensioning a belt w/tool and then re-tensioning it at 1500 miles is to maintain the correct tension at all times.

marton

So send it back & they will replace it

Marton

ROG100

I am pretty sure Dan got his latest WP from me. I check them in a number of ways for obvious reasons.
This WP has a metal impeller and was solid on the shaft and span freely when twisted. There is no axial movement on the shaft either.
Of course if there is a problem with it and I supplied it I will replace it.
I will await the final diagnosis from Dan.

ROG100

Dan,
Is this not the second failure?
Maybe something else is going on?
Roger

Dan87951

No this is not the second failure. First failure was because I just threw a new belt on and did not replace the water pump at the time. After 10k miles the water pump siezed on me. My fault for trusting the PO's word regarding the age and miles of the pump.

This failure occurred without ever finishing the installation. I finished my t-belt yesterday, car started right up began my coolant procedure. Car would not blow hot air and I also heard a rattling sound coming from the water pump upon further inspection. Checked the inlet hose and it was hot and the lower outlet hose was cold, obviously something isnt circulating.

Dan87951

Obviously im trying to get feedback before I dig into a 8 hour job.

Dan87951

I went out and tried again same thing happening. Inlet hose is hot out let is cold. The rattling sound it gone though? I think I will dig into it to verify everything not worth bending valves over. Won't have time to start tonight have stuff to do for work.

Roger,

I'll keep you posted. Thanks. Just for the record if it is the water pump, "roger" is my new 4 letter word! I kid, I kid..