Mongo

Thermostat was changed back in 2008. I suppose it could die in 9 years. The speed of slippage is something I was considering also. However if the thermostat was bad, why is it running at the first white mark while on the freeway? My wife had a Jetta that had an impeller slip at high speeds, causing an overheating issue. At idle, it looked like there was nothing wrong with the water pump.

Is it even possible to have low speed slippage, then at freeway speeds, show normal functioning?

Also, IF there is still air in the system what should I do to bleed it out? On a 944, there was bleed screw on the top water jacket. These cars don't have it.

Mongo

I was also thinking about impeller slippage.. is it possible for it to slip at low speed and not high speed?

This pump is still like new too!

dr bob

Andy--

I was in denial about thermostat issues but had an epiphany when the thermostat was changed after a lot of others stuff was done, suddenly a lot of odd temperature symptoms were suddenly gone. Thermostats are cheap and easy to change, so when I read about your odd symptoms it pops up on my list, For $20 you eliminate the possibility and move on. My symptoms started about ten years into the life of a thermostat I'd installed in the first couple years of ownership. I wanted to baseline everything.

The thermostat was closing and opening at the correct temps, just not opening enough to support higher-load higher RPM operation on hot (95º+) days. It wasn't closing all the way either but that part didn't show up in any driving symptoms.

The impeller slip at low speeds and no slip at high speeds is extremely unlikely.

If the car drives at normal temps with RPM's up, you've purged the air from the system already. You obviously had the heater valve open so air in that high section has moved on to the reservoir by now.

--- You might want to confirm the guage readings with an IR thermometer looking at the water bridge metal temps.

Mongo

Hey Dr. Bob, you have a good point. I am going to order a 75C thermostat right now. I also have the same temp one in there as well. It suddenly dawned on me that there is that darned seal behind the thermostat in the housing that fails too! At idle, and with a partially open thermostat, that can also cause some funky readings. I also know the gauge may not be the most accurate either. Clearly taking the pyrometer the first time around and getting the readings on the hoses in post #1 proves it.

I think you are right. I'm going to give it a go and bump this thread after I drop it in. Right now, it's family time as my toddler just woke up from her nap.

safulop

I had a thing like this happen in my old 944, it turned out to be a badly rebuilt water pump, where the impeller was binding at low rpm letting the timing belt whizz across it without turning, then high rpm it would kind of come unstuck. This went on for a couple of weeks until one day it just froze completely.

Mongo

The water pump was a brand new Laso when installed in 2013. Not sure how quality control is at Laso, and I hope that is not the case with the impeller on this one.

Going to try that new thermostat and inner seal to see if that fixes it before ripping the water pump out and timing belt.

safulop

Yeah the rebuilt pump that did this for me was about 9 years old at the time so, pretty unlikely in your case. If it is actually doing this, though, you may hear a high-pitched whining from the binding semi-stuck impeller on the shaft.

Mongo

Crap. I am hearing something like that on acceleration. I thought it was the alternator actually as it sounds similar to a supercharger whine. I already know this alternator needs to be replaced...AGAIN.

safulop

I feel you brother... old cars are just headaches waiting for someone to have 'em.

dr bob

Andy- take a look at the belt through one of the vent ports at the top of a belt cover. It the pump has been dragging, the belt has been sliding on the stick pulley. It will be --really-- polished from that. Like glossy polished. A stuck water pump offers almost instant overheating, if that helps your diagnostic process.

Start with the easy/inexpensive/most probable causes first. Pump impellerrs don't suddenly start binding in the scroll and slipping on the shaft. Thermostats do stick. Easy low-dollar options first: thermostat and seals top that list.

Mongo

The good news is the belt doesn't look like buffed flooring. It looks like a timing belt with minimal wear.

FredR

Andy,

By all means change out the thermostat with a new unit but not the 75C unit. Simply put it just does not fit in with the fan temperature programming and Porsche knew what they were doing when they specified 83C.

The rear seal is critical to opertion. No idea why they suffer attrition but they do.

I struggle to understand how a "slipping impeller" can occur in a manner to explain your symptoms and that before one considers whether such can happen- I have had two shaft to impeller failures and there was no mistaking the symptoms and the impeller dropped out of the casing when the pump was removed.

More to do before you go down that slippery slope!

Rgds

Fred

Mongo

Small update. I didn't have much time before work tbis morning but got the car back up to operating temp to take readings with the pyrometer. It is literally the same info below as I posted in the thread opener.

Top radiator hose was again 180-183. Bottom hose this time 162-167. The temp gauge still showing it wants to overheat (top white mark) and no heater unless I stand on the gas pedal at 3000, which drops the needle down to in between the two white lines on the temperature gauge.

I really doubt this is a water pump issue.

soontobered84

It may not be a water pump issue, but it does sound like a water flow issue.

I just had the first failed thermostat on the Stepson in all my years of working on cars recently. I always heard about thermostat failure and have replaced plenty but the first time I ever actually tested a thermostat and it didn't open.

Andy, when was the last time you flushed your radiator? Might be a real good time to get it cleaned out if you haven't lately.

Mongo

Flushed back in 2013 when I did my water pump and timing belt. Problem may have started back in December when I first noticed the temp gauge acting weird.