[rustech]

My car, rather than riding near the 8-9o'clock mark on the temp gauge, is instead near the 10o'clock mark. I've bled the system over and over but only got air out the first 2(two) times. I've had the radiator out before, and never had a problem bleeding it, and so don't suspect any air pockets in the system. All variables are the same (as pre belts, variocam, seals, rollers, tensioner, hoses) with the exception of the impeller design of the waterpump and the thermostat. The thermostat rather than an aftermarket low temp unit, is a Porsche regular temp unit. I have a low temp fan switch installed. The impeller differences are in the pics below.



So this is the impeller on the new water pump:





This is a pic of the impeller in the old waterpump:





My old waterpump was also a rebuilt from who knows where. Zims Autotechnik (whom I purchased the new unit from) says that they use the same (rebuilt) impellers as Porsche. They checked a unit in the back, and it's the same as the new one I have installed and is supposedly the same unit. Sunset (Jeff and Phil) seem to recall the aluminum round solid version to be "newer" as that is what they recall most recently handling. Does anyone recognize one impeller to be a newer/better design than the other? Who has the aluminum disc (round solid) version in their car with no problems? Does anyone have advice for figuring out why my car is running hotter?

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[Cloud9...68]

Gotta ask the obvious question - did you replace the thermostat?

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[Greimann]

The shrouded impeller is a more efficient design. I think I remember that Flossdoc's pump was that way. That should not be contributing to the problem.

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[orphanowner]

First thing you need to do is read the temp off the old and new T stats if you can. That alone may answer your question. A lower temp fan switch with a 83C T stat is gonna have the fans on all the time, see gauge temp info below.



I actually have done the "boil test" on three different T stats and have validated that the centigrade temps are accurate. Some data points: OEM fitment is 83C/181F, aftermarket can be 80C/176 , and 71C/165F. There are big differences in gauge reading from each T stat. I like to run the 80C, as the 71C is too cold for a street driven car and will allow the formation of acids in the oil unless your trips are at least 45min or longer. The 83C allowed no margin for temp fluctuations and allowed the car to run too hot in my opinion.



Coolant temp gauge readings:

Bottom of gauge ( start of bottom mark) 104F 40c

End of bottom mark 140F 60c

First slash mark 176F 80c

Second slash mark 212F 100c

Start of top block 239F 115c







As for w/pump impellers, the solid aluminum part is the one I see most. I think that OEM can be aluminum, plastic, or stamped steel, depending on the vendor.



Here is a link to another P car forum where I regurgitated some info I've learned over the years on hot running 944 series cars.



http://65.61.16.109/forum/topic.asp?TOPIC_ID=11400









Good Luck.

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[rustech]

Orphanowner, I find what you say to be very interesting. I do have a new stock (from porsche) thermostat which is 83'c. If my needle only fluctuates in the top half between the white bars and the fans run all the time, do you find this to be my likely problem?



Dave (Greimann), can you comment on this (I recall a previous discussion related to this).



Thanks.

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[orphanowner]

[quote name='rustech' date='Nov 8 2005, 06:39 PM']Orphanowner, I find what you say to be very interesting.  I do have a new stock (from porsche) thermostat which is 83'c.  If my needle only fluctuates in the top half between the white bars and the fans run all the time, do you find this to be my likely problem?



Dave (Greimann), can you comment on this (I recall a previous discussion related to this).



Thanks.

[right][post="12204"]<{POST_SNAPBACK}>[/post][/right][/quote]





I just added more info to my previous post. Yes, if you have a high temp T stat and a low temp fan switch, the fans will run all the time.



Oh one more thing, that old w/pump is not the orignal on your 968. It looks like a rebuilt with a 1988 casting date. I never liked the open stamped impeller for the same reason Dave mentioned.

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[Eric_K]

The ones I've dealt with have all looked like the top picture.



Eric

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[flash]

ok - i have an 83 degree thermostat, and low temp fan switch - i've NEVER seen the upper white mark - it is almost always at or just below the 8 o'clock line (yes, i've verified accuracy of the guage) - during hard running (and i do mean HARD) it gets just above the 9 o'clock line



my fans rarely run at all, let alone all the time - they come on low speed just above the 8 line, and i have only heard high speed come on once



i agree that the issue is likely thermostat related, but i doubt it is because of using the stock temp - my first thought was that it might have been in backwards - my second is that it is faulty



p.s. - i have no idea which impeller i have - i have a 2.5 casting (don't get me started on how that happened) - still trying to find a way to see them side by side without taking mine off

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[orphanowner]

[quote name='flash' date='Nov 9 2005, 09:47 AM']

ok - i have an 83 degree thermostat, and low temp fan switch - i've NEVER seen the upper white mark - it is almost always at or just below the 8 o'clock line (yes, i've verified accuracy of the gauge) - during hard running (and i do mean HARD) it gets just above the 9 o'clock line



my fans rarely run at all, let alone all the time - they come on low speed just above the 8 line, and i have only heard high speed come on once





I have both fans switches in front of me at the moment, the standard is 95/102C, and the low temp is 85/92C. So if your car holds a coolant temp close to 83-84C, then yes, the fans won't run all the time and if the temp never goes over 92C, then yes the high speed fans won't cycle on. For most cars, it doesn't make sense to address a cooling issue with only a T stat change unless that part is defective. Like my post in that other forum that I referenced above, there are several reasons for a car to run hot.



There are big variables here...from radiator issues to gauge sensors, every car is different, but most of the cars I've seen with low temp fan switches and standard T stats run the fans all the time. Most cooling systems can't maintain temps within a 5 degree range.

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[Greimann]

[quote name='rustech' date='Nov 8 2005, 06:39 PM']... thermostat which is 83'c.  If my needle only fluctuates in the top half between the white bars and the fans run all the time, do you find this to be my likely problem?



Dave (Greimann), can you comment on this (I recall a previous discussion related to this).

[right][post="12204"]<{POST_SNAPBACK}>[/post][/right][/quote]



Like Mr. Orphan's table shows, the lower part of the temp gauge scale is where the thermostat opens. Once open, it is up to the cooling system's efficiency to keep the temps in check. So no, the thermostat rating is not the issue. It could be the standard things like - air bubble, fan not working, faulty thermostat, plugged radiator or impeller disconnected from shaft.

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[flash]

as far as i know, ron's and dave's cars both work about the same as mine too - no fans running all the time - that sounds like a problem all by itself



i didn't mean to imply that i was recommending a different temp thermostat - in fact, i do not recommend the lower thermostat - the radiator on this car is too small as it is (as shown by the fluctuations in temp during different running conditions) - the coolant would heat soak and not be able to continue to cool the engine



the best condition is one wherein the needle stays pretty stable (no more than a 15 degree change due to running condition)



a cooling system, when properly set up, runs about 100 degrees over ambient, or 5-15 degrees above thermostat setting, whichever is higher, regardless of running condition



to eric's problem, i would recommend a pressure bleed (about 18lbs), and then failing that solving the problem, yank the thermostat and inspect for fault



also, check the cap for pressure - i believe it should hold at least 13lbs

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[Greimann]

[quote name='flash' date='Nov 9 2005, 03:03 PM']as far as i know, ron's and dave's cars both work about the same as mine too - no fans running all the time -...[/quote]

Mine run frequently, not all the time. I am not really paying attention that much as you can't hear them when you are driving anyway.

.... in fact, i do not recommend the lower thermostat - the radiator on this car is too small as it is ...- the coolant would heat soak and not be able to continue to cool the engine

Ok, I'll bite. Why do you think a low temp thermostat will cause overheating?

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[flash]

not overheating, but running hotter - i suppose at the extremes, it could make for overheating - i now on the surface it doesn't make sense



here's the deal - the thermostat opens and closes to let cool water back into the block - this is a big set of cylinders, with a lot of heat being generated very quickly - the thermostat opens a lot already - add to that, if the capacity of the radiator is too small, as is the case with our cars, the water never gets a chance to stop and cool down, then doesn't have enough cool water to make up for it, it heat soaks, and then you have problems



we know you want your water to be about 190 or so for proper fuel combustion



we know that a proper cooling system runs about 100 degrees over ambient, or 5-15 degrees above the thermostat point



that means that, given a properly sized radiator, you should run about 185 degrees or so on the thermostat



the answer to our cooling issues is not in the lowering of the thermostat - it is in the increasing in efficiency of the radiator, either by the fans or increasing capacity of the radiator itself

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[rustech]

Thanks for the replies, I'm glad to hear I don't have to take my waterpump back off <img src="/forum/images/smilies/968/rolleyes.gif" class="smilie" alt="" />



If my thermostat opens at 83C...does it open fully and instantaneously?...does it open progressively from that point of 83C?...does it open progressively to that point? Is it possible an 83C thermostat doesn't give full flow until ~90C?

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[flash]

since i don't have x-ray eyes i can't see inside (that was a dealer option that did not come with my cape), but if the stove top tests are any indication, it opens fully at the temp setting and isn't exactly instantaneous, but not terribly slow either - a couple of seconds



i have no idea if it is even possible on this one, but if it is in backwards, it will read the temp on the wrong side, and do exactly what you are describing

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[rustech]

Not backwards. Really, it's not. I meant it the first time I said it.

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[flash]

lol - i know - i'm just having a hard time explaining it otherwise (sounds like a similar issue lately, whch also turned out ot be something that they "swore was right, but wasn't")



so, the probe points toward the block, and away from the radiator? i haven't actually had to look at this yet

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[Greimann]

[quote name='rustech' date='Nov 10 2005, 09:03 AM']If my thermostat opens at 83C...does it open fully and instantaneously?...does it open progressively from that point of 83C?...does it open progressively to that point?  Is it possible an 83C thermostat doesn't give full flow until ~90C?

[right][post="12260"]<{POST_SNAPBACK}>[/post][/right][/quote]



The thermostat temperature rating is the temperature that it is fully open. During cold start warm up it is closed, then close to the rated temperature it will gradually open. After that it is fully open all the time, unless you are traveling on the freeway in cold weather, then it may close a bit to keep the engine from over cooling.



Flash, I dont agree that a thermostat opens and closes a lot. Once the engine comes up to temperature, it is open all the time allowing the cooling system to do its thing. More flow means better heat transfer. The water never "stops" at any time unless you are in frigid temps and the thermostat has to close to prevent over cooling. so regardless of rating, it will never contribute to increased heating.

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[flash]

i used to think that too - and it really varies from car to car - i found this out the hard way when i was experiencing overheating issues on a pumped up motor that had been bored out a lot - i tried the lower thermostat thing and it got WORSE - stock was 195 - i tried 160 and even 140 - then i spoke with a few different guys who specialized in cooling systems, and they said that, while the amount of opening varies during running (it is a coil spring after all) it does in fact open and close - for example, a system with a fixed fan, that swings up and down in temp, during a steady state of operation, is a good example of when that is happening - pretty much any older car is like that - newer cars tend to do that less, because they also have thermostatically operated fans to assist in maintaining a more constant temp



i ended up with a bigger radiator, a thermostatically controlled electric fan, and a 185 degree thermostat - needle went to 190 and never budged, regardless of how hard i drove the car, or how hot or cold it was



a properly set up system, does in fact keep the thermostat fairly consistently open, and i agree with you there, but if the temp drops below the thermostat point, it will close - mine does it all the time - i still think i need a bigger radiator, but during normal driving, it's pretty much nailed now, and stays just above the thermostat point, but below the low speed fan point - on a cold day though, i don't even get to the thermostat point often - it will poke up sitting still, and then as soon as i get moving, go down and close again - i'm actually considering a higher temp thermostat when i go to a bigger radiator - we'll see



i'm determined to get back to that magic 190 number and stay there - more importantly, since i am there now under hard running, i want to get street running up from the 176 or so it is at now closer to that 190, but doing so at the expense of 212 during hard running is not acceptable

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[Greimann]

[quote name='flash' date='Nov 10 2005, 03:30 PM'].... but doing so at the expense of 212 during hard running is not acceptable

[right][post="12293"]<{POST_SNAPBACK}>[/post][/right][/quote]

Well as long as your story is about the MG then I suppose anything is possible, but in a normal car, a lower temp thermostat will not cause it to run hotter.



What is so taboo about 212? In a pressurized system water doesn't boil until about 265.

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