[spectre996]

Alright, lately my temp gauge has been almost directly related to my speed. <35 mph and my gauge is approaching 10 o'clock. 35-50 mph and I'm near 9 o'clock, 55+mph and I'm a tick above or below 8 o'clock. It doesn't matter what the RPM's are, only which of those three "zones" I'm cruising in. Also, if I'm just idling the gauge is typically down near 8 o'clock again. The only thing I've done between it acting completely normal and my new "dancing" gauge is add a quart of oil b/c I was running low. Any ideas? Can having too much oil in the system cause the symptoms described? I think my water pump was replaced last time I had it in the shop (about 10 months ago) but I'll have to recheck my invoice.

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[968rz]

Not that this is your problem but that is the same symptoms my water pump showed when the impeller spun on the shaft.

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[flash]

are all of the belly pans in place?

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[spectre996]

Should be. I've never removed any, but I'll check regardless.

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[DaveN]

Sounds almost like the thermostat is running wide open. The faster you go the more cooling on the rad and the lower the temp. Did they change that along with the water pump? Does that guage jump instantly or slowly. Instantly and my theory is out the window.

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[spectre996]

It does rise/fall gradually, but it doesn't take real long. For instance, if I'm stuck in traffic on the interstate I'll be running warm. Once the traffice clears and I can resume highway speeds, my temp will be at 8 o'clock within 30 sec-1 min. I really need to check that last invoice to find out exactly waht was done. It was in the shop that time for overheating issues and squealing. The noise was a loose AC compressor bolt, but I can't remember exactly what was done on the cooling side.

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[flash]

it sounds to me like an airflow related issue - this could be due to either missing lower pans, a non-functioning fan, or a blocked radiator

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[spectre996]

The fan runs, both while and after driving, like normal. I'll check the 968 shop manual for which pans are supposed to be there. However, if one is missing it has either been missing since purchase 2 years ago or fell of while driving and I didn't hear/notice. I'd wondered about the radiator myself but didn't know where to start checking.

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[flash]

there should be at least 2 (the front apron and the center large plastic one), 3 if it's an early car (the third being a metal one)



first off, take a look at the radiator - look for stuff stuck in it, or the AC condensor in front of it

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[Cloud9...68]

I'd be surprised if missing pans alone would be causing such dramatic symptoms. I only have the front "bat wing" fan here in cantral Texas, and, now that I have a functioning thermostat, my water temperature is very normal, never getting to 10:00 oclock (though it probably hits 9:59 in the dead of summer near the end of a track session <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" /> ). Not that having more of the pans wouldn't improve my (or anyone's) airflow.



It just sounds like you have some sort of coolant flow problem - either a partially blocked radiator, or (hopefully) just a sticking thermostat. Start the car up, let it idle until the gauge gets to at least the 8 oclock position, and (carefully) put your hand on the fat radiator hose on the passenger side. It should be blazing hot -every bit as hot as the hose on the other side. If it isn't, you have a blockage. Let us know what you find.

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[flash]

because the problem is not related to rpm, and only speed, i tend to discount coolant flow issues - those should change with rpm - for example, if the problem went away at the same speed but in a lower gear, then i would suspect a coolant flow issue



it seems it is related only to airflow - this is why i would be looking at things that could be interrupting or hindering that - gunk in the fins of the condenser - gunk in the fins of the radiator - an animal in the way - a plastic bag stuck in there - fans not turning properly - things like that

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[Cloud9...68]

I agree to definitely check for any obstructions in the radiator fins, even before checking the temp of the return hose. I'm not sure I follow why the OP's problem still couldn't be restricted coolant flow, however. If his flow is compromised by, say, a partially stuck thermostat, this would decrease the efficiency of the transfer of heat from the engine block and head to the coolant. This would be offset somewhat by the having the air flowing more rapidly through the radiator, which would reduce the temperature of the coolant. This would happen at higher speeds, even if the rpm is constant.



In other words, the fact that the coolant is being cooled to a greater degree at higher speeds could be compensating for the decreased rate of coolant flow. But I hope it is as simple as something stuck in radiator. Many things could cause his symptoms - in fact, I'd be hard pressed to envision a scenario in which an engine wouldn't run cooler at higher speed. This is what makes hot running problems tricky to diagnose.

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[spectre996]

Well, this definitaly gives me a lot of things to check tomorrow. I'll let you know if I find anything.

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[flash]

i am presuming a lot in coming to the conclusion, but as stated, it definitely points me one way



what makes me discount a fluid flow issue is that the radiator is not subject to wind chill, or for that matter speed related issues - it really doesn't cool much faster at 50 than it does at 30, given the same rpm of the engine, and at a steady state of speed - the fans reach terminal velocity on high speed - no air can pass through faster than that, no matter how fast you drive - if the fans are coming on, and at speeds as low as are indicated, then there is likely not enough air flowing through the radiator



i would look for blockages in the airflow



i would verify that the same speed in different gears results in the same temperatures



i would verify that both of the fans come on at both low and high speeds, at the appropriate temperatures, and are on when at these speeds - with a stock switch, they should both come on low speed just above the 8 line and both on at high speed near the 10 line



barring a dead animal or a hefty bag in there, i tend to think that the fans are not doing what they should

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[S_Cal968]

Another consideration - has the ratio of coolant to water changed? If there' s a low concentration of coolant to water the temperature swing will be more erratic.

If the coolant is o-k, then perhaps there's a flow issue as mentioned...

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[Cloud9...68]

Hmmm... Interesting discussion, as ususal. Are you sure the air flow across the radiators levels off at moderate speeds? When my thermostat started sticking in the late summer of 2007, the surest way I could get the needle out of the danger zone was to drive faster, in the highest possible gear (maximum speed, minimum rpm). There were diminishing returns above about 60 mph, of course, but going from, say, 20 mph to 60 mph at roughly constant rpm (by shifting at about 2500 rpm) resulted in a significant reduction in temperature. My fans work perfectly, as you describe.



I'm not disagreeing that improperly functioning fans or debris stuck in the radiator could well be causing Spectre996's problems, but in my case, it was purely coolant flow related, and, as I said, my symtoms were similar to his. Also, Dave968Z (second poster in this thread) said that his car displayed similar coolant temperature response to speed when his water pump's impeller came loose from its shaft, which would have caused a coolant flow problem.



I guess the best advice, as is typically the case with hot running problems, would be to check everything, since the checks are relatively easy to do:



- First, remove as much stuff as you have to from the front of the engine (air box, primarily), and get in there and remove any debris you can find in and on the radiator and AC conedensor



- Start it up, and check the functioning of the fans, as Flash describes.



- Carefully put you hand on both radiator hoses. They both should be extremely hot.



By the way, Flash, I'm envious of your laser temp measuring tool, which I think you mentioned in another thread. Sounds like a very cool (sorry about that...) tool.

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[flash]

i love that tool - it has bee so helpful in figuring out what is doing what under the hood - between that and the half dozen other thermometers i use, i have been able to really see a lot



as for the "leveling off", i can only go by what i have going on with my car - i have a few things different in there though, which may well affect what is happening - i may get a chance to play around with this though on the 6th when i have other cars here



remember that i qualified the hypotheses with speed and rpm factors - the rule of thumb is that if the temp changes with rpm, but at the same speed, it's coolant system related - if it changes at varying speed but at the same rpm, it's airflow related

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[968TDG]

Ok, so I have a similar question about my cooling system. As a quick background, I live in Oceanside, where it ranges between 65 and 85 this time of year, and this ambient temperature range does not seem to be a factor. About 2 months ago I replaced all of the belts and water pump/thermostat. This of course involved draining and refilling the system with phosphate free coolant and distilled water. I then replaced the Oil filter housing gasket, and again replaced the coolant. The coolant is at the right level, I do not appear to be losing any, it looks clean, and there does not seem to be any air left in the system as I have bled it several times parked on an uphill with the heat on.

My temperature needle is always hanging just above the 8 o'clock white line when I am driving, but when I idle at a light, or after I exit the freeway, the needle will slowly start to wander up towards the second white mark. It never reaches this mark, normally only gets 3/4 of the way to it even if I am at the light for a few minutes. The engine does eventually regulate the temperature back down to the lower mark after a few minutes, though the fastest way to get the needle to go down is to start driving again. This is, however, driving in 70-85 F, so not very hot at all. It does appear that the fans are working, though I can't necessarily vouch for the speed. They do also come on once the car has been turned off as they should.

So the problem only seems to occur when the car is not moving, driving the car fixes the problem, and letting it idle for a long time will also eventually fix the problem. any guesses about what I should try replacing or troubleshooting?

Thanks
Phil

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[flash]

are the lower pans in place? the fans won't draw as much air through the radiator if they are not, and could lead to this

when you bled the system, was it hot? it needs to be above the thermostat point to work

do the fans both operate? at both speeds?

when you did the water pump, did you flush out the radiator?

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[968TDG]

Yes, all 3 of them are in place.

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