# Odd cooling issue



## dougkehl (Nov 30, 2011)

Recently my QSW developed a weird cooling issue that I cannot seem to pinpoint. 

Over last weekend I went to Mk1Madness out in PA as I do every year, but I brought the QSW to camp in this year instead of my Mk1. The location of Mk1Madness is 2.5 hours from my house and I drove a solid hour and fifteen minutes before I hit the toll to enter into Easton, PA. That whole hour and fifteen minutes the car ran cool as a cucumber, but within a minute or two of leaving to toll gate the temp gauge started to rise to an uncomfortable level. This only occurred while I drove at highway speeds, if I slowed the coolant temp seemed to drop.

This car has a brand new aluminum radiator and fan, low temp fan switch, low temp thermostat, external oil cooler, heater core and the water pump was done maybe a thousand miles ago when I did the timing belt. And the coolant system has been thoroughly bled and their should be no air.

The car shows no normal signs of a blown head gasket which was my first suspicion, but there is no smoke. Not at idle, not under a load. There is no oil in the coolant and there is no coolant in the oil. It starts smooth while cold, starts smooth while up to temp and runs smooth as butter now that I've replaced all the lifters as of last week. I also suspected the new-ish water pump to be faulty, but I'm not so sure about that. 

I ran the car yesterday in my driveway just idling to see what it would do.. The gauge showed the temp getting kind of hot and then the fan kicked on for like 15-30 seconds like normal and then shut off and it repeated this consistently until I shut the car off.. The whole time the temp gauge was higher than normal. 

I know these use the same temp gauge as Mk2's and I've read plenty of those go bad randomly, but I'm not sure that's it because of the fluctuations the gauge is indicating.

Any other ideas as to why the coolant would rise in temp while driving, but not idling would be very helpful.


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## cuppie (May 4, 2005)

Do you have a complete, intact set of air ducts for the radiator? They're kinda-important on any car; very critical on a 5cyl. B-chassis car, due to the, ah, small radiator in weird spot. 
If you can't feed the radiator a sufficient amount of cool air, it can't do its job. 

I do remember mine having issues at highway speeds and higher (read: >80*F) ambient temps, until I made a new set of air ducts. Until I did that, though, highway runs generally necessitated turning the heat on.... 

What to use here? Corrugated plastic (like, sign material) is fairly easy to work with. Really nice (also easy to work, and looks a lot better) is the textile material that BMW is using for underbody panels these days. 
Any body shops in your area that service a fair amount of BMW? Ask - they may have an underbody panel or three for you to hack up.


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## dougkehl (Nov 30, 2011)

cuppie said:


> Do you have a complete, intact set of air ducts for the radiator? They're kinda-important on any car; very critical on a 5cyl. B-chassis car, due to the, ah, small radiator in weird spot.
> If you can't feed the radiator a sufficient amount of cool air, it can't do its job.
> 
> I do remember mine having issues at highway speeds and higher (read: >80*F) ambient temps, until I made a new set of air ducts. Until I did that, though, highway runs generally necessitated turning the heat on....
> ...


Currently I do not have them installed, but I do have them and I know that to be part of the reason it's running warmer, but it's never shown temps this high, with or without them at any speed even in 90 ambient temp weather. I just find it odd that I was driving nearly the same speed for over an hour with great temps and then all of a sudden I slow down for 10 seconds to pay a toll and then it nearly immediately started going up in temperature.

I'm going to inspect the water pump impeller and make sure it's not loose on the shaft. Because if it's slipping that could be part of the issue. I'm also going to pull out the brand new ducting I have for it and get it installed and take it for a spin and see if there is any change.


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## eurowner (Jan 26, 2002)

Verify running temps with an IR point and shoot thermometer on the radiator, upper hose, etc. The sending unit and or the gauge could be going bad.


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## dougkehl (Nov 30, 2011)

eurowner said:


> Verify running temps with an IR point and shoot thermometer on the radiator, upper hose, etc. The sending unit and or the gauge could be going bad.


Will do. 

I drove the car yesterday and today to work. The engine apparently was doing the same thing, at least that's what the gauge said, it was hot.. But I noticed one strange thing for about 5 minutes during my drive yesterday. The red light stopped blinking which started blinking all the time right as this issue started, cold or hot, didn't matter. I noticed when this stopped blinking the coolant level was pretty good so I proceeded to drive as normal.. No movement in the needle what-so-ever and then I got to work and let it sit and idle.. Nothing. No movement and the fan ran on and off as it should. 

I'm going to find a point and shoot thermometer though to verify it's not actually hot. I've got a few good gauges laying around and the sender is cheap so my fingers are crossed that's the issue.


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