I know this may be a silly question, but wanted to run it by you guys...

[telijah]

I'll start with the question and then give the background, in case someone does actually know this: Is there any way possible that a failing DISA could affect the operation of the thermostat?

OK, I will start about a year and a half ago, at the beginning of relevant info. I started throwing a code for the exhaust cam shaft position sensor. Around the same time, I noticed my car took a while to warm up and was throwing the code that indicated I had a t-stat stuck open. Both are no biggie yet. I had a shop in February replace my alternator because I am lazy, and he clued me into a very very small coolant leak in the radiator. It required me to maybe put in a pint of coolant every month or so. Still, no biggie for me.

Starting last month, I started getting very rough idles and if I idled rough long enough, it would misfire when accelerating. I figured "welp, that cam shaft pos sensor finally needs to be replaced". So, since the head was stripped on the screw for the CPS, I had the same shop swap out the sensor, but he tells me that wasn't the source of my idle problems. He said the gasket for the DISA was bad/causing a vacuum leak. I took it home to fix it myself, but upon pulling the DISA out, the flap was falling apart, so the whole thing needed to be replaced.

So, Tuesday, I finally replaced the DISA, which definitely fixed my idle and improved the way the car acted between shifts... I'm loving my car again. I cleared the codes and went on my way. That night, the temp went slightly past 12 oclock, so I pulled over, added coolant, and continued.

Since then, I have not thrown any codes again, not even the t-stat code, and I am noticing now that the temp gauge on the dash is going to 12 oclock much quicker... as if there was never a problem.

I am usually the one to tell people that cars just don't fix themselves, so I am wondering, if anything I had recently done, may have also been causing the temp not to reach normal operating range?

[brettbimmer]

I don't know the answer to your question, but post E30 era cars have their temperature gauges "dampened" from the factory, so that it takes larger fluctuations in engine temperature to be reflected on the temperature gauge. I heard this was done to help keep unschooled owners out of the dealers when their cars ran at different temperatures due to seasonal temperature changes, and so our cars run at 12:00 unless we have a good variance from normal operating temperature. Hope this is a helpful tidbit.

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[telijah]

Well that I am aware of, but until Tuesday, it would take probably 15 minutes of driving for it to reach 12 o'clock. I wonder if it has to do with me filling it up that night... Normally, when my car needed a coolant top off, I did it while the car was cool. I would still put the key to the on position and turn the temp on the air con to 91 and top off, but that night, the car was already warm and I turned the heat on while driving to try and bring the temp down. So I wonder if filling it, with the heat already on and the car warm, maybe had something to do with it. To me, that makes no sense, but am interested to hear if it actually does.

[Hornung418]

Replave the radiator and all your troubles will go away. That's what my situation was like. I couldn't find the leak on the radiator until I was under the car looking at ut with the fan off. The whole bottom row of fins was seperated and the leak was apparent. They are cheap at AutohausAZ with free shipping on items of that size. Good chance to replace the Thermostat and WP while you're in there.

GS3 + TT4

[telijah]

A replacement radiator has been sitting in my apartment for several months now, I just need to stop being lazy. Still, cannot figure out why the car is seemingly reaching operating temp in a normal time period now, when for months, it would take a decent amount of driving, and the code that was being thrown has also stopped.

[Hornung418]

Hmm that is interesting. But even at 120k and 14 years my radiator was FUBAR. The replacement definitely solved my mystery leak though. At first we thought it was the WP. so I had them replace it again even though it was a Stewart and had less than 6 months operating time on it.

GS3 + TT4

[LivesNearCostco]

It is possible the thermostat was stuck open for a while and now is working properly. Or the wire to the thermostat was disconnected? Or coolant temp sensor was bad or had poor connection to harness plug, and now it's okay?

[telijah]

It is possible the thermostat was stuck open for a while and now is working properly. Or the wire to the thermostat was disconnected? Or coolant temp sensor was bad or had poor connection to harness plug, and now it's okay?

As coincidental as it sounds, one of those is the only conclusion I can come to. On the plus side, doing the DISA swap was the first bit of DIY I've done outside of regular maintenance in quite some time, and now I have the bug to go ahead and do the radiator and some other items I've been sitting on.