Bizarre Overheating Issue
04-12-2004, 03:13 PM
#1
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Join Date: Nov 2002
Posts: 127
This is a copy of my post on the Other Forum. I will be checking both regularly for replies.
Most of you guys know I am an oldtimer at rotaries but this one has me stumped. This is going to be a long post, but I am going to give you all the details I have.
I just had a more radical street port engine built and installed. I have the AST bypass modification (grafting a 2nd gen filler cap onto the OEM filler cap position) which has always worked well for me.
After a number of false starts the engine fired over and I took it out for a test drive.
I have three (yes 3) temp gauges, the stocker with the sensor at the OEM position near the oil filter, the Power FC commander with the stock sensor at the OEM position on the coolant neck, and an Intellitronix digital with the sensor mounted in the coolant neck just below the .9 bar cap.
Temps reported by all three gauges increased to around 210 F (99 C) going up the mountain but stabilized at about 85C 185 F tooling around town and up to 80 mph extended driving. After about 45 minutes I returned to the shop and burped the system which took about 8 oz of water. I then took the car out again but within 2 blocks, the aftermarket gauge started climbing into the 210s along with the Power FC going above 100, I flipped on the fan mod switch and immediately noticed the OEM gauge approaching the 3/4 hot mark (no warning light yet and not over the hot line). I shut it down and cooled off the system for about 1/2 hour. Checking the peak holds on my aftermarket gauge and Power FC it appeared that the temps reached 235F or around 112C. I opened the cap and added another 8 oz of coolant. I drove back to the shop where the car was again cooled and a few more oz of water were added.
My mechanic believed that the problem was because I have a stock radiator....we disagree strongly, since I have had the radiator in this car since day 1 and drove the hell out of the first engine with no negative results.
Long story short----I took my car as is and trailered it the 300 miles back to my house.
Here is where it gets weird. Testing the car in my driveway, I now notice that the PFC commander and the aftermarket gauge read similar temps (between 180F (85C) and 200F (95C)) but the OEM gauge is still going above normal. I would gladly believe the OEM sensor is screwed up, but I know these 3rd gens are much more tricky than that.
Finally, after warmup there are no bubbles appearing in the filler neck--- The system hold 14 psi with no leakdown as tested by a mityvac test kit.
I believe there is at least a possibility that I have an air pocket stuck near the OEM Gauge sensor at the back of the block and it is reading the high localized temps. I am open to other thoughts and all manner of cures that I should try.
Thanks
Jeff
Most of you guys know I am an oldtimer at rotaries but this one has me stumped. This is going to be a long post, but I am going to give you all the details I have.
I just had a more radical street port engine built and installed. I have the AST bypass modification (grafting a 2nd gen filler cap onto the OEM filler cap position) which has always worked well for me.
After a number of false starts the engine fired over and I took it out for a test drive.
I have three (yes 3) temp gauges, the stocker with the sensor at the OEM position near the oil filter, the Power FC commander with the stock sensor at the OEM position on the coolant neck, and an Intellitronix digital with the sensor mounted in the coolant neck just below the .9 bar cap.
Temps reported by all three gauges increased to around 210 F (99 C) going up the mountain but stabilized at about 85C 185 F tooling around town and up to 80 mph extended driving. After about 45 minutes I returned to the shop and burped the system which took about 8 oz of water. I then took the car out again but within 2 blocks, the aftermarket gauge started climbing into the 210s along with the Power FC going above 100, I flipped on the fan mod switch and immediately noticed the OEM gauge approaching the 3/4 hot mark (no warning light yet and not over the hot line). I shut it down and cooled off the system for about 1/2 hour. Checking the peak holds on my aftermarket gauge and Power FC it appeared that the temps reached 235F or around 112C. I opened the cap and added another 8 oz of coolant. I drove back to the shop where the car was again cooled and a few more oz of water were added.
My mechanic believed that the problem was because I have a stock radiator....we disagree strongly, since I have had the radiator in this car since day 1 and drove the hell out of the first engine with no negative results.
Long story short----I took my car as is and trailered it the 300 miles back to my house.
Here is where it gets weird. Testing the car in my driveway, I now notice that the PFC commander and the aftermarket gauge read similar temps (between 180F (85C) and 200F (95C)) but the OEM gauge is still going above normal. I would gladly believe the OEM sensor is screwed up, but I know these 3rd gens are much more tricky than that.
Finally, after warmup there are no bubbles appearing in the filler neck--- The system hold 14 psi with no leakdown as tested by a mityvac test kit.
I believe there is at least a possibility that I have an air pocket stuck near the OEM Gauge sensor at the back of the block and it is reading the high localized temps. I am open to other thoughts and all manner of cures that I should try.
Thanks
Jeff
04-12-2004, 03:18 PM
#2
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Join Date: Jul 2001
Location: Tulsa, OK
Posts: 3,346
Might want to get thermometer and veryfiy the coolant temps by sticking it directly into the coolant.
Also: might not be a bad idea to pull the thermostat and test it in water to make sure it opens at the correct temperature. Could easily gone bad and sticking.
Also: might not be a bad idea to pull the thermostat and test it in water to make sure it opens at the correct temperature. Could easily gone bad and sticking.
04-12-2004, 03:30 PM
#3
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Join Date: Nov 2002
Posts: 127
Originally Posted by 94touring' date='Apr 12 2004, 12:18 PM
Might want to get thermometer and veryfiy the coolant temps by sticking it directly into the coolant.
As to the thermostat, yeah that has me worried also since the temps behind the t'stat would be higher (like at the OEM gauge sensor) and cooler in the filler neck. Good call and I will check that too.
04-13-2004, 07:25 AM
#5
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Join Date: Nov 2002
Posts: 127
Originally Posted by Fd3BOOST' date='Apr 12 2004, 07:08 PM
The thermostat needs to be replaced.
04-13-2004, 08:37 AM
#7
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Join Date: Nov 2002
Posts: 127
Thanks Pete
I am in the process of replacing the T'stat with a new one (again) and vacuum filling the cooling system. My daughter's fiance' (who is an Audi certified tech) suggested the vacuum fill. According to Audi, anything less than vacuum filling will leave a small amount of air trapped somewhere. Funny I never heard of such a system but Ben assures me all the dealerships are using them now.
Regards
Jeff
I am in the process of replacing the T'stat with a new one (again) and vacuum filling the cooling system. My daughter's fiance' (who is an Audi certified tech) suggested the vacuum fill. According to Audi, anything less than vacuum filling will leave a small amount of air trapped somewhere. Funny I never heard of such a system but Ben assures me all the dealerships are using them now.
Regards
Jeff
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