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Discussion Starter · #1 ·
Bear with me, it's sort of an involved story. I have a yellow '90 Corrado G60 with a bone-stock powerplant. And I have some strangeness in the cooling system that is driving me crazy.
It would appear to work 'normally' during the daytime. Temps would climb in traffic or when I was sitting at a stoplight, then drop as I got up to speed. Ranging from 205 to 225, as indicated by the water temp gage. I tend to trust the gage, since I see similar ranges mirrored in the oil temps (according to the MFA).
But at night, it's a completely different story. One would think that at night, with cooler air, the car would run cooler, right? Not in this case. In fact, the temps would rise right up to a hair under 230 and stay there. And I mean stay, like the needle was nailed to the gage face. It could be 80 MPH down the highway, slogging through city traffic or stopped at a light, the needle never moved. Mind you, I do the bulk of my driving at night, because I work a graveyard shift. So I go in around midnight and am coming home early morning.
A friend of mine (who owns a Passat GLX VR6) suggested my thermostat was behaving badly. I figured it was worth a look-see, so I pulled apart the cooling system (we all know how fun it is to get to the t-stat housing) and tested the t-stat in a pot of water. It opened up at 195, although I suppose I can't vouch for the accuracy of the candy thermometer I used. Still, it opened and closed when pulled out of the water and put back in. I went off to put it all back together and figured as long as I had the system drained, I might as well wash it out (I didn't have time for a complete flush) and refill with fresh coolant. I did this, flushing water down the expansion tank and upper radiator hose until it ran clean. Refilled with 35/65 mix and went for a test drive. Temps seemed quite dandy, but it was daytime...
Two days later, after I got a replacement upper radiator o-ring from the local dealer (the old one started hemmoraging after I disturbed it), I went out for a drive again. Good temps in daytime, so the real test came at night. Tripping out with a friend, I find I'm out of luck! Temps are cooler by about 10 degrees, but the gage still remains firmly nailed to the 215 line.
Before someone suggests a 185 or 165 thermostat, I have one more little oddity. On the way back home, temps acted the same as always until I departed the freeway for a little 'fun' detour. Temps began to flux on the city streets, then as I rolled down a long hill back to the freeway, they dove! They actually fell under the 195 line on the gage. But I figured once I got back on the freeway, I'd see things go back to normal. Not this time! I pulled 195 water temps and 212 oil temps all the way back home. It was fabulous! I tried to repeat the behavior on the way home from work this morning, and no dice. Couldn't do it. I even sat and idled in a parking lot to let the temps rise enough to trigger the radiator fan. When I bounced back on the freeway, the temps fell under 210 for a little bit, but then crawled back up and stabilized at 210.
My Passat friend still thinks it's the thermostat, and I'm thinking it is too. Either sticky or flaky or just not working right or whatever. But I'd like a third/fourth/fifth opinion before I crawl back under my car and take off the PS pump bracket and... you know the story.
Any ideas? I'd love to hear 'em. ^_^
James
 

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Re: My cooling system is possessed! (Kerosel)

when is your low temp and high temp fan coming on btw?
Sounds like you have air pockets in the coolant system or (gasp) blown head gasket.
You did replace the t-stat right? I mean after taking it out and all that.. if not go buy a 180F thermo, and check your radiator fan-relay-switch so make sure the fan is coming on at the right temps.
 

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Re: My cooling system is possessed! (mrkrad)

maybe also go get a antifreeze tester and make sure that it can handle the weather you have. I had the same problem all because the mixture wasnt strong enough. It would happen more in the night time because it was colder. The rad would freeze and wouldn't let the coolant flow. Did you have heat when all this was happening?
 

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Discussion Starter · #4 ·
mrkrad: Ugh, I've got my fingers crossed against a BHG. It doesn't seem to have the traditional symptoms, but this is a non-traditional car. You reminded me of something: I think there's trouble in my low-speed fan circuit, because the fan comes on around 230 (indicated) and shuts off at 215. While on, the fan runs at the same speed as when the A/C is on, which is the high speed, right?
Tomorrow after I wake up, I'm gonna shoot out the low-speed system. It had been giving me trouble before (always on) and a previous mechanic's solution was to pull the relay. Relay replaced by the most recent mechanic, but apparently there's still something wrong.
And no, I didn't replace the t-stat... It started out as a routine investigation and then turned in to a flush and a 'what else is wrong?' once I found the stat seemed to be working right. Now that I know what a pain it is to get to, I'm regretting not replacing the stat while I had the system open. The stat is unknown to me, but it's at least 3 years old (as long as I've owned the car). For all I know, it's the original one. ^_^
djbrandot: That's an interesting suggestion that never occured to me, but I forgot to disclose I live in Southern California. Only once in the last 6 months did the nighttime lows drop under 40 degrees. I'll keep radiator freezing in the back of my mind, but I'm not sure I need to worry about it. Speaking of which, the radiator is also 3 years old. It got replaced after I had a little head-to-head with a Lexus shortly (6 friggin' days, the Friady before Driver's Fest 2000) after I bought it.
Thanks guys. I'll come back with the results of my tests if I'm still stumped. At this point, replacing the t-stat is pretty much a given. I just want to figure out if the thermoswitch is faulty so I can order a new one along with the stat.
James
 

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Re: My cooling system is possessed! (Kerosel)

Kerosel, you mentioned early on that the night time temps were different to the day temps. I have seen temp gauges that change when the lights are turned on and off. This is happening to a mates Rallye at the moment. He ignores it but the needle does move and the MFA changes too???

I am not suggesting you kill the lights at speed but maybe turn the lights on/off and watch what goes on.
Oh yeah, I don't know the cure!! Maybe a bad engine earth or something weird.
Gavin
 

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Re: My cooling system is possessed! (H100VW)

there's trouble in my low-speed fan circuit, because the fan comes on around 230 (indicated) and shuts off at 215.
this is wrong. With a low temp fan switch. the slow speed should come on at 180F. I tied the slow and high speed together on my cars because low speed is useless in the summers here. If your fan switch is functioning and fan low speed is functioning i would do that.
Better to keep it cool than get so hot! You never want to exceed 190F coolant temps, if you do, you must take action, be it oil cooler, new radiator, better fan, whatever.
These cars were designed to run at 190F always, once they age they can go above it, but you are just making your engine less efficient, and by a good bit, as the tendency to detonate goes up.
I'd test your fan switch, and fan, theres no reason at all the high speed only comes on at that rate unless theres an electrical problem. I had a bad fan switch like this, it was melted down. Replaced it and bam fan comes on at 180F.
 

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Discussion Starter · #7 ·
Thanks for all the replies...
H100VW: That's been brought up too... about floating grounds and other electrical effects. There has been once or twice where I've turned on the headlights and sworn the temperature changed, and yet I can't get consistantly repeatable results. One of my other pet theories was the voltage regulator for the instruments is failing because the fuel gage reads a little high (off by about 1.5 gallons), but the offical repair for a failed VR is 'replace the whole instrument cluster'. Foo.
The other day, I tried really loading down the electrical system. A/C, headlights, blower on #4... The needle didn't seem to move (or if it did, it did very little). Again, when it does move after an electrical load change, I can't get it to do it twice in a row.
mrkrad: I know that's wrong... I wonder if flow problems would contribute to this? From what I can see (or think I see?) is the thermoswitch is located in the post-cooling area of the radiator, while the gage sender is right at the outlet from the engine block. Could it be the temp coming out of the engine really is 230, but it's just hitting 190 or 195 (assuming my thermoswitch is off by some) post-radiator? Either way, it doesn't change the fact the coolant coming out of the engine is hotter than usual.
By the way, I tested my fan by hooking it right to the battery. All circuits appear normal, what I was seeing really was low speed. As for people who tied their low and high circuits together, how can you stand that? My high speed is almost scary. It sounds like a blow-dryer and pushes hurricane-force winds! Someone commented their fan came apart while on high speed, and I can see why. I'll keep my low/high split for now... low pulls enough air to cool things down.
New stat on the way... I split the difference: The original was a 195F, the stock replacements are 87C (about 188F?) so I went with one of those. When I do the chip-swap and other performance upgrades, if it runs hot, I'll put in a 180F thermo. After all, I'm becoming an expert in getting to the thermostat! ^_^
Thanks again for all your replies and help... I'll keep you posted.
James
 

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Re: My cooling system is possessed! (Kerosel)

I just found my old cooling system inefficient in high heat. I'll take the chance of ruining a fan motor, than warping a head. in the hot georgia summer, i always end up using the high speed (when wired correctly).
This goes to a more deeply rooted problem. Maybe your radiator is tired? Maybe you should get a real oil cooler (that water/heat exchanger is probably more geared for emissions than cooling, imo).
I'd place money on a new radiator giving tremendous gain. I know on my old 5.0 rustang, after about 10 years, it had major overheating problems. Quick trip down to the pep boys and $50 later, problem solved. Of course when the motor was boosted up to 500hp, that radiator proved inefficient and a very expensive aluminum one, i forget the name, was necessary.
If my car runs hot this summer i'll probably do the radiator, then look at those cool hallmotorsport oil coolers.
Just gonna have to buck up and spend the $$ and i've got confidence with both of those solutions i'll see a dramatic improvement in cooling.
I had this thought in the back of my head, btw, to have the ecu control the cooling system too. It is possible for me to program the ecu to fire a relay when conditions are met to maintain an optimal temperature. Would this be better than what we have now? Who knows, but i think an ecu might be able to weigh conditions with forethought rather than passively waiting for the temps to rise then turn on the fan?
Or maybe i'm just dreaming
 

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Discussion Starter · #9 ·
I just wanted to report... I swapped in a new 87C Whaler therm two days ago, and Zonker is runnin' cool as a cucumber. Stays right at 195 when cruising the streets and just slightly higher when on the freeway, but it stays there no matter 65 or 95. Oil temps are down too... even when flying a 95 run chasing a Saturn while going in to work tonight, I only saw 198 water 224 oil... And the oil I can live with, because I was turning 4250 on the engine, and before I was getting 232 oil temps cruising at 70.
So now the next project is to investigate the thermoswitch, because it still waits for higher temps before it kicks in... but I did try idling it with the A/C on to run the fan, and the temps sank back down to 195, so when the fan turns on at the right temp, it'll be just fiiiine.
Oh yeah, I can't get over the perforance change now that he's running cooler. The night after I changed the therm, I got behind a large pickup at a light, and he roared away at the green and I thought 'Oh no you don't' and I stomped on the loud pedal... Man, Zonker just flew off the line. Chirped the tyres over the crosswalk and was at 5.5k RPM before I realized it. Sounds nice and doesn't feel like it's labouring to take off in a hurry. Probably partly because I'm running 87 fuel, but I'll change that once I'm making some more money.
Thanks for all your help, guys. I appriciate you being here on the Vortex when I run into mental brick-walls. ^_^
James


[Modified by Kerosel, 4:52 AM 2-7-2003]
 
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