Possible Bad News for my Q

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90Q45blue
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Hey Guys,

I'm writing to you because I need your help. As my sig says I have a 1990 Q45 with 251,000+ miles on the original engine. This summer, the following was done: new thermostat, radiator hoses, the under plenum hoses that were cracking were replaced, O2 sensors replaced, cooling system flushed and refilled with 70% water, 30% antifreeze, bg44k used, plenum removal and cleaning of throttle body etc.

Here's my problem. So in Lawrence last week it got up to as high as 109 degrees outside. I already posted an overheating problem that is now a little buried but anyway:

Last Monday I was driving my brother home from Wal-Mart when my temp gauge started rising. By the time we got near his dorm (1 minute later), it was a high as it could go. I immediately shut the car off and left it parked. Later that night I picked it up, drove it home and it had no overheating issues. The only peculiar thing was that when I parked the car at my apartment, when I shifted in park the rpm's shot up to 2100 and would not come down. I shut the car off and vowed not to drive it until the temperature cooled down.

Today it is 68 degrees outside, I went to go do laundry and on my way back to my apartment, it started to overheat again. Amazingly, this was as I was in the parking lot so I parked it. First problem was the rpm's shot up to 2500 and started fluctuating between 1700 and 2500 and would not stop. I turned off the car and popped open the hood to see the engine smoking a little. I have not gone back out to check oil and antifreeze because it is still too hot.

So the question is, what do you guys think is wrong? I'm thinking this may spell the end for my car but we shall see.

Please help :(

Nick


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PalmerWMD
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Nick:

Off-the-cuff:

Does your car have more blue smoke now?If not, there was likely/hopefully no mechnical damage.

The waterpump + radiator are original?

replace those and overheats should stop.

About your weird rpms, are likely damged sensors causing them ( I hope.

Fred...:)

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elwesso
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Have the rad checked out........ And the water pump.....

One decent way to check the water pump is to start it with the rad cap off...... It should pour out.... dont run it more than a few seconds.......

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90Q45blue
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There is no blue smoke so hopefully you're right Fred and it is not something mechanical. The water pump and radiator have been replaced but it has been at least 100k since that happened. Also, do I need to check the ECU to see what sensors are causing the rpm's to go nuts? What else might be causing this?

Thanks,

Nick

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elwesso
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For the RPM deal, you could try and unplug the battery cable for 24 hours...... it will delete all ECU codes, so that might help something.......

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elwesso
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Even though its unlikely, Id still check the Tstat....... Just replace it again, its only a $10 part.........

Since the rad and waterpump are all relatively new.......... Everything seems to point to this (in my view)

When did it start doing it..... Did it just start doing it after you let it sit for a while (you did, didnt you??)

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90Q45blue
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It started doing this when my car overheated last Monday. When I shut it off that time the rpm's shot up to 2100.

Nick

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elwesso
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I was referring to this whole overheating thing........

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90Q45blue
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Oh, it started last monday. temp outside was 109

Nick

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elwesso
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And it was just fine before then??

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90Q45blue
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Yep. 3 weeks after all the above-mentioned work was done to it...including a new tstat.

Nick

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Man...it sounds like a classic thermostat problem to me...

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elwesso
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Yep.......

Its worth a try........ Its very possible you got a bad Tstat........ Unlikely, but its seemingly becoming more and more evident that is the cause of the problem.........

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Q451990
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I wonder if all of the work and the new coolant (maybe a chemical flush in the process?) loosened up some junk that clogged the radiator. I'd replace the t-stat first, but I'd sure take a close look at the radiator too.

Heath

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make sure theres no air in the coolant system

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90Q45blue
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I'm calling my mechanic tomorrow morning. I'll probably have the car towed for someone to look at it. Hopefully it's just a faulty Tstat and Joe can hook me up again. That radiator is too expensive.

Any other ideas on the rpm's? I am baffled by this one.

Nick

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You must read the coolant temp with Consult to see what ecu is seeing [don't ever rely on inside temp gauge if it has ever risen above 3 o'clock.The inside gauge sensor will not read steam it must be surrounded by coolant!!!!!!!!!!!!!!!!!!!!!!!!!!!!

100k or more since rad replacement, how long since the rad was cleaned of all the junk between it and condenser? belts......water pumps don't fail they just leak out the dribble hole, FIRST.

When the Q goes beyond 220F weird things start happening and ecu is just trying to get your attention..........rise and fall rpm.

109F might be 120F in traffic hot asphalt. Obviously only a brand new radiator with no air restriction can meet this specification.

Have the knock sensors checked [with Consult] as a combination of ignition retard from hot coolant [215F would be 5 degrees] and KS failure another 5 degrees would cause the surging at idle.

Atlanta has had the coolest July in 34 year and August was not far behind.........so I can't force duplicate the problem/symptoms.

What is condition of electric auxillary cooling fan and its switch [test it]! Fuse condition!Same with plastic fan and clutch.

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90Q45blue
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Thanks for the info Dennis. I'll have all that checked out. I did replace the plastic fan and clutch 3 weeks ago. I called my mechanic and he said it might be that Tstat which is what most of you seem to think it is. THat's what I'm hoping anyways. The other thing he said that made me cringe is that it might be the head gasket. :(

What do you think the chances are of this?

UPDATE: I'm having my car towed today (via flatbed of course) to Lawrence Automotive Diagnostics. They seem like stand-up guys and one tech there has worked on first-gen Q's before (about a dozen of them). It's no T3, that's for sure but it's the best I can get here in town. I'll let you know what they find out. What else should I have them check besides what's listed in this thread already?

Thanks,

Nick

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Head gasket (or warped head) is a possibility based on the overheating, but very often it's accompanied by other symptoms, like white exhaust smoke, oil in coolant, coolant in oil, etc. Your tech will probably vacuum check the coolant system first. Let's hope it's "only" failed knock sensors, even though those can be costly in both parts and labor.

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90Q45blue
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Well just got word from the shop that I had a plugged and leaky radiator so I'm replacing that. They said they checked out the other possibilities and everything checked out fine so far. There was no sign of coolant in oil or vice versa and no discolored exhaust. I will have them check the ECU for good ol code 34 and see if knock sensors are in my near future.

Thanks guys!

Nick

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If your rad only lasted 100k you are not performing adequate maintenance........must be missing those annual simple rad drains [3-4 quarts] and refills to replenish what ever additives are depleted and the 30k flush and system refills.

It's not just the replacement cost you are trying to defer but the engine health from out of range temperatures and the engine varnish from over heated oils.

If the interior gauge EVER goes above 3 o'clock you need an oil/filter change ASAP! Consider an ATF replacement as the cooler will turn into an ATF heater fast.

The systems are so interrelated and the chain of events so expensive.

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90Q45blue
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Dennis, I took your advice and did an oil/filter change and replaced the ATF. Got the car back today and everything seems to be ok. My only problem is this: when I have the A/C running and I shut off my car it sounds like something is bubbling under the hood and then settles. What do you think it might be?

Nick :confused

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90Q45blue
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bump:

I'm pretty nervous about this problem. Does anyone know what could be wrong? Or am I worrying over nothing?

Thanks,

Nick

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Q451990
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Does it sound like a sloshing sound in the dash? If so check out this thread.

http://www.nissaninfiniticlub....34433

Heath


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