overheating issues

[qnzlvr]

91 Q. Cool air inside, resevoir full, no fluid showing under cap eventhough reservoir is full, engine over heated last night without me noticing immediately. I ran to operating temp this morning and steam escaped under plenum and maybe around radiator. How will i know if blown head gasket. Car runs smoothly, just overheats from I can tell. First guess is thermostat replacement needed.

[unknown007]

If it's coming under the plenum it could be a coolant hose underneath there.You wont have a leak because it'll just dump into the block's valley.Before replacing anything find out what the problem is and yes themorstat will need replacing.It isn't hard to do what so ever by easy if you remove the hoses that go above that area.The bolts if i remember are size 12mm.Make sure when you put the themorstat that the dot,where is says top, is pointing up and the aluminum cover is facing the right way or it won't line up.I found this out after thinking it was all the same.

If you are confused about what I mean go to my thread on the link I provided and look it'll show the valley and where the coolant goes.

zer...pdate

[Q45tech]

Q thermostats are of the fail open variety, thus causing an overheat is next to impossible. The usual failure is low or lack of heat and slow warm up in winter.

[qnzlvr]

Thx guys. I still have the question as to what would cause engine overheat without hot release to heater core. Durin the day of the failure I noticed alternating cool air and hot from my heater system. By the way, just reached 155k. Only real issues to now have been leaks under plenum, injectors, fuel pump twice. Have aux transmssion cooler and guides replacement completed. Also have had to clean MAF a couple of times. She's been a real charmer otherwise.

[qship96]

Low coolant level

No coolant flow {waterpump or belt failure}

[goody90q45]

I ran to operating temp this morning and steam escaped under plenum and maybe around radiator. How will i know if blown head gasket.

When you say the reservoir was full are you speaking of the radiator or the radiator overflow tank next to the battery? Sounds like you may have burst one the the under-plenum coolant hoses? Is there a lot of coolant in the valley?

Were you sitting at idle or in stop-n-go traffic when it overheated? If so, check the fan clutch for resistance. Remove the fan belt and the fan should be tough to rotate by hand.

As far as a blown head gasket....your engine oil would turn creamy white and your tailpipe would be billowing white smoke as if a pope had been elected.

[qnzlvr]

I was just in normal traffic when I noticed the temp gauge was all the way up. It was then I saw the steam billowing from the engine bay. From past experience with water pump failures I've always heard the bearings going out. This time there is no real indication nor obvious leaks. The gauge seems to stay pretty close to normal now after I filled the radiator directly. The motor sounds quiet but starts overheating as indicated by the steam flowing.
Modified by qnzlvr at 9:58 PM 2/24/2009

[MR. Q]

I once drove my Q on the freeway with a slipping transmission and the car overheated. Not a happy time of my life but 1 engine & 3 transmissions solved that problem LOL!

[Skibane]

Were you sitting at idle or in stop-n-go traffic when it overheated? If so, check the fan clutch for resistance. Remove the fan belt and the fan should be tough to rotate by hand.

If you removed the fan belt, the fan blades would be easy to rotate by hand, regardless of the condition of the fan clutch.

Leave the belt on, and run the engine with the A/C turned on until the engine is thoroughly warmed up. Shut the engine off and attempt to spin the fan blades by hand. If they're hard to spin and stop almost immediately after you let go of them, the fan clutch is working. If they're pretty easy to spin and continue to rotate a little bit after you let go of them, the fan clutch is not doing its job.

[Jesda]

My thermostat failed in a partially closed position. Not a common thing for the Q, but it happened to me.

If things havent been replaced, its time to do a full overhaul of your cooling system: radiator, WP, hoses, pulleys, belts, t-stat, fan clutch, fan blades, pressure cap. I ended up eventually replacing everything one by one until the problem was resolved.

Aftermarket water pumps, hoses, and radiators (I like CSF) are fine, but go OEM for the thermostat and pressure cap. The aftermarket thermostats, when fully open, will crush themselves because they are too large for the Q's thermostat housing. Also, the OEM thermostat is sometimes cheaper!

[Q45tech]

Failed in closed position can only occur if the unit was not changed every 60k [4-5 years] and the acidic coolant ate thru and destroyed the spring.

If you still have it I would love to see it for engineering anaylysis. We have never seen one in 14 years and hundreds of Q.

I should say we have never seen an OEM fail in that manner but aftermarket copies without jiggle valve have been know to fail in weird ways. Same with higher than OEM temperature range units.

[Jesda]

Failed in closed position can only occur if the unit was not changed every 60k [4-5 years] and the acidic coolant ate thru and destroyed the spring.

If you still have it I would love to see it for engineering anaylysis. We have never seen one in 14 years and hundreds of Q.

I should say we have never seen an OEM fail in that manner but aftermarket copies without jiggle valve have been know to fail in weird ways. Same with higher than OEM temperature range units.

I put it in the garbage about six years ago. I suspect it was well over 100k old. My 1990 Q's t-stat failed open as designed.

[3Q Jay]

replaced factory t-stat on blacq in Dec (had 09/94 date stamp). I had noticed slow warmup, and although it hadn't 'frozen' the rubber seat had split allowing bypass even when should have been normally closed.

[maxnix]

Just replaced my 1995 at 14 yrs. and 102K. Need to verify with thermometer, but looks like and according to the heat gauge, could have gone at least another 5 years.

Will post back when I get opening data.