1995 3000gt overheating need help

[hollydolly]

I have a 1995 3000gt sl. When im on the freeway running at 80 mph and maintaining that speed it starts to overheat.I can reduce my speed and it starts to cool down I can also turn heater on high and that cools it down I cant hit the exit ramp and by the time I get stopped at the end of ramp its cooled back down.I can start it and sit with it running and it never gets hot.If I stay below 55 I never have any overheating its only when I increase and maintain 75 or faster I have a problem. Also when it was hot outside I turned my air on max cool one day and it got hot real fast.So to fix that I just didn't run my air any more. then a few months went by and this started to happen.50mph and slower its fine.But at freeway speed limit it starts running hot. Only with increased speed to the engine does it start getting hot.

HERES WHAT IVE DONE SO FAR TO ATTEMPT TO FIX OVERHEATING

FIXED A STOPPED UP CATALYIC CONVERTER BY WELDING A PIPE TO BYPASS IT

REPLACED TIMING BELT
REPLACED WATER PUMP
REPLACED SPARK PLUGS
TUNE UP
REPLACED THERMOSTAT
REPLACED RADIATOR CAP
REMOVED THERMOSTAT COMPLETLY
WIRED FANS DIRECT
FLUSHED RADIATOR
FLUSHED HEATER CORE
disconnected HEATER CORE TO BYPASS IT
FLUSHED THE MOTOR BLOCK
REPLACED TOP RADIATOR HOSE


ONLY THING I HAVENT DONE THAT I CAN THINK OF IS

REPLACE RADIATOR and bottom radiator hose
REPLACE HEAD GASKET-I HAVE FILLED RADIATOR UP ALL THE WAY WITH THE CAR RUNNING AND RADIATOR CAP OFF SO WE COULD SEE IF IT BUBBLED OUT LIKE IT DOES WITH A BLOWN HEADGASKET BUT NO BUBBLES.

someONE TOLD ME TO TRY LIQUID GLASS THRU IT.iS THAT A GOOD IDEA .I HAVE THE BRAND NEW RADIATOR BUT HAVENT INSTALLED IT YET .IF I RUN LIQUID GLASS THRU IT AND IT STOPS UP THE RADIATOR THEN ILL INSTALL THE NEW RADIATOR.I THINK IF I TRY LIQUID GLASS I NEED TO TRY IT WITH THE RADIATOR THATS IN IT NOW.

The car runs great.Scary fast. it doesn't run like you would think one with a blown headgasket would be running.

could it just be a part of the head gasket system and not all of it? CRACKED HEAD MAYBE=IF SO WILL LIQUID GLASS FIX IT

Any info as to what I need to check.That I havent
im a thousand dollars in and still haven't found the cause.

car has 120000 miles on it.

sitting still or stopped at stop light no overheating

only when im up to speed limit and maintaining that speed is when it gets hot and slowing down brings temp back to normal range

its a dohc 5 speed manual 3000gt sl

ANY HELP OR SUGGESTIONS YOU HAVE PLEASE TELL ME

WOULD THE STOPPED UP CATALIC COLNVERTER DONE DAMAGE TO THE HEADGASKET.iM NOT SURE HOW LONG I RAN WITH COMPLETELY STOPPED PROB A WHILE, BECAUSE IT HAD BJURNT ALL MY SPARK PLUGS UP.. IT HAD GOTTEN SO HOT

[hollydolly]

Any one going to read this i need some help

[Crvett69]

did you blow out the fins on the radiator and ac condenser in front of it, might be bug and debris plugged. is it using any water and if you take your oil fill cap off does it have a white residue on the bottom of it?

[MikeCStig]

It does sound like a cracked head or a head gasket leak, not necessarily blown, just leaking. If there is a leak in the head gasket, it will only get worse and eventually it will blow. If the head is cracked, liquid glass would only work as a band- aid type fix, it's not a permanent solution. It would hold for about a year and that's if you're very gentle on the engine; lower revs and no burying the throttle, which in a 3000 GT I'm sure is always tempting. The only permanent solution I can see here is to remove the head and check it very carefully for cracks. When I say carefully, I mean use a magnifying glass in the best possible lighting. If the head is cracked, you'll have to get a new one, and of course when a cylinder head is removed, the old head gasket cannot be reused.

[hollydolly]

no I haven't im replacing the radiator today and hoses.and then will see if it still does .it. not using water and no white residue. got another question this morning I get in cr and drive it for a while and when I would at stop light it started idle reving.i didn't have my foot on the gas pedal but the idle was reving up and down 1-3 rpms at a complete stop by itself any idea.

[Stealthee]

The self revving could be related to the ISC (idle servo control)

[hollydolly]

idle server control-do I need to replace it.
it just startedthis 3 days ago and it happened suddenly. when im at a stop sign idle surges up and down between 2 and 3.when first start when its cold it doesn't surge but when it warm to operating temp that's when it starts surging.when I take my foot off gas pedle and coast I can hear it surging..no check engine light is on.

[Stealthee]

You can check the ISC to verify its bad, or good. All you need is a multimeter.

It has 6 pins oriented in two rows of 3.

123
456

What you are going to do is check resistance between the pins 1 and 2, 2 and 3, 4 and 5, & 5 and 6. You are looking for around 32 ohms. A bad ISC will result in one or more of the readings likely being 0.

If it is verified as bad rockauto sells the ISCs, PN AC99 for around $70.

[hollydolly]

where is the isc located. where do I look when I raise the hood?. also what about maf cleaner.should I do that first? do u think adjusting the BISS{base idle set screw} to see if it helps is a good idea or do I just need to leave it alone?

[Stealthee]

ISC is on the side of the throttle body.

stealth316 should help you out here http://www.stealth316.com/2-isc-iac.htm

As for adjusting the BISS it might help, but its only a band-aid to the actual problem. It's not a solution. The car will eventually adjust itself and be right back to square one. I would personally leave it be.

[hollydolly]

I need to buy a ac/alt tensioner pulley.i would say its the lower one.since it sits on the bottom side of motor.mine is seized up.any info on where I can order one . And part number I type in to pull it up to place order.how much are they.thanks hollydolly

[Stealthee]

The $101 at 3s warehouse is probably the cheapest you are going to find. They are $125+ at any other place.

[Crvett69]

e-bay has them for sale for about $80 with shipping for a mitsubishi one. if same belt runs the alternator you can get a aftermarket one at autozone for about $40
here is the e-bay one
http://www.ebay.com/itm/Alternator-A...9xEBuA&vxp=mtr

[Stealthee]

Originally Posted by Crvett69

e-bay has them for sale for about $80 with shipping for a mitsubishi one. if same belt runs the alternator you can get a aftermarket one at autozone for about $40
here is the e-bay one
http://www.ebay.com/itm/Alternator-A...9xEBuA&vxp=mtr

That's not the right one. The listing is in error. That pulley is an idler. The pulley she needs is the one that says Ref 55-430.

[hollydolly]

thanks.another question I read on here someone had bypassed this tensioner altogether.Can u run with out one? explain if that's possible.