OK heres the skimnny.
86 coupe
I run a ZZ4 motor with TPI - probably not important. It is essentailly a track car - but I do keep it street legal.
Right now I have this intermittant cooling issue.
2 weeks ago I take the car out - iut heats up to 250 degrees within 5 miles - It's gotta be water pump I fiigure - but no sign of pump failure.

so in order to diagnose:
3 days ago I take the car out - it immediately heats up to 215 - then jumps back to 160 - right where I expect it to be. Runs at that temp for 20 miles of canyon carving. (It has pulled this trick several times)

2 days ago I take the car out - run it 40 miles - no cooling issue runs 165 - 170 the whole way - but it is an easy drive downhill - and cool in the morning. Run it back up the hill - hotter day - another 40 miles - temp slowly climbs to almost 200 degrees (I have a 160 thermostat).
Last night I take the car out -it runs up to 215 - back immediately to 160 - and stays there for 20 miles of canyon carving - agressive driving.

This morning I go out , the cars overflow tank is full of coolant and the radiator is full to - of course it is parked nose down on an incline. - I start driving - temp climbs to 260 within 8 miles.

I pulled out the thermostat (6 months old Stainless unit) , boiled it - it opened wide at 160.

Additional info :
Radiator : recored/rebuilt less than 1 year ago
AC Condensor - gone - it is pulled out - straight shot for air into the radiator.
No sign of water in the oil
Cooling Sysytem pressure tested - checks out OK
Fan - turning - the correct direction - and continually operating

So my only guess is intermittant failure of the thermostat - I am at a loss? any help here?

Carl "getting frustrated" Johansson

 

I'd start with the easy stuff. I would be highly suspicious of that thermostat or intermittent fan operation. Could also be an electrical issue ( ie loose wire, bad connector, partial short or open). The cooling system (engine wise)is in my opinion too mechanical to work one time then not the next- on a regular basis- other than a thermostat or radiator cap problem.

 

.....i vote for a sticking t-stat....replace it or get a "failsafe" t-stat which, if it fails, fails in the "open" position...

 

Tstat or a headgasket on its way out.

 

....geez, i forgot about the headgasket!......

 

Two things push coolant into the overflow bottle, stuck closed thermostat, leaky head gasket.

 

Did that new t-stat work???

 

Just has a similar problem on my 96 LT1. Turned out to be an intermittently sticking stat. New Fail-Safe stat solved the problem.

About $20 at AutoZone.

Jake

 

Nope! didn't fit. I love the idea - i just have to find one that fits!

So here where it ended up - I tried to put in a failsafe Thermostat Jr. Rifle coach had laying around. unfortunately the stem was to tall - it hit againsts the engine block and would not seat in the fitting inside the housing (the part of the failsafe unit that goes into the block is almost 2X as long - I guess it has to do with the mechanism. that made it so I was afraid that the housing would not fit flush.

By now it was 6 pm - so the nearest open parts store is now an 80 mile round trip away!

I scavenged a used 180 degree themostat from a Big Block I had sitting around drilled 2 1/8 inch relief holes - installed it and buttoned it up!

This morning - 90 miles to the autoX site 65 - 70 degrees outside - car runs at 177 the whole way (OD - 2000 rpm - 74 mph).

I run 5 - 1 minute AutoX's - temps rise to about 186 or s0 and then cool to 182 as I wait for my next run.

Then it's 90 miles home in 95 degree heat - car runs at 182 - to 184 degrees - I can cool it to 179 if I go to 1800 rpm and feather it a bit.

Obviously - it must have been a sticky themostat!

Thankfully - I really didn't want to think Head gasket - I like to drive the car - not work on it!

Carl "taught a few BMW's a thing or 2 today - but had my *** handed to me by WRX si. " Johansson

 

Hey Ron,
were you the guy talking about coming to Bopnneville in September - some forum member was wanting to come and participate - but i lost the Pm in a purge of the system - so I can't remeber who it was!

Carl 'this Alzheimmers aint for -.. uh whos was that? Joahnsson

 

......

 

I put a MotoRad FAIL-SAFE Thermostat, part # 7307-180 in my 96 LT1. Got it from AutoZone. About $20

Jake

 

Yes, that was me. Its been awhile.

 

So you coming - or are ya yella?

Carl Johansson

 

Italian disease-Fundsalow

If things pick up Id love to go.

 

Ill just say this. I had the EXACT same issues you were having for a LONG while. I couldn't pinpoint the problem. It did just what yours is doing.. ran fine one day, then the next day it would be fine, then just randomly jump to 240-250, then within a 20 sec time frame, jump back to 170 again as if nothing happened...even while moving. It was very sporadic.

I took a LOT of suggestions on here... and end the end the engine just had enough and blew another head gasket from one final overheat one day in the most inconvenient place possible.

SO... while I was replacing the head gasket, i went ahead and replaced the water pump, "just because" it was the only thing I hadn't replaced yet.

And there I saw it.. just BARELY visible ONLY after I had removed it.. the weep hole was leaking. The pump was bad and there was no way to tell other than after I took it out.

I replaced it and have not had a SINGLE issues since then.

Just some food for thought.