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gtochism · 05-08-2003, 09:52 AM

My son has a 68 gto with a 69 400 engine, with 400 6x heads , o68 cam, stock new exhaust,[21/4 with turbo's] new cast water pump, new plate behind the water pump. new 3 core radiator [none ac car].160 thermostat 15 lb new radiator cap, new heavy duty thermostatic clutch fan ass. with a gto 6 blade fan hooked to it. timing is 36 deg. total. Vacume advance is hooked up.it has a turbo 400 with stock 325 gears.the fan shroud is in place and filler panel added[covers nose to rad support opening.]car runs 180 in town,240- 260 or more at 70 mph at 80 degreesoutside temp.The r- bank is pulling oil.Could this cause the temp. problem?The guy that did the heads didn't do the guides right on that one on the right side. the time span between instilation and return has expired before i knew of the problem. it has transmission cooler mounted ahead of the radiator [4 to 6 in. clearance ahead of the radiator.Any body got any ideas? thanks Frank

gtochism · 05-08-2003, 09:52 AM

My son has a 68 gto with a 69 400 engine, with 400 6x heads , o68 cam, stock new exhaust,[21/4 with turbo's] new cast water pump, new plate behind the water pump. new 3 core radiator [none ac car].160 thermostat 15 lb new radiator cap, new heavy duty thermostatic clutch fan ass. with a gto 6 blade fan hooked to it. timing is 36 deg. total. Vacume advance is hooked up.it has a turbo 400 with stock 325 gears.the fan shroud is in place and filler panel added[covers nose to rad support opening.]car runs 180 in town,240- 260 or more at 70 mph at 80 degreesoutside temp.The r- bank is pulling oil.Could this cause the temp. problem?The guy that did the heads didn't do the guides right on that one on the right side. the time span between instilation and return has expired before i knew of the problem. it has transmission cooler mounted ahead of the radiator [4 to 6 in. clearance ahead of the radiator.Any body got any ideas? thanks Frank

David Jones · 05-08-2003, 10:11 AM

Hear is a link to some overheating problems. See if any of these fit.
Good luck.

http://kurtspontiac.homestead.com/DavidJones69GTO.html

gtochism · 05-08-2003, 07:09 PM

THANKS DAVID, I WENT TO THE WEB SIGHT BUT FOUND NOTHING.I'VE RUN OUT OF IDEARS.

goathead68 · 05-08-2003, 07:22 PM

It sounds like it isn't getting all the advance it needs at highway speeds. I had a problem with my distributor three years ago. The advance mechanism was binding up in the distributor. I disassembled the distributor, cleaned everything up and relubed where necessary and reinstalled the distributor. It works fine now. The car ran upwards of 230 on the highway when the distributor messed up; it now runs 200 at 70 mph in 80 degree weather.

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gtochism · 05-08-2003, 08:57 PM

THE DIST SHOULD BE OK IT'S A NEW DIST. WITH THE TOTAL SET 10 AT THE CRANK WITH 36 DEG.TOTAL ALL IN BY 2000RPM.

David Jones · 05-09-2003, 06:19 AM

Ever run a hotter thermostat? 180/195. Really sounds like the radiator capacity is not big enough. If all the other items are in good working order and your sure the distributor advance is operating correctly then you really need to look at capacity.

http://kurtspontiac.homestead.com/DavidJones69GTO.html

Txbobcat · 05-09-2003, 06:59 AM

Does it really seem to be getting hot. Just wondering about the gauge? You could install a cheap aftermarket for a day or two and compare the readings. Other than that put the old fan clutch on and try it again.

mike nixon · 05-09-2003, 07:17 AM

verify that the gage is reading correctly.

make sure all of the belts are tight and not slipping.

what kind of compression does the engine have?

have you tried richening up the fuel mixture?

mike

gtochism · 05-09-2003, 03:19 PM

FIRST THANKS EVERYONE FOR THE FEED BACK.TO ANSWERYOUR QUESTIONS.I CHECKED THE DIST ADVANCE MYSELF. IT LOOKS FINE, I TRIED A 180-195 THERMOSTAT, IT GOT HOTTER. I M LEANING TOWARD A BIGGER RADIATOR, OR PULLONG THE PUMP TO CHECK THE IMPELLA. BELTS ARE TIGHT CHANGED THERMOSTAT AT LEAST 3 TIMES NO DIFFERENCE.I HAVE A COUPLE OF EXTRA TEMP GUAGES. I WILL TRY A DIFFERENT GUAGE BUT THE ONE ON THERE READS 160 UNTIL YOU HIT THE INTERSTATE. IT RAN THE SAME TEMP WITH THE OLD CLUTCH FAN AS THE HEAVY DUTY ONE.I HAVE NOT RUN A COMPRESSION TEST. THAT,S NEXT. IT IS RUNNING A QUADRAJET [700-750?] OFF A 455.RUNS 15 INCHES VACUME AT IDLE.[STEADY READING] I COULD RICHEN THE FURL MIXTURE. BUT WOULDN'T THAT COOL DOWN THE CYL. WALLS WITH THE EXTRA RAW FUEL? THANKS FRANK

mike nixon · 05-09-2003, 09:53 PM

i'll bet the carb isn't flowing enough fuel for the combo that you have..

a good clean stock 3- 4 core radiator should cool what your running.

mike

gtochism · 05-09-2003, 10:50 PM

WELL I DON'T KNOW MIKE. LIKE I SAID THE CARB IS AT LEAST A 700 OR 750 QUADRIJET. IT'S BASICALLY A STOCK GTO. THEY CAME WITH A 650 CFM CARBS. AND THE RADIATOR IS A NEW 3 CORE. I KNOW THE STOCK GTO'S CAME WITH A 4 CORE. BUT I HAVE A 75 T/A WITH AC OUTSIDE RUNNING A 2 CORE THAT ISN'T OVERHEATING.I KNOW THE TWO INSERTS ARE IN BEHIND THE PLATE IN THE NEW WATER PUMP BECOUSE I PUT THEM THERE. I'M AT A LOSS WITH THIS ONE. I'M THINKING OF COMPLETELY REMOVING THE THERMOSTAT AND SEE WHAT HAPPENS.

ichabod · 05-10-2003, 11:36 AM

I Know this may sound simple, but I had the same problem with my 65 GTO 389. New 3 core rad. new cast impeller pump, shroud, 6 blade fan. The GTO still ran 215-220. Replaced coolant 50/50 mix with 1 can of 40 Below and water, left remaining coolant in block justed drained rad. Went from the above temps to 180-185 on highway and around town. This is with 4:33 gears, so Iam turning some rpms on highway. Good Luck.

merlin · 05-10-2003, 02:35 PM

Frank, I had a overheat problem on the same engine. I have it in my 64 Lemans. here's what I did- #1 added an electric fan in front of the radiator,#2-had a new radiator built with 5 rows of 3/8 tubes,#3 moved the trans cooler out from in front of the radiator, off to the side,#4 wrapped the trans cooling lines to protect them from the headers,#5 new STOCK shroud,#6 largest fan that would fit inside the shroud,#7 160 thermostat. I now run at 160, if I get in traffic-200 topps. Good luck. Merlin

goathead68 · 05-11-2003, 10:26 AM

A few questions:

1) Is the car spewing any coolant out of the overflow after you run it on the highway?

2) Does the temp drop fairly quickly after you get off the highway?

3) What's the water level in the radiator when the engine is cold?

4) Has the cooling system been flushed recently? Sometimes an accumulation of rust and/or scale in the cooling passages of the engine will cause the engine to overheat, even if everything else is new or normal.

5) Did you check the vacuum advance unit, too? A correctly operating vacuum advance canister will give you another 10 degrees or so advance at highway speeds.

6) What kind of gauges are you using, electric or mechanical? If you're using electric, sometimes the sending unit will screw up.

7) Do you have good vacuum at the manifold? If the vacuum seems a little low, you may have a vacuum leak somewhere, which may cause an overheating situation, too.

The fan clutch really shouldn't make a difference at highway speed. It will help around town, though, as it helps to pull more air through the radiator when vehicle speeds are low.

Like Mike said, a lean set-up carb will cause the engine to run warm. A little rich on the mixture is a good thing.

The car should run about 160-165 in town with that thermostat. I have a 180 in mine and it doesn't get much above 180 in town, 195-200 on the open highway. I have a stock replacement four core radiator, stock water pump and plates, stock 7 blade fan with a heavy duty fan clutch, fan shroud, stock trans cooler, functional A/C, Auto Meter mechanical gauges, timing set at 12 BTDC, 34 total, all in by 3000 rpm, 3.23 rear gear. It turns about 2800 rpm @ 65 mph on the open road.

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[This message was edited by goathead68 on May 11, 2003 at 01:47 PM.]

gtochism · 05-11-2003, 08:09 PM

THANKS PY68 FOR YOUR AND ALL OTHER INPUT.TO ANSWER YOUR QUESTIONS. [1] YES IT SPEWS COOLENT OUT BUT ONLY AFTER SHUT OFF. WE NOW HAVE A CATCH CAN FOR THAT.[2]NO THE TEMP TAKES A WHILE TO COME DOWN AFTER GETTING OFF THE INTERSTATE, HAVE TO DRIVE AROUND AWHILE. [3]WATER LEVEL AT MARK ON RAD. SIDE, ABOUT 3-4 INCHES BELOW FILLER NECK.[4]BLOCK PRESSURE WASHED WITH FREEZE PLUGS OUT BEFORE ASSEMBLY.LESS THAN 4000 MILES ON ENGINE. [5] VACUME ADVANCE NEW WITH NEW DIST. ADVANCE CHECKED BOTH UNPLUGGED AND CONNECTED.LOOKS GOOD.[6] USING A MECHANICAL A TEMP. GUAGE.IT ENTERS THE ENGINE BAY UNDER THE HEATER BOX R-SIDE BY HEADER. IT,S ABOUT 6 INCHES FROM HEADER. COULD IT BE PICKING UP THE HEADER TEMP. BECOUSE OF ITS LOCATION? IT THEN CONTINUES UP THE BACK OF THE ENGINE ACROSS THE VALVE COVER TO THE FRONT OF THE INTAKE AND CONNECTS BY THERMOSTAT HOUSING. [7]HAVE GOOD VACUME 15 INCHES STEADY. I SPRAYED INTAKE AND CARB TO SEE IF ENGINE RPM CHANGED. IT DIDN'T. I AGREE ABOUT THE FAN CLUTCH. AT HIGHWAY SPEED YOU OUGHT TO BE ABLE TO THROW THE FAN AWAY AND IT STILL COOL.I HAVE A EDELBROCK CARB I COULD TRY. AND ANOTHER MECHANICAL GUAGE. FRANL

meanolegoat · 05-12-2003, 04:41 PM

Mine was doing the same thing when I bought it. Did very little driving b-4 tearing down. When changing the cam/heads I found that somebody had left the inserts out of the timing cover...just a thought...
"mean"

goathead68 · 05-24-2003, 06:59 PM

Frank,

Everything sounds like it's normal, except for the temp. Did you try to richen the fuel mixture a bit? An easier thing to do would be to check the cap. It may not be holding pressure, even though it's new. Stranger things have happened.

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Sun Tuned · 05-24-2003, 07:26 PM

Let me ask a couple of questions.... With the vac adv hose disconnected, what is the initial timing set at, at idle. In terms of crank degrees? At what crank rpm does the centrifugal advance begin. In other words, at what rpm does it read when any advance over what your initial is set at begins?

trshman · 05-24-2003, 08:41 PM

50tooslow,
I've got a '70/400 block w/6x heads and I'm running approx 14 deg adv at idle thanks to suggestions I got at PY so I'd suggest trying that. Also check pulley diameters, Pontiac had a tendency to underdrive pumps. I've got 8" crank & 6 1/2" water pump. I run approx 200-205 at 85-90 outside temps at approx 70-75. I've got approx same setup except for 4 core Harrison. In town driving like a tourist I'll run 165 or so, both figures w/no AC.
Hope this helps. Good luck.

Bob G.
Hollywood, FL

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