Pontiac GTO Forum banner
1 - 20 of 48 Posts

·
Registered
1968 Solar red GTO
Joined
·
29 Posts
Discussion Starter · #1 ·
Just Installed the 461 and letting her break in for al least 300 miles.

I installed a cool fit 2 row large core radiator (1.5’ cores) and a new clutch and fan (7 blade)

Having some odd heat issues- it has a 180 tstat, and runs 180 while driving easy. But when idling and slow driving it runs up to 210. It takes a while to get there (usually hovers around 200/205 when slow moving) the second it get going it goes right down to 180ish. This read on a mechanical gauge with the tap in the intake manifold

What do you guys think it is.

The fan sticks out a bit from the shroud (1’), and I’m using a OPGI sourced thermal clutch fan

When driving, there is zero issue, it just seems to heat up when idling in parking lots or sitting, its drops to 180 in 30 seconds once you get going..

Thoughts?
 

·
Registered
1967 400/400
Joined
·
1,889 Posts
Just Installed the 461 and letting her break in for al least 300 miles.

I installed a cool fit 2 row large core radiator (1.5’ cores) and a new clutch and fan (7 blade)

Having some odd heat issues- it has a 180 tstat, and runs 180 while driving easy. But when idling and slow driving it runs up to 210. It takes a while to get there (usually hovers around 200/205 when slow moving) the second it get going it goes right down to 180ish. This read on a mechanical gauge with the tap in the intake manifold

What do you guys think it is.

The fan sticks out a bit from the shroud (1’), and I’m using a OPGI sourced thermal clutch fan

When driving, there is zero issue, it just seems to heat up when idling in parking lots or sitting, its drops to 180 in 30 seconds once you get going..

Thoughts?
A 180 thermostat will NOT keep the engine running at 180. It merely opens at 180 (I assume you knew that). So expect to see it rise into the 200 range at slow cruising and stops.

I would also expect a new motor to run on the hotter side.

FYI, personally, Id never have a Pontiac engine without running a Flowcooler water pump and a drilled thermostat... Simply because I live in a hot state with a ton of tourist traffic. Water pumps arent created equal, so if yours has a stamped impeller, they are very poor in the efficiency dept.
 

·
Registered
Joined
·
23 Posts
What size waterpump pulley are you using? My 66 had the same temp creeping issue at idle, even with the MK-VIII fan, so I knew it wasn't an airflow problem. Once I switched to a smaller 6-1/2" AC pulley the average idle and low speed temp dropped by about 10 degrees.
 

·
Registered
Joined
·
545 Posts
A 180 thermostat will NOT keep the engine running at 180. It merely opens at 180 (I assume you knew that). So expect to see it rise into the 200 range at slow cruising and stops.

I would also expect a new motor to run on the hotter side.

FYI, personally, Id never have a Pontiac engine without running a Flowcooler water pump and a drilled thermostat... Simply because I live in a hot state with a ton of tourist traffic. Water pumps arent created equal, so if yours has a stamped impeller, they are very poor in the efficiency dept.
^^^ X2 on the Flow Cooler water pump.

Like Army said 180degree thermostat is where it opens to BEGIN cooling. If you had a 160 thermostat it would start at 160 cooling and probably level off by 180.

If its an iron headed motor it will naturally run hotter than an aluminum headed motor.

Also, “Hot” is a subjective term. LS motors dont even turn on fan #1 until 210-215 degrees. If you get up to 200-205 and it never gets any hotter than you have no issues. Its definitely understandable to want it to run at 180. I always do. But you’re not “over heating” until you bubble fluid out of the radiator which usually happens around 245 degrees depending on your radiator cap PSI rating. Also running the motor at 200 will net more life out of a motor than running at 180. Again i love seeing my cars run at a stable 180. But if yours is a stable 200-205 in traffic and never gets any higher than the cooling system is doing its job.

For people that want to see it as low as possible in a hot climate, we will take the guts out of the thermostat and just leave the outer portion. This will allow the radiator to start cooling immediately. The cold climate guys cant do this because the motor will never heat up. Here in florida 11 months out of the year its 95-100 degrees with 100,000,000% humidity. The engine is going to heat up in a few minutes regardless of thermostat.

You also have the option of going electric fans which can move more air at idle (if you get the correct ones). But that also requires an alternator upgrade most of the time.

A small helper is Water Wetter. It can lower temps 5 to 10 degrees sometimes. For 10 bucks its worth dumping a bottle in.
 
  • Like
Reactions: armyadarkness

·
Registered
1967 Lemans 1967 GTO parts car
Joined
·
540 Posts
^^^ X2 on the Flow Cooler water pump.
For people that want to see it as low as possible in a hot climate, we will take the guts out of the thermostat and just leave the outer portion. This will allow the radiator to start cooling immediately. The cold climate guys cant do this because the motor will never heat up. Here in florida 11 months out of the year its 95-100 degrees with 100,000,000% humidity. The engine is going to heat up in a few minutes regardless of thermostat.
Moved to FLA in the 1970s. Both cars my family brought from up north did not make it a month before puking thier guts out in a parking lot.(no puke tank). We moved just off the main drag to the islands and would watch to see how many northern cars could not putt the 8 miles to the beach. It was a common thing even when cars were not that old.
 

·
Premium Member
Joined
·
1,904 Posts
Keep in mind that the original factory installed thermostat for a 68 was 192* and the engine would normally run at 200*. If you had warning lights, the sensor was set to 230* before the overheating light would come on.
I agree with Army that the engine is still tight and will run a little warm until fully broken in and that a good water pump is essential at lower engine speeds. But there's nothing wrong with the factory pump as long as it has the cast iron impeller and the impeller is spaced correctly to the divider plate.

Ideally the fan should be half in, half out of the shroud. If its sitting out of the shroud you're not pulling all the air through the radiator that you should be. This may be a problem at lower vehicle speeds.
Do you have the 11 bolt water pump or the original 8? Different lengths for the 11 bolt which may be why your fan isn't where it should be.
What brand name and part number is the OPGI clutch fan? There are different temperatures that they will engage at.
 

·
Registered
1968 Solar red GTO
Joined
·
29 Posts
Discussion Starter · #9 ·
Wow

This is great info!

It’s a new water pump, but I don’t know the impeller type (i am inquiring) I have to assume that its the cast variety)

I have the 8 bolt pump- and the fan blades are 1/2 way into the shroud (I didn’t know if they should be fully in the shroud) so i was thinking spacer.

I am wondering if i need a smaller pulley to turn the water pump faster, or switch it to a 160 tstat.

It sat idling yesterday for 10 mins are rose to 215/220, the second you drive off, it cools down fast, like 30 secs or so.

I’m using the stock pulleys i had off the old 400, what size is available to use to turn the pump faster?
 

·
Registered
1967 400/400
Joined
·
1,889 Posts
Wow

This is great info!

It’s a new water pump, but I don’t know the impeller type (i am inquiring) I have to assume that its the cast variety)

I have the 8 bolt pump- and the fan blades are 1/2 way into the shroud (I didn’t know if they should be fully in the shroud) so i was thinking spacer.

I am wondering if i need a smaller pulley to turn the water pump faster, or switch it to a 160 tstat.

It sat idling yesterday for 10 mins are rose to 215/220, the second you drive off, it cools down fast, like 30 secs or so.

I’m using the stock pulleys i had off the old 400, what size is available to use to turn the pump faster?
If you have a Pontiac 461 idling for 10 minutes at 215, in California, then your problem is slight, with room for improvement. Above all else, you need to view the cooling system as a complete system and design it accordingly. Focusing on individual parts is going to send you down the rabbit hole.

Also... dont know your engine builder, but I never saw one care about cooling... so don't assume that they built your engine to cool at maximum efficiency.

  • If you read our previous posts, you'll understand that dropping the thermostat "opening" temp will not help. Your car runs a 215 degrees, whether the tstat opens at 160 or 180... so again to clarify, the tstat temp is NOT what you run at, it's what you open at. Or if you prefer, your car will now start running at 215, sooner with a 160. But drilling bypass holes in the tstat WILL help.
  • A smaller pulley WILL help, BUT ONLY if you need it. So if you have the OEM pulley and everything else is right, then you have a problem somewhere else. A smaller pulley can be a great modification for a purpose built cooling system, but throwing a smaller pulley on to mask a crappy water pump is a waste of time. Yes, it may drop temps 20 degrees, but getting a better pump will likely drop it 20-30 degrees, too. Dont consider a pulley swap until you verify the water pump.
  • If your water pump came from autozone, amazon, etc, assume that its not great. For your 8 bolt pump, the Flowcooler with the blue impeller is the best available. And... you're not just getting better flow, youre also getting better bearings.
As I said, view the system as a whole. Putting a great radiator on a system without clearanced plates and the right impeller, is like putting an 850 double pumper on a straight six with a cork in the tailpipe.
 

·
Registered
Joined
·
1,974 Posts
Sounds like an air flow problem at idle like the gang said, I would use a 160 testator, and make sure that you fan shouting is really well sealed around it. There was factory rubber baffles Ames sells them that seals that off. Also make sure that you wheel well flaps are in place, they actually help with the way air flows in there overall. But they effect it more at speed than idle.

agree to check the clutch fan temp, when it comes on, they do wear out and the viscous fluid inside gets old, so you may need a new fan clutch or different one. A small increase in idle RPM will help also. Itmakes the fan turn faster and water flow more.

if the cam is not stock and the engine is not stock trying to run at some factory idle setting of 500 or 600 Rpm’s can contribute to idle heating. Modified cams and engines idle higher 750 800 is ok and may run cooler.

Also retarded idle timing adds to engine heat. If you have some low idle timing like 4 or 6 BTDC that can contribute to hot idle. Best to run it at idle between 20 and 30 BTDC with 10 degrees of that coming from vac advance.

Agree with the gang, flow kooler. And 11 bolt pump is better, but yours can work.
 

·
Registered
Joined
·
1,974 Posts
The cooling system has to work Harder to cool something down, than it does to not let something heat up. Just like an air conditioner. Say your room is 70 degrees and you want 60 it does not have to work that hard to get there. But from 100 degrees to 60 it has to remove a lot of heat to get there.

so you would be better off to start cooling that room off with the thermostat set to 60, than leaving the AC off and letting it get to 100 and trying to cool it down.

Now army is right, as he often is that if your cooling system won’t cool good what temp the thermosat opens may not matter. However if your system is set up right, when it opens at 160 the engine starts cooling and it can more efficiently keep it cooler than when it opens at 180 and it now has that added 20 degrees to try to cool down, that is harder, and the temp climbs easier.
 

·
Registered
Joined
·
23 Posts
I am wondering if i need a smaller pulley to turn the water pump faster, or switch it to a 160 tstat.

It sat idling yesterday for 10 mins are rose to 215/220, the second you drive off, it cools down fast, like 30 secs or so.

I’m using the stock pulleys i had off the old 400, what size is available to use to turn the pump faster?

The 6-1/2" pulleys came on AC cars and I believe the non AC pulleys were 8". AMES lists both. You can never have too much flow through the radiator so even with the best pump I'd still use the small pulley.
 

·
Registered
Joined
·
5,827 Posts
Option #1 -You have an air flow issue or the radiator is too small - cools down once you are moving which forces more air through the radiator.

Option #2 - You have not optimized/dialed in your timing events. Assume vacuum advance?

Option #3 - Carb running a but lean, but would not look at that until Option #2 have been verified.

Option #4 - All of the above.
 

·
Registered
1968 Solar red GTO
Joined
·
29 Posts
Discussion Starter · #15 ·
The 6-1/2" pulleys came on AC cars and I believe the non AC pulleys were 8". AMES lists both. You can never have too much flow through the radiator so even with the best pump I'd still use the small pulley.

So my car is a factory ac car, ill measure the pulley later for sure………I’m sure i have that pulley then
 

·
Registered
1968 Solar red GTO
Joined
·
29 Posts
Discussion Starter · #16 ·
Option #1 -You have an air flow issue or the radiator is too small - cools down once you are moving which forces more air through the radiator.

Option #2 - You have not optimized/dialed in your timing events. Assume vacuum advance?

Option #3 - Carb running a but lean, but would not look at that until Option #2 have been verified.

Option #4 - All of the above.

Greta input- i actually think the carb is running really fat- i went through a tank in less than 100 miles, driving it in “break in” condition- its a bit hard starting too, takes about 10 cranks

I need to recheck timing

Radiator is a cool case they said would cool 800hp, 2 core aluminum with 1.5’ cores…

I think the fan (6 blade factory non flex) and thermal clutch is the culprit, it may not be drawing enough through.
 

·
Registered
Joined
·
5,827 Posts
It’s looks like its not far enough into the shroud



View attachment 147641

A new engine can run a little hotter because it has to "loosen up" a bit, but not much hotter.

What oil weight? Oil is also a means to cool and engine. Thicker oil may not transfer heat as well as lighter oil. Just a thought.

Yes, you want 1/2 in and 1/2 out as the typical positioning.

Radiator should do the job at the specs you have.

Get a hand held laser temp gun and shoot the radiator at the top and the bottom to confirm radiator temps and there should be a noticable difference. This will also verify your gauge and can save a lot of head scratching and time if it is a gauge/sending unit issue/mismatch.

Your belts could be slipping and not know it. I have had that experience. The pulleys have a specific V angle and some of the replacement belts are close, but no cigar. They can be too skinny and not grip well, or even drop too deep and ride on the pulley center rather than the sides of the pulley. The belts that seem to be correct are the Dayco brand Top-Cogged belts.


Other things are the amount of slip from the clutch fan unit. The HD units will slip less at lower RPM's, but drag more into the upper RPM's - so pro's and con's for the real HD units. Hayden is the brand that most seem to use and I myself have used them with no issues.

The fan blades can be made at different pitches, More of a pitch/angle will cut more air at the lower RPM's.

Again, get the timing dialed in to eliminate that.

Definitely using way too much gas, in my opinion. Not good because you could be "washing down" the cylinder walls of oil and not good when breaking in a fresh engine. If you had a real healthy engine, or 3.90 gearing, I can see 10MPG's. I think you should be doing a little better.

So get that squared away as well.

(y)
 

·
Registered
Joined
·
1,974 Posts
Agree with solar not in the shroud at all. You could put on an 11 bolt water pump and timing cover and extend it or get another shroud and put it in. That will not cool at idle worth a dang,..you need to fix that first

you could get a different shroud from Ames and Hayden sells fan clutches with a 3 inch shaft and a low profile shaft so you could adjust. Shrouds can be cut or custom made as well.
 
1 - 20 of 48 Posts
Top