[topless lemans]

Have a mild built 455 with 6x heads, 4 core aluminum rad, newer clutch fan. Runs around 190 and when I did a cruise with slowww traffic got to 200~205 but as soon as I got going it went back down.
I can cruise along and pull into McDonalds for a sweet tea and im in line and waiting since there SLOOOOWWWWW last time it jump to 210 but as soon as I leave goes back down. Does ok 95% of the time.
This normal or not? Someone told me I can add a pusher fan on for this case when I need it and turn it one

[mscicluna007]

We had the same problem with a 400 Pontiac after a rebuild to 60 though oversize with Edelbrock heads.

It was only at idle or when car was stuck in traffic where the temperature climbed and would not come down until you started drive.

The cause turned out to be a few simple tops which did not amount to alot of money.

Looking back at what changed after a rebuild the first noticable thing was the water pump, backing plate and timing cover.

Radiator is still the original 4 core which is fine.

So looking at the pump and backing plate over the years the manufacturers of the parts have changed as has the metal used and the tolerances on the parts.

The backing plate should clear the impeller blades by 0.060 inch clearances but quite often is far more.

Their is two solutions. No. 1 is to remove the water pump and backing plate and using a press or something large enoiugh to fit over the whole and hit the backing plate to close the distance to the pump by reworking the centre towards the blades until the desired clearance keeping in mind gasket clearance also.

This is shown in Jaim Hands Book - How To Build Max Performance V-8s on page 143.

The second option is what we used which rather than to decrease the capacity the pump could run at but increase it by increasing the blade diameter. Small stainless strips were welded to each blade to increase impeller size which worked really well.

No more cooling issues at idle. The cause is aeration of the coolant between the backing plate and the pump and the heat builds slowly . Increase the pumps efficiency and you can cure the problem.


A 7 blade GTO clutch fan works a treat also if you are still having issues. Make sure you have a cowl as that helps to create a vaccuum from the radiator to the van which draws all the air out of the radiator to allow it to cool efficiently.

Last if all this fails you can remove your thermpostat and drill a small relief hole much the same as the hole withthe little pin in their as a relief hole to allow some water to flow constantly whilst the thermostat is closed but i don't think you will need this option after the water pump mod.

Here is some pics of our water pump mod. and you can see the small dots of braising and the actual height of the strips that the pump has been increased by.

I think Edelbrock and a few other companies make high flow water pumps for better efficiency at idle but this worked best for us.

Good Luck

Michael

[topless lemans]

Forgot to add, I do have a high flow water pump, got it from one of the suppliers. Might add the hole but isn't that just for warming up only?

[mscicluna007]

It helps by allowing water to flow constantly at a controlled rate rather than taking the thermostat out completely. It would probably be one of the last mods i would be doing.

I would still concentrate on the backing plate clearance to the water pump first as your problem is at low revs soyour pump may not be efficient enough.

Another thing you can check is your pulley size as you may need to go to a smaller pulley to turn the pump faster . I can't remember exact sizes so i won't put you on a bum steer but their would be countless threads in the past on these same issues.

Your cowl is also important as it creates a vaccuum of air from the radiator and throws it past the engine. A large fan that sits in the cowl perfectly without touching is ideal Like the GTO Fans. i think off memory they are 19 1/2 inches 7 blade fan .

We initially had the thermo fan also , FlowCooler Water Pump. and flexilite Fan initially
and this was all under the nose of a 79 T/A which doesn't move much air aound.

Now a stock water pump with mods, GTO Fan with clutch and never looked back.
Since all these mods we have taken the thermos out and been out in 40 degree celcius summer days in traffic with no overheating issues anymore or any concern of climbing temperatures.


Not to say aftermarket parts don't work but look at the history of these engines and whats changed over the years because these were all around the place in the old days without half of the issues and just as much engine work.

[topless lemans]

I do have to do some more digging, looked at the Jim Hands book and he was running a 160 stat which I find interesting since a lot people say to run a 180 stat. I forgot about the pully size. I do have a after market cowl but would like to find a nos part, see if there is a difference

[rexs73gto]

Are you talking about a shroud , not a cowl, as the cowl is behind the engine & above the firewall, also a part of the firewall just the top part. Without a fan shroud you will have the conditions you are talking about. Also with the fan it needs to be at the entrance of the shroud or slightly inside the shroud so the air doesn't go around the fan but the fan pulls the air past the fan inside the shroud so the air has to be pulled directly through the raditor.

[topless lemans]

That's what I thought he meant to, yes I have a shroud and fan sticking half way out

[mscicluna007]

I am sorry i do referance it as a cowl and yes i meant a shroud.

And i said it more than once. LoL.

Sorry my mistake.

[mscicluna007]

http://forums.maxperformanceinc.com/...d.php?t=411256 worth the read also

[topless lemans]

Was reading that, looks like I might trying a new water pump

[mscicluna007]

If you do end up going that way before you put the new one in check the clearance on your old pump with the backing plate as if the clearance is large closing that distance maybe enough to solve your problem. Good Luck

[sts]

Do you know why Jim uses a 160' and Pontiac uses, actually, it's a 190'?

Hint: Both are performance thermostats. The difference is what performance people are seeking. Another tip: It's in the book, right there in print Pontiac uses a 190' thermostat for . . . .

The specks aren't in the book because it isn't conidered as a servicable car. But I remember seeing ra with heater delete with a factory 160' thermostat.

I'm not going to waste my breath telling you it's normal because you have a whole crew here who is waiting to tear your car apart, starting out by snapping off the mounting bolts on your timing cover.