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Overheating Concerns '67 Bird 400

8K views 66 replies 16 participants last post by  Skunk Works 
#1 · (Edited)
I'm still working on this '67 Firebird that belongs to a local guy. I have completed some suspension upgrades and installed the interior and am now tackling the drivetrain concerns.

I took it for a 1.5 mile drive, after idling for a few minutes, and the temp went to 207 degrees before I shut it down. He had said he hasn't been driving it because it quickly runs up to 210 degrees. A few minutes after I shut it down I used the laser thermometer that read 187 at the intake manifold beside the thermometer sending unit. I expected it to read higher than that.

To help I installed a set of the factory design closeout panels between the radiator bracket and the nose of the car. I had installed a thinner fan spacer to pull the fan out of the shroud but then the fan blades hit the power steering pump. :frown2: Presently it has a 2" spacer, my .5" spacer placed the fan blades about 1/3 into the shroud but as said the blades hit the steering pump. I have already boiled the thermostat on the stovetop to determine it fully opened at 180 degrees. I'm confident it is okay. It has a BeCool aluminum radiator that should be very sufficient.

One thing I noted is this engine has a bad dieseling problem when shut down. Also, for the short drive, I noted hesitation when accelerating. This engine was built by a local guy but he hasn't been able to give me any specifics.

So, might the root cause of all this be timing? Should I shoot for 36 degrees BTDC? I know I also need to check centrifugal advance and vacuum advance. I believe presently it has 87 octane gasoline and just about empty. I will refill with some 93 octane non-ethanol.

I figured I would check timing in the morning before the heat of the day. Right now outside it is 90 degrees with enough humidity to make it uncomfortable. So, I'm taking a break from it.
 

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#5 ·
I would start by ditching the flex fan and installing a stock type 5 blade. The dieseling can be caused by Timing advanced to far, that also adds to increased temps. This can also cause the hesitation you described. I would 1) replace the fan 2) review/adjust timing 3) check plugs to determine if its running lean (also cause a hesitation and high temps)
 
#7 · (Edited)
The fan is mounted correctly. The engine turns counter clockwise as viewed from the driver's seat. I too am suspect of the timing and the fan. I think first I'll check the plugs and set the timing. The optimal fan, even though it isn't correct for the car, will be the heavy duty 7 blade fan with the clutch like on my car. Two more blades should move 40% more air, that is providing each blade has the same capacity. Will a "stock" 5 blade be more efficient than this aluminum fan?

It's good to know the distributor turns the opposite direction.

I picked up some 93 octane no-ethanol for the next test.
 
#12 ·
Indeed it is. :smile2:

Check that there is no air trapped in the engine. Pontiac seems to be notorious for overheating at times because of this. I bought a 69 Judge from a guy in the 80's that couldn't figure out why it kept overheating. All it needed was to be burped so to speak. Just a thought.
So how does one burp a poncho engine? I cannot throw it over my shoulder.
 
#11 ·
Check that there is no air trapped in the engine. Pontiac seems to be notorious for overheating at times because of this. I bought a 69 Judge from a guy in the 80's that couldn't figure out why it kept overheating. All it needed was to be burped so to speak. Just a thought.
 
#14 ·
How accurate is the temp gauge? Is it electric or mechanical? Can you put the bulb in known temp hot what to determine if it is accurate?

Dieseling can be timing. Just move the distributor a bit and see if it goes away. Can be done easily enough without a light.....
 
#15 ·
This car has one of the fancy dash carrier inserts with digital everything readouts. The temp gives actual temperature and the sending unit is top front of the intake manifold. I removed plug #2 and pictured below. It looks really wet. But, this car probably only has a few miles since assembly due to the overheating concerns.

I checked the vacuum advance can and it is all in at 13. It was connected to port vacuum, I'll move it to manifold vacuum. I've yet to determine how much vacuum the engine produces. The distributor has a working centrifugal advance.

I might try Bob's idea of dropping the temp sending unit in a pot of hot water to see if it matches my thermometer.

I hope to get out there Saturday morning before it gets too hot and work with it. We were 93 degrees today and expect the same for the foreseeable future.
 

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#16 ·
I checked the vacuum advance can and it is all in at 13. It was connected to port vacuum, I'll move it to manifold vacuum. I've yet to determine how much vacuum the engine produces. The distributor has a working centrifugal advance.
I'm pretty sure you found the problem.

The initial timing is probably off too.
 
#17 ·
I have the timing set to 36 degrees with the vacuum can disconnected. I adjusted the air/fuel mixture screws and this engine tops out at 12" vacuum. I took it for a ride and observed the temp staying at 186 and 187 degrees. When idling it wants to go into the 190s. And the hesitation and dieseling I observed earlier seem to be gone.

I found the distributor clamp bolt was bottoming out before it secured the distributor. I cleaned out the block threads and shortened the bolt length. The vacuum advance is now connected to manifold vacuum.

I believe I should swap out the vacuum can to all in at around 10 or 11". This engine isn't making enough vacuum for this 13" can. Does anyone have a recommendation for a can?

What is the correct cooling fan for this engine combo. I noted it has a 21.5" diameter shroud so I would think some 20" fan. I don't believe they had the clutch fan in '67 but would be willing to use one.
 
#18 ·
Here's vacuum can specs. You'll have to cross reference the Echlin numbers. Many
of the numbers are discontinued. I ended up with a Delco D1310C (B26) from Rockauto
and made a limiter because it pulls in 16 crankshaft degrees. My understanding is 12
crankshaft degrees from the vac can is all that is needed. So attach a vacuum pump to
the can and with a timing light see how much vac it takes to pull in 12* with the can you
have. If it's less than 11" (2" less than available) you can just use a limiter on the can.
http://www.vetteclub.org/warehouse/tech/Ignition/distributor.pdf
 
#19 ·
It already has the Delco D1310C B26 vacuum can. Max open at 13", just like I had measured. Considering the difficulty of finding anything better it seems to be a good choice.

I've about exhausted all my easy options to improve cooling. The 180 thermostat functions correctly. The fan is almost totally into the shroud but it clears the power steering pump by .700", so not much room to adjust it out. I did order a 1" fan spacer to replace the 2" spacer but am now concerned the blades will hit with the 1" spacer.

It seems a 5 blade fan is correct, even though it is a flex fan. I'm hesitant to replace the fan while I don't have the room to properly place it into the shroud. I'm wondering if there is a 7 blade available.

My last drive it hovered at 186/187 while in motion but went into the mid 190s at idle.

Should I try a 160 degree thermostat? I wish there was a 170 degree thermostat option.
 
#20 ·
For a generic 400

Initial: 10/12 degrees
Mechanical advance: 22 degrees for a total of 32/34 degrees, spring to start 100 RPM's over out of gear idle RPM's

Now, for the tricky part, vacuum advance needs a degrees stop to limit the pull pin. best to either build a home made metal one, or, Crane 99619-1 plate, adjustable, works well.
Once completed, set the degrees stop to give 10 degrees, and connect it to full manifold vacuum only, not ported. This will give 20/22 degrees if IDLE timing after the engine starts and builds vacuum.

Ported vacuum actually is for emissions engines with functional EGR systems, adding a second acceleration advance curve non-emissions engines do not want, nor need. This increases combustion chamber temperatures to help burn more fuel to lower emissions levels. Ported vacuum advance also usually slows down mechanical advance to a level not workable in a non-emissions engine. If the engine runs better with ported vacuum advance, fix what is wrong with it, and the distributor curves.

Black plugs don't say a lot for the timing curves, engine might be so rich to try to compensate for the timing being way off.

I prefer stock large fans, with A/C fan clutches. On Pontiac, there are two diverters between the block and water pump, if they are not in place, cooling issues can occur.
 
#21 ·
Cars used to run all the time ok with no vacuum advance. The customer didn't know it was bad. Only during a tune up did it get checked, and replaced. Hell, they would think everything was fine with no vacuum advance and the centrifical all siezed up.
Timing set at 36, I assume that is initial and centrifical. For a higher compression engine, that is a bunch of timing, I'm told pontiacs do not need the advance that a chevy needs??. My firebird 400 needs 30 total or it will detonate with 91 octane.
Personally, I wouldn't sweat the vacuum advance being related to overheating. I normally run my cars ported vacuum. I have my 73 with 11.5:1 that likes manifold vacuum for advance and very little centrifical. I do believe using manifold vacuum may help, but I think very little if any.
I don't like flex fans, use electric or a big 19.5" clutch fan. You have to be moving air through the radiator, if it is with a fan, or driving down the road.
I have a Be Cool radiator and a 19.5" fan on my 68 firebird 400 and it runs cool. Even when it is 115 deg and ac on. It will heat up to 200 when climbing a grade for 5 miles or more in 5th gear and AC on. It will heat up to the same if in traffic with AC on.

pontiac guys talk about the water pump to plate fit needs to be tight, and also, if it is has a later than 69 timing cover, the tubes that go through the timing cover like to leak internally. 68 and older timing covers do not have the tubes.
 
#22 ·
The vacuum advance provides 8 degrees of advance and no need to limit it. I'll back off on the timing to 33 or 34 @ 3k RPM, vacuum advance plugged and try again. I'll also look for a 7 blade fan to replace this 5 blade. Shouldn't this work? https://www.summitracing.com/parts/oer-3991431

It's supposed to be about 10 degrees cooler tomorrow. From mid 90s to the mid 80s. We will then take the car out for a drive.
 
#24 ·
I didn't measure the vacuum can advance, just believed 8 degrees meant 8 degrees at the crankshaft.
The B26 is advertised as 8 degrees. So... If I install a stop, as Dave Ray explained, to reduce the travel by 38%, I'll end up with 10 degrees at the crank and it will hit the stop before the present 13" of vacuum. That should work out well.

I'm still learning. Thank you all!
 
#26 ·
One thing to consider, all GM point vacuum advances need a section of rubber hose over the pull pin that moves the point plate to give the correct degrees for the advance. Aftermarket advances don't have these hoses, easy to do, vacuum hose. This is why an 8 degree aftermarket advance comes up with 20 degrees when checked.

We have all heard someone come up with "I plugged the vac adv into full manifold vacuum, and it ran up 30 more degrees, what goes?" Well, no rubber stop in place, simple. Add tubing, simple fix.

The instructions I posted in the other topic give ways to add the stop with metal pieces, one locked down, the other adjustable, permanent solutions that do not rot away, and/or fall off.
 
#27 ·
Over the years I've studied Johnz's and Dave Ray's tuning instructions. The two documents complement each other and I have them both saved on my hard drive for quick access. I feel I am pretty knowledgeable of tuning but I'm always learning more. This is one of those times I'm learning more.

I saw the 36 degrees come all in before 3,000 RPM and held at 36 above 3,000. I'll remove the vacuum advance and limit it's travel after determining how much it truly advances. I've added vacuum advance limiters before.

I believe the most logical next step will be increasing air flow with a 7 blade fan replacing the 5 blade. It seems, based on discussions and Google search results, the Pontiac 400 has a history of running hotter than the typical Chevy small block.
 
#29 ·
Your engine running at 210* is not far off from factory specks. These engines were designed to run at 195* to 200* from the factory. They came with a 195* thermostat. By the time the thermostat was fully opened your engine was around 200*. Check your radiator cap, make sure your cooling system is functioning correctly and as already suggested a good tune is necessary.
 
#31 ·
The fan shroud does cover the radiator pretty well. It is the factory design. The fan is a little offset in the shroud but that doesn't seem too unusual. The distributor is an aftermarket, similar in design to the factory, but will not allow me to drop the vacuum advance pin out the bottom to remove it. There is a plate immediately below it. The VA is held in place with two button head, allen wrench driven, stainless (non-magnetic) screws. So I couldn't chase after the screws with a magnet if I dropped one and had to use a small allen wrench (3/32 if I remember right) to remove the screws. But after I found it was not easily removed I successfully replaced the screws without losing them. I would have replaced the screws if I had another pair easily available but I did not. So I did not add a stop to the vacuum advance and may at a later date after I remove and disassemble the distributor. Or, if I can locate the correct diameter of rubber hose, as Dave suggested, I might be able to slide it into place without removing the vacuum advance. Good idea, I'll check that option.

Yesterday afternoon the owner and I drove the car about 12 miles. Prior to, and with his help, we bled the brakes, as the SS Brakes 4-wheel disc brakes felt weak. I found the back right caliper with the bleed valve mounted on the lower side of the caliper. It seems it is a stagger-shock brake set installed on the '67 without the staggered shocks. :surprise: Anyway, I removed that particular caliper to orientate it up and completed the bleed. Then reinstalled. For good measure we bled all four corners and now the brakes feel good.

With the timing set at 34 degrees and no other changes, other than what has already been discussed, the temp went to 192, then settled to about 184 +/- a few degrees. I believe we may have this problem licked.

After owning the car for about 15 years through the stages of disassembly and a gradual rebuild this is the first time the owner has ever driven the car, except to or from a trailer. You could see his excitement to really drive his car for the first time. That was a lot of fun and made my day. :smile2:
 
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