Yes, another Pontiac 400 overheating question! - Pontiac GTO Forum
User Tag List

 1Likes
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 33 (permalink) Old 02-01-2018, 11:33 PM Thread Starter
 
AJFrechette's Avatar
 
Join Date: May 2011
Location: Oregon
Posts: 27
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Yes, another Pontiac 400 overheating question!

Hi Folks,

Yes, another Pontiac 400 overheating post. I know. Sorry. But, before i begin, a few facts:

I am old. I bought leaded gas.
Grew up in a Pontiac family (Star Chief- grandfather, Catalina wagon - dad, 68 GTO convert, brothers, and several Grand Prix's and Firebirds). Been a car guy pretty much since the beginning. i have managed to rebuild Porsche and Mercedes engines, so I am probably not a total handicap. That said...

So i am pretty sure i have addressed all of the known and possible gremlins...(water pump plate spacing, cast iron impeller, radiator, air flow, radiator fan, shroud spacing, timing cranked to max advance possible, thermostat working right, good top to bottom radiator temp delta T's, flow is excellent) and on and on. The only thing i can think of on this is that the vehicle might be running a bit lean, so i installed an AEM wide band sensor and ran the car across a broad range of conditions (freeway, hard acceleration, part throttle, up hills, over hill, over dale, you name it) and it's running at what appears to be excellent AFR's at all demand levels but perhaps just approaching 14.7 at cruise at highway speeds. One thing i have observed is that the car heats up amazingly fast. Like crazy fast. It can jump to 180 in just a minute or so. Might be exaggerating a but here but i will time it. The car will idle all day in the hottest weather at 180. Get it out on the highway and she gets hot. Question is, how lead does she need to be before she get hot because of a lean cruise mix? I am certainly not above 14.7 at cruise. Probably closer to 14.

Also, probably important to note that it's .40 over and the PO put a cam in it (i will check to see if it's possibly too rowdy when i yank it) but do these blocks start to run hot when they get bored out this far?

My car has a 73 400
.40 over
4X heads with small valves
Stage 1 Quadrajet
HEI from mid 70's Yak but it was set curved by Majhor Murray in PDX (seem competent)
Pretty sure I am getting 32+ degrees of advance but it jumps around a lot
Runs beautifully
TH350
3:23 Rear end

Again, i am yanking the engine to address this mystery leak (car only has 2k on it since rebuild) but i can't deal with leaks. Any advice is welcome at this point. And no, i refuse to put a modern engine in it. Who would give up the sound of a 400 with a quadrajet for that ?

Ideas?

Thanks!

Allen
AJFrechette is offline  
Sponsored Links
Advertisement
 
post #2 of 33 (permalink) Old 02-02-2018, 08:40 AM
 
1968gto421's Avatar
 
Join Date: Mar 2014
Location: Travelers Rest, South Carolina
Posts: 752
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 70 Post(s)
If you haven't already, you may want to look over this forum thread (hope it's helpful):

https://www.gtoforum.com/f178/possibl...heating-15588/
1968gto421 is offline  
post #3 of 33 (permalink) Old 02-02-2018, 05:50 PM
 
PontiacJim's Avatar
 
Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Posts: 3,449
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 347 Post(s)
Garage
Put a Chevy LS3 in it and you will never have problems again........not.

Since you stated that it heats up rather fast, first guess is the timing is retarded. If you have a dial-back timing light, you may want to write down the RPM and your timing numbers beginning at 1,000 RPM's up to your maximum advance RPM's in 250 RPM increments to see what is actually happening within the HEI.
PontiacJim is offline  
 
post #4 of 33 (permalink) Old 02-02-2018, 08:01 PM
 
Join Date: Nov 2012
Location: South of Boston
Posts: 185
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 31 Post(s)
There are a lot of threads on this forum and The PY site. Two things that come to mind immediately are related. Bottom hose collapses on high rpm. The next is related to flow throughout radiator and engine as you get to higher RPM ( possible clogs) good luck and keep us informed. Doug
dd68gto is offline  
post #5 of 33 (permalink) Old 02-04-2018, 10:38 AM Thread Starter
 
AJFrechette's Avatar
 
Join Date: May 2011
Location: Oregon
Posts: 27
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Will do. Flow is good. Lower hose has the coil in it, so it shouldn't be collapsing.

Any thoughts on the .040 over topic? Do these blocks begin to run hot when bored over?
AJFrechette is offline  
post #6 of 33 (permalink) Old 02-04-2018, 11:51 AM
 
PontiacJim's Avatar
 
Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Posts: 3,449
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 347 Post(s)
Garage
Quote:
Originally Posted by AJFrechette View Post
Will do. Flow is good. Lower hose has the coil in it, so it shouldn't be collapsing.

Any thoughts on the .040 over topic? Do these blocks begin to run hot when bored over?
I questioned my machinist about that same thing because I was concerned too. He said "no". The amount of overbore is like the thickness of a human air and not enough to have any effect on cooling. He said if you have cooling issues its not because of the overbore.

You did not provide what "hot" temps mean. What are your actual readings? Perhaps the gauge is incorrect or sending unit is not matched to the gauge. Where are you reading your temps? Higher temps will be read if using the gauge plugged into the side of the head versus the water crossover at the thermostat.

Have you used a hand held digital laser temp gun to shoot the various areas of the radiator & cooling system as well as head/exhaust temps? These will be more accurate than your gauge reading OR can confirm your gauge reading. My '73 Fury gauge reads "hot" and climbs to a level nearing boiling in hot summer heat in stop/go traffic. I did all the checks and replaced a few things hoping to help(which did not) and then got a laser temp gun. The gauge is way off as my radiator temps were near 170 degrees when my gauge reads into the "hot" range.

You also stated the timing jumps around a lot -it shouldn't. Again, check the HEI for issues like sticking weights, worn parts, or bad module. What is your initial timing setting at the crank? How much mechanical advance does the HEI provide? How much advance does the vacuum advance provide? Is the vacuum advance connected to the manifold or ported at the carb?
PontiacJim is offline  
post #7 of 33 (permalink) Old 02-05-2018, 08:53 PM Thread Starter
 
AJFrechette's Avatar
 
Join Date: May 2011
Location: Oregon
Posts: 27
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
All good clues to the puzzle and i will document them all in one place as soon as i get back out to the shop. What kind of exhaust temps would i be looking for at idle? It's pretty cool here in OR this time of year so no amount of gymnastics will heat it up. One interesting symptom is that it's pressurizing quickly...

I will be back...
AJFrechette is offline  
post #8 of 33 (permalink) Old 02-06-2018, 10:39 PM Thread Starter
 
AJFrechette's Avatar
 
Join Date: May 2011
Location: Oregon
Posts: 27
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Ok,

Here are the stats. Again, thanks in advance for any tips.

The initial timing is about 18 BTDC

Total timing is about 32 BTDC

Vacuum advance appears to give about 12 degrees of advance

Vacuum advance looks to be on a ported nipple

Exhaust temps vary from center to ends but it's running 480 on the R, 460 on the L

The heads above the exhaust are at 380

Radiator appears to be pulling about 18F from top to bottom at idle

The timing is not jumping as previously reported...think that's my timing light

Plugs look perfect, if they can be read these days...

Compression is 140, 130, 130, 125, 135, 130, 128, 130

Seems low but I never checked it after it was rebuilt 3000 miles ago

It has low vacuum readings at idle and I don't have a record of what cam is in it, but I will check that when it comes out.

Temp gauge reads accurately

Good lower radiator hose spring

Correct fan blade sits 1/2 way in

Radiator is an original Harrison but was worked on (tanks off) by a reputable radiator guy

Radiator is properly sealed and shrouded

No one has commented yet as to whether or not a close to lean setting will have an effect on running hot at part throttle (highway speeds)...again, it's not real lean but it's close to 14.5 at highway speeds.

So I will report back once I yank the engine and look inside.

Seems like other folks engines don't burn the paint off the heads like mine?
Attached Thumbnails
Click image for larger version

Name:	IMG_1190.JPG
Views:	176
Size:	26.5 KB
ID:	103138   Click image for larger version

Name:	IMG_1191.JPG
Views:	200
Size:	25.5 KB
ID:	103146   Click image for larger version

Name:	IMG_1192.JPG
Views:	206
Size:	37.3 KB
ID:	103154  
AJFrechette is offline  
post #9 of 33 (permalink) Old 02-07-2018, 07:41 PM
 
PontiacJim's Avatar
 
Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Posts: 3,449
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 347 Post(s)
Garage
You did not say if your initial advance taken was with the vacuum advance plugged? 18 degrees initial and with 12 degrees of vacuum advance would indicate that you have 6 degrees initial and 12 degrees vacuum for 18 initial which would mean your vacuum advance is not hooked up to a ported nipple.

If you have 18 degrees advance with the vacuum advance plugged and disconnected, I'd say you have too much initial advance. 10-12 degrees would be better.

Compression can be a function of cam timing - when the intake valve closes. So you could have a lower reading with a bigger cam, but if your vacuum reading is low then you may have a big cam. So what is your vacuum reading?

Air/fuel ratio. You gave us cruising A/F ratio, but what is your idle A/F ratio and wide open throttle A/F ratio?

Have never used an A/F ratio meter, but have on going on my present build. From my research into the best A/F ratio's, I personally feel 14.5 is too lean. I think 13.8-14.0 would be better. Keep in mind that ethanol laced & oxygenated fuels do run leaner by nature and an older type carbed engine should run a little richer using bigger jets, and a bigger cam can increase the need for even more fuel. A lean engine will heat up quick and run hotter. Fatten up the carb and you may see the problem go away.

I found this on the internet: A starting point for A/F mixtures for most mild performance engines is:• Idle: 13.4-14.1; • Cruise rpm: 14.1:1 with a mild performance engine, or 13.4-14.1 with a high performance cam; • Power and acceleration: 12.5:1 for a “normal” engine or high performance engine

You still have not shared what your temperature is that you consider "Hot". But in any case, looks like you have your cooling system well built, so I'd be looking at timing and carb issues to see if any changes can be had.

Could not find a definite exhaust gas temperature as they varied widely depending on cast iron, headers ( coated or not), and RPM's. Your temps may be a little high at 480/460 at idle, but fall into some of the numbers I read off other sites on the internet. So at least the temps are fairly close one side to the other.
PontiacJim is offline  
post #10 of 33 (permalink) Old 02-08-2018, 09:09 PM Thread Starter
 
AJFrechette's Avatar
 
Join Date: May 2011
Location: Oregon
Posts: 27
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Hi Folks,

Ok, sorry, i will fill in a few of the blanks.

The initial timing was taken with the vacuum line disconnected and plugged.

Vacuum reading is about 14 at idle.

WO throttle AF is running in the 12's, so that feels pretty good. The car pulls well.

My part throttle ratio is closer to 14.5.

As far as my definition of hot, it will run up to 200 quickly on the freeway, sometimes hotter. It never really gets hot here, so 90F ambient is probably all it sees.

I will report back when she comes out. I am going to be happily embarrassed if there's a mechanical issue with the flow. But given the low vacuum readings I am guessing the previous owner put a big cam in it. I am going to swap out the 4x heads with small intake valves for a set of 6x heads with a smaller chamber volume and larger intake valves. Not sure i am going to see a huge improvement but since i have them....

When i get on the other side, i will contemplate bigger primary jets!

Thanks for the tips.

Allen
AJFrechette is offline  
Sponsored Links
Advertisement
 
Reply

  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Pontiac GTO Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 4 (0 members and 4 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Newbie here with a pontiac 400 question Tafc18 1964-1974 Tempest, Lemans & GTO General Discussion 7 01-27-2016 08:45 PM
Question on Pontiac 400 Blocks mrvandermey 1964-1974 Tempest, LeMans & GTO Technical and Electrical Wiring 13 03-18-2014 01:04 AM
overheating 400 1967 goat670 1964-1974 Tempest, LeMans & GTO Technical and Electrical Wiring 20 11-07-2013 09:25 AM
overheating 400 1967 goat670 1964-1974 Tempest, LeMans & GTO Technical and Electrical Wiring 14 07-18-2009 08:47 PM
69 gto 400 overheating - need help! jwgto 1964-1974 Tempest, Lemans & GTO General Discussion 7 12-31-2008 07:40 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome