[Vet65te]

Hi All,
The car is a '64 GTO and only has about 150 miles on it so far since a complete makeover (body, paint, drivetrain, etc). The problem is that the newly built engine get's hot, not real quickly but rather slowly but it keeps on going up and up.

Let me run down the whole deal first before I get to the reason for the question on jetting.

Original 389 that's now .040 over.
Stock heads that have been surfaced (probably three times).
Compression is around 10 to 1 since I used cast replacement pistons (not the 8.6 variety).
Cam is a mild Speed Pro with 214/224 duration.
4 speed car.
Exhaust Headers ceramic coated with 2.5 primary pipes to 2.25 Flowmasters and 2.25 tail pipes.
Recored stock 3-row radiator (tall core support), with fan shroud and 7-blade stock fan with new clutch. Actually, have used two different new clutch units with no change in engine temps.
I have performed the water pump/diverter plate mod and reduced the clearance to around .050 tops.
Timing was around 6 to 8* initial with 12* added by the Accel adjustable dist vac pod.
Moved timing to 14* initial with 12* added by vac pod...still overheats.
3x2 center carb mixture screws were out 1.5 turns and I got a reading of around 17 inches steady.
Opened them out to 2.25 turns and got maybe a 1/4 to 1/2 inch more vacuum but again steady.
Street driven car with 3:23's.
Have 16-inch DeRale Electric Fan set for around 200 degrees.
I've also verified with 'Block Check' that I don't have any combustion gases present in the coolant.

Here's the story. Car runs well, no problems no hesitation, no issues...but it overheats. Maybe I should say it likes to get warm and while it will slowly climb if there is no vehicle movement, steady cruise will still see it stay in the mid 190's.
I have verified the temps shown on the AutoMeter gauge with my Raytek IR Gun.
The plugs are #86 Autolites and I've pulled them to see how they are at least three or 4 times and each and every time, they are pure white. I mean, they look as good as ones just out of the box. That's why I richened up the mixture screws from 1.5 all the way to 2.25. It idled smoothly at both settings although, as mentioned previously, I did get a tad bit more vacuum (1/4-inch tops) from the additional 3/4 turn outward. Plugs still look pure white. Driveability, even with these bleach white plugs, is fine but at rest, either idling at a stop light or just idling in the driveway, it will slowly climb up to 210 and unless I shut it off, it would keep on going(electric fan disconnected for test purposes). I do suspect that some of the heating issue is due to a tight new engine but...

I know the rule of thumb is that overheating at idle or very low vehicle speeds is typically attributed to lack of adequate air flow. I'm considering a swap to a fixed flex fan and eliminate the clutch unit...at least for now even though I think that's a real shot in the dark and don't hold out much hope for that move. The other consideration is that it's just running a bit too lean.

Jets are bone stock from '64. These are original carbs that I rebuilt and all settings are as they should be.

So, the question I have is this...with an engine like this that is not modified very much, would you think it might need to be richened up on the primary carb?
Who sells them and what number (richer) would be recommended?

[Hurst65]

My engine did the same thing after I rebuilt it.
My car is very similar to what you have listed. I have a 3 core without a shroud.
I think it was because the bearing clearances were on the tight side. The machine shop that did the machine work machined it that way. After it broke in good it felt like it loosened up and ran cooler. Understand what I mean??

Don't change to a flex fan. They are noisy and take more power to turn at high RPMs. The factory clutch fan set up is perfectly fine.

I would change the jets up a few sizes. See if that helps.

[LPete]

Main jets don't affect idle mixture, and I don't see a mixture problem causing overheating at idle. If it's a manual transmission, I'd suggest speeding the idle up a little -- maybe 50 or 100 RPMs. I don't really think you have a problem (210° is not abnormal). I wouldn't worry 'til at least 220 and still climbing. Will the electric fan keep it cool?

[Bronze66]

I went thru the same thing last year. Found most 180* thermostats are junk, and don't open until 185/190.Bought a Robert Shaw. Controls it good. Main fix was going to an A/C wp pulley. The smaller pulley will get the hot water out of your motor faster and keep it from heat soaking. Provided your rad is up to the task.

[Vet65te]

Hey Guys, thanks for the replies.

Hurst65 - I've built numerous Chevy engines and any that seemed to have a tendency to get warm (maybe one or two out of about 7) after the rebuild got over it within a thousand or maybe two thousand miles of driving, tops. How long did it take your's to 'settle down'? I agree with the comment about the flex fan. Within this 150 total miles, I've swapped the clutch unit to a different brand and it's a slight bit better as far as 'perceived lockup when temps rise' but thought that I'd try something else like the flex fan since I haven't been able to pin down the culprit(s) causing the heating up.
Eh, I'm might not in the end.

LPete - I did know that 'main' jets weren't a heavy influence to the idle circuit but since the mixture screws control more than just fuel I thought I might be able to add a bit more fuel to the fuel/air mixture by going up on the jet sizes. As I mentioned, I started out at the popular base setting of 1 1/2 turns out on the center carb screws and have opened them up to 2 1/4 with very little change to be seen. The plugs are still bleach white. The idle rpm according to the AutoMeter tach inside reads about 800 rpm. At the same time, the old Penske clip on tach/dwellmeter I use under the hood reads about 750 rpm. It's nice and steady and has been with both the 1.5 and 2.25 mixture screw settings. As for the 210 degrees, I did not continue the 'test' any further. With an ambient temp of only the high 60's outside here in Northern Calif, the car was slowly but surely rising and if I had continued, I have no doubt I'd see 220 and more. The 16-inch electric fan I installed kicks on at around 195/197. I had some 'issues' with BeCool on this unit because their advertisements say it can be activated at 160 degrees. Not a damn chance. I had to to move their probe from the suggested middle of the core (down a few inches from the top tank) to just under the top inlet tube. In any case, when it kicks in the temps are somewhat halted. On a cool day it might start to drop a little bit but more likely it will just stop it where it is.

Bronze66 - I knew that when I wrote my initial posting I'd forget a few things. The old thermostat (180*) used to open at around 177 to 178 but after reading all the comments on this forum, I went out and picked up a Robert Shaw Hi-Flow. It's also a 180 but seems to have a slightly higher opening point of around 184/185. I did that little addition at the same time I did the water pump/diverter plate adjustment and honestly can't say that there's been any change at all. I do think the 3 row radiator should do the trick, granted there are better versions out there but it's not like I've got some firebreathing engine under the hood. It's basically a warmed over 389 with a mild cam and headers so I think it should be okay. Can you tell me which A/C applications got that pulley you mentioned?

Thanks

[goldeneyee]

Looks to me that your mixture is way too lean for todays gasoline. Jets are available through our sponsor. Easy enough to change--I would go a step or two richer. 190 isn't all that bad considering the overbore, 3 core and running lean. Next time, go to a high efficiency 4 core....

[LPete]

Originally Posted by Vet65te

LPete - I did know that 'main' jets weren't a heavy influence to the idle circuit but since the mixture screws control more than just fuel I thought I might be able to add a bit more fuel to the fuel/air mixture by going up on the jet sizes.

They have NO influence on idle mixture. Their job is to meter fuel when the main circuit comes into play, with the throttle open. The idle fuel in some carbs passes through them (not sure about the Rochester 2 bbl), but when it does they present no restriction to the small amount of idle fuel.

The small amount of air added to the idle fuel is mainly to atomize it better -- the mixture is still mostly fuel. When you richen the idle mixture screws you're really adding fuel, not a significant amount of air. If you added a lot of air the idle speed would increase as you kept richening it.

I really don't think the fuel mixture will affect idle coolant temp at all. When extra fuel is used for cooling it's under heavy load conditions, when a large amount of fuel is flowing, and it helps carry combustion heat out the tailpipe. The exhaust gas temperature at idle is very low, regardless of mixture.

If it were mine I'd drive it for awhile and see what happens before I'd spend a lot of time chasing something that might fix itself.

[Vet65te]

I agree that more miles should help the situation, it's just that this is my first Pontiac and I've never had an engine come up on temps as fast as this one seems to do.
I don't like to throw a lot of parts on it in an attempt to fix it and do think that the current setup is not 'broken'. But on the subject of mixture screw settings, I will try to open them up a bit more to see what happens. I typically make a single change and then see how it reacts before I make any further changes. Oddly, the engine had a smooth idle at the 1.5 idle mixture setting as well as the next two, at 1 3/4 and 2 1/4.
While there was a slight bit more vacuum and idle rpm, it was still smooth and the vacuum reading has been steady at all idle settings. I also realize that sparkplugs don't 'color' like they used to back when we had tetraethyl lead and other additives in gasoline but seeing these plugs looking bright white still makes me think it's running lean.
And in the relatively few 150 miles I've put on it since completing the car, a whole bunch of that run time has been idling in the driveway.

[Hurst65]

It did not take too long for it to "settle down". It just kind of happened over the course of getting all the bugs out of it and tuning it. My cam is alot bigger than the one your running so I had a difficult time tuning it. I had to enlarge the tubes in the cluster to get it to run right.
I agree with Lee, drive it for a while and see what happens.
I have a 3 core with no shroud (I want one) and unless I'm in heavy traffic for a long time on a hot day it stays around 180-190. This is with 11:1 and a xe284 cam.

[LPete]

Originally Posted by Vet65te

Oddly, the engine had a smooth idle at the 1.5 idle mixture setting as well as the next two, at 1 3/4 and 2 1/4.
While there was a slight bit more vacuum and idle rpm, it was still smooth and the vacuum reading has been steady at all idle settings. I also realize that sparkplugs don't 'color' like they used to back when we had tetraethyl lead and other additives in gasoline but seeing these plugs looking bright white still makes me think it's running lean.
And in the relatively few 150 miles I've put on it since completing the car, a whole bunch of that run time has been idling in the driveway.

The vast majority of extra heat produced by a newly built engine is caused by piston ring/cylinder wall friction, which will decrease as the rings break in. Idling does very little to break in the rings -- it really needs to be driven under moderate load. If the bearings have extra friction you've got problems.

As far as idle mixture affecting idle speed, the idle speed on any engine drops off rapidly when the mixture is lean of stoichiometric, but it has to be extremely rich before it drops much. There's a wide mixture range where the idle speed (power produced by the engine) stays fairly constant -- only the carbon monoxide goes up due to not enough oxygen for the amount of fuel burned.

[440GP69]

That comp with that cam without 100 octane racefuel hmm i don't think any amount of tuning will fix that might check the bearings to see if they are hammered from detonation, yes it can be inaudible, IMHO and experience i would not go over 9.4-9.5:1 max with 92octane

[Vet65te]

The more I talk with you guys, the more I find myself coming back to the engine just being fresh and exhibiting a bit more friction than I'm used to. I did the engine assembly and did use plastigage on the mains and they were within specs. Since it was a while ago (hey, I've had this car for 14 years and just late last year got it completed) since I put the engine together, I can't remember if I just plastigaged one or two of the rods or if I did them all. I'm thinking I did only a token one and maybe two. I do definitely remember rotating the assembly after each one was installed to make sure I didn't nick something and there didn't seem to be any 'extra' tension needed to make the crank assembly turn.

As for the correctness of the mixture settings, that is a good idea to verify actual CO and HC readings in order to take all the guesswork out of it. I do have a cheap CO tester that works fairly well but might just find one of the local smog-test-only stations and have them run a tape for me at idle and say 2500 rpm to see what it's actually doing.

Thanks again for the help, I'll keep you all posted.

[Vet65te]

440- Until today's timing change the initial has been at around 6 to 8 degrees with the Accell vac pod set at 4 turns which comes out to about 12 degrees added by the manifold vacuum. So, it was really running only around 20 degrees as opposed to the stock setup which had 6 degrees initial and I think about 20 degrees kicked in by the factory vacuum pod. Yes, I do understand that knocking can be inaudible but this engine has been whisper quiet at that setting and even at the new setting of 14 degrees initial (with the same 12 degrees at the vac pod). As for the compression ratio, I did check the deck height clearance at TDC when I put it together but don't recall the number right now. I suppose I'm on the high side of 9.5 but maybe not by a whole bunch seeing as how replacement pistons are typically built with about 5-thou less deck height than the stockers were to supposedly compensate for block decking and head surfacing, which was done. Also, using a relatively thick head gasket instead of the steel shim gasket the factory used might also work in my favor.
In the end, I don't see the compression which might be hovering around 10 to 1 as being responsible for this heating issue.

[440GP69]

does the temp change when you change the timing? having it too retarded will also caus it to run hot, what thermostat if any are you running?, i'd say you are pushing it comp wise but if you can get away with it awesome!

[Bronze66]

vet65 we have about the same combo engines (389). I had a large 5/16 tube 3 row rad. (original) I went and had it recoreded to a high efficient 4 row. It added 96 more tubes. That still didn't do it. My stock wp pulley was an eight inch. I went with the seven inch a/c pulley. THAT fixed the problem. Even in 100* weather sitting in traffic it will creep up to 200-215. As soon as I start to move,even slowly it will drop back down to 190/195. Your carburation sounds like it's fine. I went down and looked at the pulley numbers. They are 8"- 9778808, 7"- 9782679 XJ and 9786909 XJ. The 7" numbers may be two different years. If you want one of my extra 7" let me know. $20 w/shipping. My Shaw stat doesn't let the motor run cooler than around 182. But basicly no hotter than 195.

[Vet65te]

When I rechecked the timing yesterday (total mileage was about 140) I found the initial set at around 6 which is about where I set it to begin with. I jacked that up to about 14/15 initial, with the same 12 degrees added by that adjustable Accell dist vac pod, but there was no difference to be seen as far as temps were concerned. Big let down.
After racking my brain on all the possibilities of what could be causing the engine to get hot slowly but surely I was down to two possibilities, the timing and mixture settings.
I think the car 'feels' a bit snappier with the extra 8 or so degrees but nothing monumental, just a little bit better. I knew that retarded timing exposes more of the combustion to the cylinder walls and can cause heating problems but in the end, it's like it had no effect at all.

As for the potential compression problems, after raising the timing yesterday I tried to enduce some 'rattle' out of it by short shifting and giving it a bit more throttle and thought it sounded okay but yesterdays temps were only in the high 60's and there really wasn't much of a load on the car with only me in it and driving casually on a flat road so I may back off the initial from the current 14/15 down to 10 or 12 just to be safe side since the extra timing didn't perform that 'miracle' I was hoping for.

[Vet65te]

Bronze - Does the 7-inch pulley have the exact same 'offset' as the stock 8-inch pulley?

[Bronze66]

I forgot to say my motor was newly rebuilt at the time. (last year) I'm running 9.4 cr. The other config I had was 9.7 cr. Never had a problem with cooling or detonation. I run 89 octane now with out a problem. I don't believe in this silent detonation b.s. Detonation no matter how small still makes noise. I think most people have to loud of exhaust or the radio is up. I ran 10.7 cr (measured) with the original heads on 93 octane. Had bad valve guides so there was oil contamination. That's where I learned how to deal with detonation.
I took the motor apart last year it had about 65k miles on it. Some of the rod bearings had lost some of their crush. But no real signs of detonation damage.

[Bronze66]

Yes same offset. Becareful a 400 ci motor has a different (more) offset than the 389. Not sure about the 67 year 400. It may be the same.

[Vet65te]

Bronze66 - Until I started this thread, I didn't know that A/C cars had a smaller water pump pulley which I suppose was intended to speed up both the water pump and fan and that might be helpful in my case since the temps typically stop climbing when I get underway. Now, it doesn't drop down in temperature at all but the added airflow does obviously make a difference as does the 16-inch fan when it comes on.
I'll send you a PM on the 7-inch pulley. Thanks