# Overheating questions



## 69judge1 (Oct 14, 2018)

Hi all! Just joined this forum and im wondering what your thoughts are on a particular topic. I have a 69 gto original judge not a clone. We pulled the 400, still have it, and dropped in a 455. The problem im having, had the same issue with the 400, is the darn thing runs hot. Most of the time it runs 180 deg when your in traffic or when you shut it off you can watch the temp gauge clime to 220 and above. Mostly wngine is stock, we tried a high flow thermosts, tried electric cooling fans, new larger radiator, an inline coolant pump etc. I hate the overheating issue because it makes the engine very hard to start qhen its warm. It does have headers, and we tried a high torque starter but dont like the sound of it so we switched to an oem high torque starter. Any thoughts on the topic are greatly appreciated! Thanks in advance!!


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## Goat Roper (Oct 28, 2014)

Welcome to the forum.
If you click on the forum page you will see the different posting sections on this forum.
You have posted in the 2004-2006 GTO section so I will move your post to the proper page.
That being said 180 is not overheating for a Pontiac.


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## PontiacJim (Dec 29, 2012)

69judge1 said:


> Hi all! Just joined this forum and im wondering what your thoughts are on a particular topic. I have a 69 gto original judge not a clone. We pulled the 400, still have it, and dropped in a 455. The problem im having, had the same issue with the 400, is the darn thing runs hot. Most of the time it runs 180 deg when your in traffic or when you shut it off you can watch the temp gauge clime to 220 and above. Mostly wngine is stock, we tried a high flow thermosts, tried electric cooling fans, new larger radiator, an inline coolant pump etc. I hate the overheating issue because it makes the engine very hard to start qhen its warm. It does have headers, and we tried a high torque starter but dont like the sound of it so we switched to an oem high torque starter. Any thoughts on the topic are greatly appreciated! Thanks in advance!!



As Goat Roper stated, 180 is not hot and actually pretty good. What you are experiencing when you shut the engine down is "heat soak." The coolant is not circulating so it absorbs the heat rather than pass it along through the radiator for cooling.

Hard starting after it has been shut down and temps rise is typically one of three things. Engine timing, carb leak, or the typical results of ethanol gas - if you are using it. Seeing the car runs at a good temp, I don' think its timing BUT it could be a factor if initial timing is too far advanced. If it is a carb leak, you would smell it coming from the engine bay after shut down. So my money would be initially on the ethanol gas - as long as you know your timing is good. This has been covered here on the forums. Heat will boil/evaporate the gas when you shut it down. You can find/use several methods to minimize the heat that gets under the carb and this may help to improve the problem. :thumbsup:


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## john23 (Mar 6, 2016)

Jim and Goat roper all good info. sometimes heat soak can be helped or cured by putting an electric pump back by the tank. pressurized fuel to the hot mechanical fuel pump boils at a higher temperature so does not vaporize as easily....or by pass the mechanical pump altogether and just run an electrical pump with a regulator.


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## joelau27 (Sep 22, 2018)

Try a 160 stat, also check clearance between divider plate and impeller on the water pump. Try to get a cast impeller versus a stamped steel one. These 3 things will make a huge difference. Ckeck that the clutch fan is operating correctly, and that you have the correct shroud.


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## PontiacJim (Dec 29, 2012)

joelau27 said:


> Try a 160 stat, also check clearance between divider plate and impeller on the water pump. Try to get a cast impeller versus a stamped steel one. These 3 things will make a huge difference. Ckeck that the clutch fan is operating correctly, and that you have the correct shroud.



The OP is not having an overheating problem. Temps are good by Pontiac standards. His problem is the hard starting when the engine is shut down. :thumbsup:


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## geeteeohguy (Feb 2, 2008)

PontiacJim said:


> The OP is not having an overheating problem. Temps are good by Pontiac standards. His problem is the hard starting when the engine is shut down. :thumbsup:


Agree! He is having heat soak issues, very common. Since the starter turns, but slowly, it is a current problem. Possible upgrade to better/heavier gauge battery cables and verify all engine grounds. Also, verify that the initial timing is not too far advanced. A quick test is to crank it with the ignition coil disconnected after it heat soaks. If the engine spins normally with no ignition, you have a timing problem.


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## Datold1 (Nov 27, 2018)

Glad to see this much help and advice. I am having heat problems also. I have a 66 389 Tri-Power with mild cam bored .030 Sealed Pro pistons and rings. I had Dakota digital dash installed. I have flushed and checked radiator installed 2nd 160 degree thermostat, new stainless dividers and Gates cast iron impeller pump, new lower hose with new spring Running Peak 50/50 blend anti-freeze, Have oem fan shroud and even blocked off top area between tank and shroud to force pulling air through radiator instead of over it. Also installed new fan clutch. I drove a round trip of 7 miles and was registering 215 degrees at the end. I know timing is slightly advanced and vacuum advance disconnected because Pertronix ignition was installed I run only 93 octane shell and usually with booster although I don't see much difference. What's left?


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## geeteeohguy (Feb 2, 2008)

You need to run a vacuum advance on the street for engine cooling and fuel economy.


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## PontiacJim (Dec 29, 2012)

What *geeteeohguy* has stated plus, you invested in parts hoping to find the issue, but I did not read anywhere that you purchased one of the inexpensive hand-held laser temperature guns from your local auto parts store to verify what your gauge reads. What if your gauge is inaccurate or the sending unit to the gauge is not exactly matched to it?

Get the laser gun to check engine temps at the upper hose, lower hose, and parts of the radiator for flow.

Air bubble in the coolant system? This can happen. I always pull off the radiator cap when cold, then fire up the engine and watch for the coolant to "move." Once the engine reaches temp (160), the thermostat will open allowing antifreeze to circulate and you will see it very clearly - it should be above the radiator cooling tubes at the top. Allow it to run like this for a short time and watch for any bubbles. Without the radiator cap on, it is possible that any trapped air can be "burped" from the system. I like to drill one or two 1/8" holes in the ring of the T-stat just for this purpose so any trapped air will squeak out even if the T-stat is closed. If all looks good, put your cap back on. 

Not the biggest supporter when it comes to clutch fans. Depending on the brand, some are better. My preference is a flex fan which has no slip and draws air well at lower RPM's. 

If the engine is still fresh with few miles on it, it may still be "tight" and this can add to higher temps. Higher compression will mean additional cylinder pressures which also equals more heat in the engine.

Temps will go up if you drive the car a bit hard and then don't give the engine time too cool down, as in shutting it off early. Temps will also climb once you shut the engine off as coolant is no longer circulating, so this is normal. 

If you don't mind trying an additive, I can say I have used this product in my previous engine build which ran hotter than I liked and it did drop coolant temps down in my engine and ran cooler overall. You won't see drastic changes but every few degrees helps and the product has other properties worth noting. I got mine at my local Advance Auto store. https://www.redlineoil.com/waterwetter 

Timing can affect engine temps. Too much retard and it will run hot. Too much advance can do the same thing. So you might want to play around with this as well. What you do not want is engine "pinging" or "detonation." Not knowing what your compression is, 93 octane may not be enough if you did not drop your compression down to around 9.3ish during the rebuild. .030" over will only add more compression to whatever your stock compression is. Add an aftermarket cam with specs designed to build cylinder pressure, and you may need racing gas.

:thumbsup:


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## Lemans guy (Oct 14, 2014)

Also verify that your fan clutch is a “Thermal” fan clutch that activates as temps rise. There is also fan clutches that will fit and look similar but are RPM activated. The thermal’swork better.

There is number in the clutch on the front near the spring you can see it with a mirror.....see if you can read it and verify....

Make sure, if not a thermal clutch you may want to change it.


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## GTO44 (Apr 11, 2016)

Datold1 said:


> Glad to see this much help and advice. I am having heat problems also. I have a 66 389 Tri-Power with mild cam bored .030 Sealed Pro pistons and rings. I had Dakota digital dash installed. I have flushed and checked radiator installed 2nd 160 degree thermostat, new stainless dividers and Gates cast iron impeller pump, new lower hose with new spring Running Peak 50/50 blend anti-freeze, Have oem fan shroud and even blocked off top area between tank and shroud to force pulling air through radiator instead of over it. Also installed new fan clutch. I drove a round trip of 7 miles and was registering 215 degrees at the end. I know timing is slightly advanced and vacuum advance disconnected because Pertronix ignition was installed I run only 93 octane shell and usually with booster although I don't see much difference. What's left?


Dakota digital temp gauge tends to read a bit on the high side. I just did a 72 cuda with a 440 big block with dakota digital gauges and a holley sniper. At temp the Holley sniper shows around 195 and the dakota gauges show about 204.

Also there’s different opinions about this but i would put a 185 degree thermostat in it. The 160 with manual fan isnt going to cool the water in the radiator fast enough before the thermostat opens again. Thats why on late model cars, we have to reprogram the electric fans to come on sooner when using a 160. 

Most of the time in the dead heat of the florida summer a 185 does better than a 160 at keeping the engine cool with stable temp.


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## dd68gto (Nov 14, 2012)

I owned my first 68 gto in 1974 before I went in Air Force . ( I gave to my mom to drive for four years ) This was a common issue even at 6 years old . All of the issue discussed are problem but what we found is the starter got hot and fried . They did make a heat Shield to deflect some of this heat off the stater but they still had problem. Let it sit for 15/30 minutes and it starts ( sometimes) I can't tell you how many starter I replaced on my back and as some of you know they are a bitch to do from under the car . Very heavy and getting shimed just right was a bitch . I would bet 9 out of 10 start issue were related to bad starter / solenoid. This is my two cents . I now have a 68 gto with 9.4 compression and runs 195/200 all day and have never had a single start problem . My guess is it running cooler and the drop in compression makes it much easier to turn . I'm not saying other issue are not things to look at , but this is my experience with my gto' Doug


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