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#1
03-07-2020, 11:38 AM
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Over heating while driving on freeway.
I know this subject has probably been beat to death, but i'm ready to beat it some more...
I have a customer bringing me a 68 firebird with a fresh 455...He says the car never overheats during city driving, but will immediately overheat on the highway...Says he can pull over and it will cool right back down... Its been to several other shops, with no luck...They have supposedly done all of the normal things, water pump swaps, new separator plate, thermostats, etc... I'm leaning towards it being a timing/carb issue... |
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#2
03-07-2020, 11:55 AM
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Timing could be set too low if the engine pings on pump gas. If it has factory type exhaust, with heat riser valve for the cross-over, make sure it's open. Clay Last edited by "QUICK-SILVER"; 03-07-2020 at 12:01 PM. Reason: little more |
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#3
03-07-2020, 12:13 PM
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does the lower hose have a reinforcement spring inside?
it may be collapsing... |
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#4
03-07-2020, 12:15 PM
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Are both cover plates installed at the top of the radiator support?
Here’s a ‘68 I recently sold, both plates are missing in this picture.
__________________
1964 Tempest Coupe LS3/4L70E/3.42 1964 Le Mans Convertible 421 HO/TH350/2.56 2002 WS6 Convertible LS1/4L60E/3.23 |
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#5
03-07-2020, 12:24 PM
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Those are some great ideas guys...It'll be here tomorrow, so i'll let you know what I find...
Thanks for taking the time to post. |
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#6
03-07-2020, 12:55 PM
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As always, the first thing to do is get an infrared thermometer and check the temp gauge.
__________________
 1965 Pontiac LeMans. M21, 3.73 in a 12 bolt, Kauffman 461.
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#7
03-07-2020, 02:58 PM
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#8
03-07-2020, 08:11 PM
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#9
03-08-2020, 04:36 AM
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Check that vacuum advance is connected...& working. Engine needs extra timing at cruise to run cool.
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#10
03-08-2020, 08:58 AM
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Quote:
Bingo
__________________
🧩 Burds Parts, Finding those Hard to Find PCs, no Fisher Price Toys Here Just Say No To 8” Flakes F ire B irds 🇮🇱 |
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#11
03-08-2020, 11:44 AM
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Is it actually overheating? Like as in boiling over? How long before it has to be shut down? What kind of fan shroud combination does it have?
I know it's a fresh rebuild but you should get it tested for a head gasket leak as well as the other suggestions.
__________________
--------------------------- Fool Around, Get Hurt, Don't come Crying to me. |
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#12
03-08-2020, 11:52 AM
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As for the shrouding...Its not here yet, but he said they have tried different shrouds, fans, etc...I'll know more when it gets here. |
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#13
03-08-2020, 12:17 PM
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__________________
--------------------------- Fool Around, Get Hurt, Don't come Crying to me. |
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#14
03-08-2020, 12:56 PM
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This is the problem with most discussions...If he continued to drive, it'll boil over and tear it up, and we all know that...So, rather than try to talk about 220 is not "over heating", lets stick to what I posted... Now, while I know you'll think i'm being an ass for saying that, think through what I have said from the start of this thread...I will do the head gasket checks along the way, but based on what he has told me, it doesnt seem to be a head gasket...He can make hard 1/8th mile hits, with no issue...I would expect a head gasket to show signs under full throttle pulls like that...But, it will get checked out too... Again, it only stops climbing due to the fact that he pulls off the highway... |
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#15
03-08-2020, 03:28 PM
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What your symptoms mean to me is that there is not enough air flow at higher speeds seeing it cools down at lower speeds where I am assuming a good fan takes over and draws enough air through. Couple of quick checks that may seem simple - is the anti-freeze the correct mix? 50/50? Is the radiator cap good, sealing, and 15 PSI? Keep in mind that the expansion tank does not get filled to the top on the older cars. If you do, they will push coolant out until it "normalizes." The factory manual, as I recall, says it will be 2-3" from the top. The cooling tubes should be covered. Have you pulled the cap when cold and observed the coolant flow while looking down into the expansion tank? You should be able to see the coolant sitting steady, not flowing, when cold, and then watch is slowly begin to flow as the T-stat opens, and then flow well once it reaches full temp based on the T-stat temp. A slipping belt. Yep, had that happen. The belt appears to set in the pulley correctly, but in fact is set too deep and is riding on the center of the pulley instead of the pulley grooves/sides. So at higher RPM's, with more grip needed to rotate the fan, the belt is actually slipping around the pulley center. You won't hear any squealing or signs of a problem because it is rotating, just not grabbing. The replacement belts are often metric and not correct for our old car applications. I found that the Dayco top-cog belts worked best for me and sat in the pulley groove where it should and ot down low in the pulley groove riding on its center hub slipping away. That said, first thing would be to have the radiator boiled out and checked. I did not see this mentioned by you. If by chance you have an aluminum radiator, it could be possible that the tubes are too small or too tightly placed together to provide sufficient cooling/air flow. Either way, I would still have it boiled out and tested as it is possible that there is junk in it even if new. Next, is the thermostat. I have had the experience of brand new T-stats, made overseas crap, go bad shortly after installation. I don't think they use the best quality metals and after a couple cycles of open/close, they fatigue and stop working. I use a 160 degree T-stat and I am going to get flak that it is too cold, the engine doesn't get hot enough to rid the oil/engine of moisture, you heater won't get too hot in winter, and anything else that critics can come up with. So get a 160 T-stat if you are already not using one. But, what you want to do is drill two (2) 1/8" holes in the brass ring between the center and outer rim - where you won't be causing any sealing issues. Why? This allows trapped air out which can create a bubble in the cooling system and cause it to run hot/overheat. It can also be in your favor should the T-stat close down if it fails and allows the cooling system pressure through, however small, and won't puke explosively back out through the engine, bottom hose, and out the cap. My experience has also been that the overheating, which it is going to do if the T-stat collapses, will rise steady, but slower and give you just a little more time/edge to get to a safe place. You can also purchase a T-stat having the pressure relief valves built in. Here is an example of the Milodon high-flow 180 degree T-stat with the brass relief valves built in. https://www.jegs.com/i/Milodon/697/1...SABEgI77vD_BwE Here is the 160 T-stat, but does not show the brass valves, but assume they are there, so you may want to inquire if you go that route: https://www.jegs.com/i/Milodon/697/16400/10002/-1 Other suggestions mentioned are good things to look into. Bottom hose collapsing at higher speeds as the water pump turns faster and can cause enough suction on the lower hose to collapse. If you do not have a hose with the spring/expander inside to keep the form of the hose round, you can either purchase a hose with the spring/expander or jut buy the spring and install. It could be a timing issue, ie too much advance, both mechanical or vacuum. Check the initial at the balancer, then determine the distributor's advance curve and what the RPM is that full advance (balancer + distributor weights) come in at (with the vacuum advance disconnected). The total may be coming in too soon for that engine combo. The vacuum advance should be used for a street car and can provide better gas mileage along with engine cooling at part/no throttle driving. But, if the mechanical is way too high, the vacuum gets added to this and can aggravate the problem rather than help. If the engine is running too lean it will heat up. You may have a mixture that works at lower speeds, but once the RPM's increase, not enough fuel is getting to the engine causing it too lean out - which means running hot. The carb could be clogged somewhere or jetting too lean. Other things to check could be the fuel pump not delivering enough fuel at higher RPM's, the "sock" at the end of the pick-up tube in the gas tank has collapsed or is plugged, wrong gas cap and the tank is not venting creating a vacuum inside it and not allowing enough fuel to flow through the lines, cracked/split rubber lines letting air in rather than the needed fuel at higher RPM's. Camshaft not dialed in correctly. The intake and exhaust valves not closing at the right time, ie jumped timing, cam installed using wrong cam key position, cam gears off a tooth or two when installed. Sloppy/worn timing chain/gears. If factory chain/gears, they used a nylon coated cam gear and it wears out around 60K miles and should be changed. So there could be a number of things to check. Just have to check step at a time and not to many changes at any one time. Sometimes to know what it is, you have to rule out what it is not. |
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#16
03-08-2020, 04:18 PM
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Have you checked how efficient the radiator is at idle?Get a lazer heat gun and see if you have at least a 40 degree drop from where the water enters and leaves the radiator.Tom
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#17
03-08-2020, 04:25 PM
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I also did not notice that he was running ok under full throttle situations. So I would now be less suspect of a head gasket leak as well. I'd now start looking at the suggestions mentioned but I'd also start asking about what kind of radiator is being used. If it's clogged or undersized, that's exactly the symptoms I would be expecting. If the radiator is clean and high capacity, although not out of the question, it's not common for a thermostat, bad fan shroud, missing spring in hose or even timing to run the temperature to a boiling point. . .
__________________
--------------------------- Fool Around, Get Hurt, Don't come Crying to me. |
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#18
03-08-2020, 04:34 PM
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Ok, car made it here today...
It has a wide 4 core brass/copper radiator, with a pair of electric fans that are made to a shroud that completely covers the core... At first look, it doesnt look like it has the plate between the pump and timing cover...It is an aftermarket cover, so i'll have to figure that out first... Its a really nice 68 convertible, that the guy has spared no expense, but it seems he had it at a few shops that didnt care about quality... I'll let you guy know how it goes, and I do appreciate all of the opinions... |
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#19
03-08-2020, 08:44 PM
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__________________
- Mike  '69 Firebird 400 - Goldenrod Yellow, 455 +.060, '6s-7' heads, Comp Cam 276AH-10 (51-309-4), TH400, Ford 9-inch w/3.08, 800cfm Q-jet, Stock Intake, Hooker Headers, Flowmasters '68 Coronet 500 Convertible - Medium Gold Metallic, stock 318 +100,000 miles |
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#20
03-08-2020, 09:01 PM
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Used on 400 cars as well from what I’ve read. Main point being is get some plates if it’s not originally equipped with them, they’re definitely needed for a car with a 455.
__________________
1964 Tempest Coupe LS3/4L70E/3.42 1964 Le Mans Convertible 421 HO/TH350/2.56 2002 WS6 Convertible LS1/4L60E/3.23 |
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