Author Topic: Running Hot?  (Read 3838 times)

Vince

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Running Hot?
« on: July 19, 2014, 11:10:04 PM »
I wanted to post this info to get some helpful feedback and perhaps new ideas, and just to put my mind at ease.  My 1969 Z/28 seems to me anyway to be running hot even though the temp gauge shows well within the standards, reading barely over the first quarter of the gauge when driving and only going to the halfway point after shutting the engine off when I am guessing heat soak comes into play.  Sometimes when I pull away from a stop after driving for a half hour the car bucks, backfires, and then stalls.  I can't get it restarted for about 15 minutes until it cools down.  When I open the hood it is like I can feel a blast of hot air.  Previously the heat riser valve was stuck closed, but I had the flapper taken out.  Wouldn't this mean that no more hot exhaust gases are being circulated up to the intake manifold anymore to warm the carb at start-up?  When starting the car cold it does take longer to warm up now. 
Is it correct that the sensor for the temp gauge is in the engine block?  Is it possible the heads and intake manifold are getting hot for some reason even though the gauge reads fine?  Could there be gunk blocking a coolant passage in the engine, fan clutch not working,  smog pump or AIR system not working properly, etc.? 
About 2 weeks ago I drove it only about 2 miles at no more than 35-40 mph.  When I got to my driveway and turned the engine off and opened the hood I could see heat waves coming up from the passenger side exhaust manifold.  It was a hot day, in the low to mid 90's.  None of my other cars, or truck, put out anywhere near the heat that my '69 Z does.  And yet the temp gauge still reads fine; could the temp gauge be inaccurate?  My own thought is that I am boiling the fuel in the carburetor even with a heat shield, and that is why it wants to stall or kill and is so hard to restart until it cools down.  Am I overreacting or misinterpreting something?  Thanks guys for any and all help and ideas. 

z28z11

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Re: Running Hot?
« Reply #1 on: July 20, 2014, 01:40:43 AM »
Temp gauge is in the head. I always ran an aftermarket Stewart Warner in the intake close to the water outlet, mechanical gauge. 180 thermostat would always give me 180, no more.

Check your fan clutch, run a dose of cleaner through the whole system, dump and refill with 50-50 Prestone or equivalent. Older radiators over time will build up an incredible amount of scale in the lower tubes: if you haven't rebuilt the core, you might do so if all of the other remedies don't affect it. Drop in a new thermostat when you clean the system, and always run a thermostat - the restriction it offers to water flow slows down the flow enough to let it pick up more heat for transfer at the radiator. After you have checked all of the above, get yourself an inexpensive infrared handheld thermometer and check the radiator, engine block and heads for hot spots. Rebuild your water pump if you're unsure of it - sometimes the impeller can wear down and lose efficiency over time. You can also use "water wetter" additives, that allow the water to pick up more heat as it flows through the system.

Did you use block off plates for the heat riser ports on the manifold gasket ? I always do to keep the temp away from the carb and gas. Check your mixture, especially if you are running a working A.I.R. pump - too lean on today's gas can make 'em run hotter, too.

One thing I hate is an engine to run warm - I don't like to think of what heat does to an engine for life expectancy -

Regards -

1968 Z28 M21/U17 BRG/W
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06

janobyte

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Re: Running Hot?
« Reply #2 on: July 20, 2014, 03:16:15 AM »
Temp gauge is in the head. I always ran an aftermarket Stewart Warner in the intake close to the water outlet, mechanical gauge. 180 thermostat would always give me 180, no more.

Check your fan clutch, run a dose of cleaner through the whole system, dump and refill with 50-50 Prestone or equivalent. Older radiators over time will build up an incredible amount of scale in the lower tubes: if you haven't rebuilt the core, you might do so if all of the other remedies don't affect it. Drop in a new thermostat when you clean the system, and always run a thermostat - the restriction it offers to water flow slows down the flow enough to let it pick up more heat for transfer at the radiator. After you have checked all of the above, get yourself an inexpensive infrared handheld thermometer and check the radiator, engine block and heads for hot spots. Rebuild your water pump if you're unsure of it - sometimes the impeller can wear down and lose efficiency over time. You can also use "water wetter" additives, that allow the water to pick up more heat as it flows through the system.

Did you use block off plates for the heat riser ports on the manifold gasket ? I always do to keep the temp away from the carb and gas. Check your mixture, especially if you are running a working A.I.R. pump - too lean on today's gas can make 'em run hotter, too.

One thing I hate is an engine to run warm - I don't like to think of what heat does to an engine for life expectancy -

Regards -



Ditto.

John Z has a good article on cooling systems in this site.

JohnZ

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Re: Running Hot?
« Reply #3 on: July 20, 2014, 03:31:18 PM »
'69 Z/28
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hotrod68

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Re: Running Hot?
« Reply #4 on: July 21, 2014, 05:25:55 AM »
If it isn't puking any water, I'd change the coil. This sounds like a classic case of the ignition coil overheating, then working once cooled down. Just a thought and good luck.
HotRod'68  1968 SS350 coupe undergoing frame-off resto/rod. 386/350/4.11s
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Mike S

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Re: Running Hot?
« Reply #5 on: July 21, 2014, 01:44:41 PM »
If it isn't puking any water, I'd change the coil. This sounds like a classic case of the ignition coil overheating, then working once cooled down. Just a thought and good luck.
 I have seen that happen with my fathers '66 Mustang. It was easy to narrow down because when the car was hot and no longer would start, the spark was weak and yellow in color instead of a strong 'snap' and blue in color. Changing the coil fixed it.

Mike
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Stingr69

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Re: Running Hot?
« Reply #6 on: July 21, 2014, 02:18:45 PM »
Timimg retarded? 

I would use a stainless steel shim to block the heat passage in the intake manifold/head on the drivers side only.

Do you have an Infra red heat gun to verify the actual temperature?  Nice to have or borrow.

-Mark.

JohnZ

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Re: Running Hot?
« Reply #7 on: July 21, 2014, 02:26:30 PM »
smog pump or AIR system not working properly, etc.?   It was a hot day, in the low to mid 90's.  None of my other cars, or truck, put out anywhere near the heat that my '69 Z does.  And yet the temp gauge still reads fine; could the temp gauge be inaccurate?

If your A.I.R. system is still functional and the rubber diaphragm in the diverter valve has failed (and almost all have failed), the valve defaults to the open position, which blows air into the exhaust manifolds all the time, under all conditions. That will cause hotter exhaust manifolds, without any affect on coolant temperature.

Rule #1 when diagnosing a potential cooling issue is to make sure you really have a problem before you start throwing parts and money at it; verify your temp gauge accuracy with an I.R. gun before you do anything else, as noted in the cooling article I posted a link to earlier.
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Vince

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Re: Running Hot?
« Reply #8 on: July 21, 2014, 05:24:26 PM »
Thanks guys for all your ideas and responses.  I do have an infrared gun so will start from there trying to narrow things down as I go.  You guys have given me some things to look at that I never thought of.  Thanks JohnZ for the article; it was very informative.  It might take awhile for me to check everything but will let you guys know what I find out. 

I did want to ask one more question.  Will blocking off the heat passages in the intake manifold still make a difference even with my car not having a flapper anymore in the heat riser valve? 

I guess what got me the most perplexed was that with all this (in my opinion anyway) excessive heat build-up and hard starting if the engine stalled, the temp gauge still showed well within the normal range. 

janobyte

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Re: Running Hot?
« Reply #9 on: July 21, 2014, 07:26:07 PM »
You want a manual gauge or IR ( or both!) to verify temp first. After readings are obtained, trouble shooting can begin to narrow down problems. If in fact your coolant is normal but under hood temps are increased due to hotter exhaust manifolds (as John stated)....for starters...take off your air cleaner and give the accelerator pump a few gentle pumps with your finger to see if anything is coming out of the primary squirter. (vapor lock, boiling off fuel ?


Coil can be bench tested--heat increases resistance in electronics. It does mimic a bad coil, but what's increasing the heat, and how much?

To sum it up...hot, dense air is bad news for these quasi race 302's...any engine for that matter (those scoops are not just decoration) Todays engine management systems(computer) re tunes for conditions as needed.

Post some temperature readings ,everyone will figure it out pretty quick.

hotrod68

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Re: Running Hot?
« Reply #10 on: July 22, 2014, 03:23:06 AM »
  Blocking off the manifold heat ports will stop the choke from working right if you have the spring/lever choke. That heat is what acts upon the spring and moves the choke flap open as the car warms up.
HotRod'68  1968 SS350 coupe undergoing frame-off resto/rod. 386/350/4.11s
Butternut Yellow    black standard interior

Kelley W King

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Re: Running Hot?
« Reply #11 on: July 22, 2014, 01:46:30 PM »
Harbor Freight sells the IR tool for usually $29.00. One of the best tools I have bought lately. It is as accurate as the $600.00 one we have at work, just does not record or do thermal images. They have many uses.
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Stingr69

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Re: Running Hot?
« Reply #12 on: July 22, 2014, 04:48:01 PM »
The intake manifold ehaust heat passage will still flow some exhaust even if the flapper is removed.  You can block the non-choke stove side of the intake at the passage and the choke will still work from the heat migration in the aluminum but it might be a little slower to pull off.  Not a big deal.  If the passage is blocked on one side, no exhaust gas will travel through inside the intake manifold.

-Mark.

Vince

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Re: Running Hot?
« Reply #13 on: July 29, 2014, 08:45:47 PM »
Well I was finally able to do some checking on the underhood temps.  I drove the Z for between 2-3 miles to get the engine up to temp.  The outside air temp was in the mid 80's.  While driving the temp gauge stayed right around the first quarter marking, maybe one mark up toward the half marking.  While idling in my driveway the gauge read right at the one half marking.  The engine would not hold a steady idle but slowly had the idle decrease until the engine died.  This happened 3-4 times.  While the engine was not running the temp gauge would increase until it was between the one half marking and the three quarter marking.  This I take to be normal due to heat soak. 
Here are the temps I recorded with an infrared gun: 

radiator hose at thermostat- 183, bottom radiator hose- 164
exhaust manifold left hand side (driver's) from front to back- 364, 455, 417
exhaust manifold right hand (passenger) side again from front to back- 433, 570, 562
intake manifold at the high rise part on driver's side- 227
radiator across top- 145
radiator across bottom- 99
valve cover driver's side- 164
valve cover passenger side- 194
driver's side head-194, right at the temp sensor was 179
passenger side head- 253

I wasn't able to get accurate readings anywhere else or didn't think of trying anywhere else.  Definitely the right hand side (passenger) of the engine is a lot hotter than the driver's side.  I wasn't able to check other things while taking these temp readings as the engine was too hot to touch.  Any ideas out there?  Thanks again guys for all your help and opinions.  Just to add a side note:  the engine used to be able to idle for extended periods right at 900-1,000 rpm, with the temp gauge reading not much higher than the one quarter marking and without dying.  It also would restart while warm or hot with no problem. 

z28z11

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Re: Running Hot?
« Reply #14 on: July 29, 2014, 10:26:47 PM »
Really does begin to sound more like a flow problem. Flush the system with the best product you can find, change the water pump and the thermostat. Check and/or change the cap - you need to run about 12-15 psi in the system to make it work properly. If no big improvement, I'd take the radiator out and replace with another known used clear radiator, or a cheap repop just to isolate the problem. Or, just core the old one like most of us are having to experience.

What does the coolant look like ? Dark colored, any foam in it ? Leaking head gaskets can cause hot spots/steam pockets like this. Oil clean ? Any coolant contamination ? Hoses collapsing ?

Bad flow across the radiator could also be a culprit, as we conjectured before. Bet the lower half is plugged - that's why the temp is so low in the bottom half.

One other thing - I witnessed a big block Chevelle do this once upon a time - turns out it was spun bearing (main), causing the engine to not only run hot, but choke down and die when it warmed up enough to start galling on the crank. Check your oil pressure with a mechanical gauge, and a mechanical temp gauge if you can. Just to make sure -

Regards, and good luck -
1968 Z28 M21/U17 BRG/W
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06