Intake Manifold Getting Very Hot

Discussion in 'Gen 1 & 2 - Engine, Exhaust, Drive Line & AC syste' started by haydenm315, May 7, 2003.

  1. haydenm315

    haydenm315 SHO Member

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    I finished putting my car back together today and drove it for no more than 10 minutes. The crappy inside temperature gauge read a comfortable number, however the manifold was too hot to touch. Acceleration was good but the car seemed to be lacking low end. I just found out that I forgot to plug in the plug that controls the secondaries. Will this cause my manifold to get hotter than it should? I also noticed that I could remove my radiator cap and there wasn't any pressure in there. I did let it cool for atleast 10 minutes before opening up the cap. How long should there be pressure in there?
     
  2. SolidState

    SolidState No Mo SHO

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    I noticed that when my car is moving, or immediately after (!) the manifold is cool to the touch.

    However, leave it sit for a while and it heats up nice. I am guessing that this is because no cool, fresh air is flowing through it, around it and the heat fromt he engine is rising...
     
  3. Machspeed

    Machspeed Infiniti I30t

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    Im assuming having the secondaries closed would restrict airflow there fore making your manifold hotter. Even when your secondaries are open your intake gets pretty hot normally. As for your radiator cap, there should be pressure for at least 30 minutes. I remeber opening my cap after 2 hours and there was pressure.
     
  4. haydenm315

    haydenm315 SHO Member

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    I'm a little concerned about the lack of pressure. Maybe I've got a minor leak somewhere, though I didn't notice a loss of coolant before taking it apart this time. If the plug for the secondaries is not plugged in, do the butterfly valves stay open or do they close?
     
  5. rendyx

    rendyx SHO Member

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    Open, so I don't think that would cause it. I'd check the coolant hoses to the intake and make sure they are okay. Good luck!
     
  6. shojuan

    shojuan SHO Member

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    My intake gets very hot after driving and it has always been like that. When the car was new the intake got hot. Yeah sometimes I think that maybe my intake gets hotter than it should. But I'm sure it's OK. If I ever get pissed enough about it I'll just get some phenolic intake spacers and a machined intake manifold from Josh at SHONUT Performance. Hot intake means it's acting as a good heatsink though! :D

    Re: the pressure in the cooling system hoses. Not just the SHO but with other cars I've noticed a variety of behaviors. Sometimes it will hold pressure for a good length of time, sometimes it won't. Of course a leak in the system will cause the pressure to drop quickly, but assuming you have no leaks there are several variables at work hear. The most important is how much heat flow do you have between the coolant and the metals the coolant is exposed to. With scaled up cooling passages in the heads heat flow will be relatively slow. With nice clean, scale free passages the heat flow will be much greater. A hot intake suggests to me good heat flow from the coolant to the metals. I know it might be counter-intuitive but assuming you don't have any leaks the behavior you're describing might just be an indicator that your cooling system is in good health. You are right for being concerned. It's a wake up call to check for leaks:
    • <font size="2" face="Verdana, Helvetica, sans-serif">Is the coolant in the recovery bottle getting lower by any noticible amount day to day?
    • <font size="2" face="Verdana, Helvetica, sans-serif">If the recovery bottle doesn't change did you check to make sure the radiator is full when the car is cold? You shouldn't have any air space in there.
    • <font size="2" face="Verdana, Helvetica, sans-serif">Is your cap in good shape even if the other stuff checks out? If in doubt get a new cap. They're cheap.
    <font size="2" face="Verdana, Helvetica, sans-serif">If those things check out and you're not running coolant that is more than a couple years old then relax. Your cooling system is probably in good health.
     
  7. haydenm315

    haydenm315 SHO Member

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    I believe more coolant than I thought leaked out when I took the manifold off to do some work. THe level kept dropping slowly with the radiator cap off with the car off. I kept filling it and it seems to hold pressure now and the manifold doesn't get as hot. The plenums get warm but the runners are still getting hot. I believe this is normal though. My loss of down low power was most definately the unplugged secondary line. All seems cool now.
     
  8. haydenm315

    haydenm315 SHO Member

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    I feel better now, though it seems cooler now that the coolant level has evened out and I plugged the thing in the allows the secondaries to function correctly. Thanks for the info. Sometimes I get senile and think things were different before I messed with it.

    As you should know from my sig, I've put some time into making the motor work harder with the stage II cams, ud pullies, and the ypipe. When I did this, I was sure to do a very thorough cooling system flush with a seperate heater core flush as per the helms manual instructions. This seemed to make my car run a bit cooler. THere is still some scaley stuff visible at the neck of my radiator, but I did my best to clean the system out. I think it's working just fine for now. Maybe a new radiator is in store a year or so down the road.


    My father's favorite saying when I was a kid.... "get your head out of your ass!!!!" Constant grilling like this has caused me to become more alert of my surroundings and responsibilities. I'm very responsible when it comes to maintaining cars and detecting problems. I can attribute some of this to him, some to shoforum, and some to my love of cars.
    It has always remained fairly consistent.

    Every morning before I set off on whatever the day holds, I check oil and the level in the radiator. It's never been low, with the exception of today after I put everything back together. I topped it off a few times and it kept dropping a tiny bit. I think it may just be air though. I'm about to go out again. I'll make sure to check it. thumb

    The coolant cap was a low blow to me. I just read and saw on tv recently that it should be replaced every 2 years? I've never replaced my cap. It's probably a good idea to do so. Who knows what the previous owner did.

    [quote
    If those things check out and you're not running coolant that is more than a couple years old then relax. Your cooling system is probably in good health.[/QUOTE]

    I think my cooling system is ok. On a hot day, if I'm sitting still for a while and am doing city driving, the gauge will get up to the bottom of the O in normal before the fan turns on. The gauge temperature level drops fairly quickly and the fan shuts off in maybe 30 seconds. If I'm driving at a moderate pace or on the highway, the needle will sit around or slightly below the M in normal. Where the gauge on the cluster sits is usually not a good indicator due to accuracy discrepencies. I've been meaning to get an aftermarket gauge cluster soon. I want oil pressure, exhaust temperature, oil temperature, and/or water temperature. Do you recommend any gauge sets?
     
  9. sdpatt

    sdpatt Sr. SHO Engr.

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    There will always be a certain amount of thermal energy (heat) that is conducted from the very hot heads up through the intake runners that are solidly bolted to the heads with a metal, heat transferring gasket. While the engine is running and cool air is being drawn in to feed the cylnders and flow over the external surfaces of the intake manifold, the plenum chambers will usually stay quite cool, but never cooler than ambient air temperature.

    After the hot engine is shut down, a significant amount of thermal energy is conducted through the runners and additional heat is convected up from the hot block and exhaust manifolds to cook everything under the hood as the engine tries to dissipate its heat. This is usually called "heat soak" and takes a great deal of heat transfer to resolve.

    If you start a cold engine and drive on the highway where a constant supply of fresh air is supplied to the intake path and under the hood, the intake will be comfortably cool to the touch if you quickly pull over and lift the hood. Let the car idle for a few minutes and the intake will most likely become too hot to touch.

    If the cooling system was not liquid solid, the pressure may be reduced more rapidly than expected due to the contraction of the vapor space. Another possibility is that the extra pressure from the cooling system due to the heat soak after engine shut down caused the radiator cap to do its job and vent the expanding fluid to the expansion bottle. It is not until the coolant lowers its heat and contracts sufficiently to create a vacuum that the coolant will be again drawn back into the system from the expansion bottle.

    Unless you see fluid on the ground, your cooling system is doing just what physics tells it to do. Relax.
     
  10. haydenm315

    haydenm315 SHO Member

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    Thanks scott. I'm now resting easy.
     
  11. Bluto

    Bluto SHO Member

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    What would you guys think of a CO2 discharge that can lower the intake temp to -75* F?

    This is just a brain far..storm.

    I ran across a intercooler cooler, that could actualy work on our intakes. The CO2 would be discharged onto the intake, not in it.
     
  12. 93EmeraldMTX

    93EmeraldMTX SHO Member

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    usually the only part of my intake that is warm at all after i drive it is the runners, the rest is cool to the touch, unless it has been idling for an extended period or been shut off for a while.
     
  13. sdpatt

    sdpatt Sr. SHO Engr.

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    Temperatures to that extreme would cause tremendous thermal stresses on the intake and heads due to the temperature difference between the 200+F heads and the -75F intake. You could actually crack the metal from these stresses.
     
  14. Bluto

    Bluto SHO Member

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    Thanks for the voice of reason scott.

    It would certainly cool down the air in the runners.

    They do put this on aluminum intercoolers, but they don't have the same structural stress.
     

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