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Thread: 1968 Skylark 350 operating temp-hot at idle

  1. #1
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    1968 Skylark 350 operating temp-hot at idle

    hi all, i have a 1968 Buick Skylark Custom. 350 4bbl and 2 speed auto. i have just freshened up the engine with new rings and bearings and a small comp cam (268) new water pump, new thermostat (180) new 1 core radiator (plastic tank model from Rock Auto) new 16lb recovery type radiator cap and overflow bottle installed. block was hot tanked- water jackets were full of scale. engine runs the stock fixed fan and has the shroud installed.
    engine performs great and temp sits on 185 while cruising. stopped at lights the temp will come up to 200 but as soon as im on the move it goes back down to 185. i have only just installed the mechanical temp gauge after the engine rebuild (only had the light before) so am unsure if this is normal behaviour for buick engines?

    have checked the engine/ radiator with my heat gun after a run to warm up the engine, engine idling in park, temp gauge reading 195-200 and right on the thermostat housing its reading 204-213, pointing at the gauge sender its right on 195 (so gauge seems to be accurate) radiator inlet 198, radiator outlet, i forgot to write this down, but think it was 164 so am definitely getting flow through the radiator.

    have checked the timing -comp cams recommended 16deg initial, have backed off to 12 but no change to the temp.

    also the trans isnt great - next thing on the job list, but it runs through a separate trans cooler so shouldn't be an issue of transferring heat.

    am wondering if the new radiator i purchased just isnt up to the job? does 160 ish sound like enough temperature differential to keep the engine cool?

    read on another thread (455 overheating) that someone recommended drilling a 1/4 inch hole in the thermostat and to fill the radiator with the engine running to eliminate air bubbles? is this an issue with 350's also?


    thanks in advance.


    Orange

  2. #2
    I would suspect you just don't have enough radiator.
    I usually drill a 1/16" hole in the thermostat, the hole just has to big enough to bleed out air which may become locked under the thermostat. If you buy heavy duty or high flow, they usually already have a hole with a small check valve.


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  3. #3
    a - 200 is not a hugely problematic temp, if you get up over 240 that would be a big concern. 260 should be shut down immediately

    b - fixed fan so clutch can't be an issue. you didn't mention it but i would be shocked if you didn't get this, new radiator hoses, yes? and the hose for outlet side of the radiator has a support spring ( you're going to pull a vacuum on the outlet side of the rad ) on the inside?

    c - the new overflow bottle is single line? if two line, how do you have it plumbed?

    d - get an old set of panty hose and cut off one leg ( no holes in the leg you use ). pull the hose off of the inlet side of the radiator, drop the panty hose leg, toe first, into the inlet side of the rad, wrapping the top of the leg back over the inlet nipple to keep it from falling into the rad. re-attach the inlet hose, securing the top of the panty leg.

    this forms a trash trap, after running the car for a week or so you should pull the panty hose out of the radiator and see what trash you've picked up in the toe of the panty leg.

    you would hope that the hot tanking got the block clean and ... didn't simply knock a bunch of scale loose but didn't get it out. if you've got trash in the panty hose there is probably a BUNCH clogging up the new radiator ...
    The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
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    Quote Originally Posted by Bob View Post
    I would suspect you just don't have enough radiator.
    I usually drill a 1/16" hole in the thermostat, the hole just has to big enough to bleed out air which may become locked under the thermostat. If you buy heavy duty or high flow, they usually already have a hole with a small check valve.

    Hi Bob,

    thanks for your reply

    checked the Thermostat and it does have the jiggle pin, bench tested it and opening temp is withing a couple of degress of what it should be so guessing that's all good

    am looking at another possibility..... the carb. with the temp only rising at idle, could be running too lean on the idle circuit. have tried richening up but this POS (fully recond 650 spread bore double pumper) isnt playing ball. Have a mate dropping me off his carb to try on it to hopefully prove or eliminate a lean idle as the cause


    if the carb idea doesn't sort it out, guessing your suggestion of a larger radiator might be the go - looking at an ADPI/Pro # 8010348 from Rock Auto unless someone can suggest a better (but still affordable) option

    Regards,


    Orange

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    Quote Originally Posted by bob k. mando View Post
    a - 200 is not a hugely problematic temp, if you get up over 240 that would be a big concern. 260 should be shut down immediately

    b - fixed fan so clutch can't be an issue. you didn't mention it but i would be shocked if you didn't get this, new radiator hoses, yes? and the hose for outlet side of the radiator has a support spring ( you're going to pull a vacuum on the outlet side of the rad ) on the inside?

    c - the new overflow bottle is single line? if two line, how do you have it plumbed?

    d - get an old set of panty hose and cut off one leg ( no holes in the leg you use ). pull the hose off of the inlet side of the radiator, drop the panty hose leg, toe first, into the inlet side of the rad, wrapping the top of the leg back over the inlet nipple to keep it from falling into the rad. re-attach the inlet hose, securing the top of the panty leg.

    this forms a trash trap, after running the car for a week or so you should pull the panty hose out of the radiator and see what trash you've picked up in the toe of the panty leg.

    you would hope that the hot tanking got the block clean and ... didn't simply knock a bunch of scale loose but didn't get it out. if you've got trash in the panty hose there is probably a BUNCH clogging up the new radiator ...


    Hi Bob,

    thanks for your reply, didnt think 200 was going to cause any real engine issues, just never had an engine that behaved like this + summer still hasn't arrived here so just wanted to sort before it warms up here.

    yes sorry both top and bottom hoses are new and the bottom has a spring

    overflow bottle is a 2 line. it has the hose from the radiator neck into the overflow bottle (protruding almost right to the bottom so always submerged in coolant/water) + has a 2nd hose (overflow) in the bottle that only protrudes an inch into the bottle (does not sit into the coolant/water)

    guy at my radiator shop suggested your stocking idea, have done that and is crystal clear

    am looking into the carb (see above post) fingers crossed this gives some clear answers


    Regards,


    Orange

  6. #6
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    If this is a freshly rebuilt engine, maybe it is just real tight (friction=heat). Take her on some long trips, get 500 miles on the engine, get her broke in, your heating problem might cure itself.

  7. #7
    overflow bottle is a 2 line. it has the hose from the radiator neck into the overflow bottle (protruding almost right to the bottom so always submerged in coolant/water) + has a 2nd hose (overflow) in the bottle that only protrudes an inch into the bottle (does not sit into the coolant/water)


    okay, i doubt this is the problem, especially with the one hose being plumbed to the rad neck and the likely narrow diameter hoses you're probably running BUT

    ...

    i have seen a 2 line bottle be a problem before, due to the way it was plumbed.

    in the problem installation, it was a fancy dancy aluminum bottle with ~1" ID nipples on a race car. one of the 1" lines was T'd into the upper rad hose and the other 1" line was plumbed into the bottom rad hose.

    this car had had new radiators installed, new water pumps, a new head gasket ( 4 cyl Ford in a Ministock ), new hoses, etc. the engine builder had looked at it, people with 20 years in racing had looked at it, nobody could figure out why that thing ran hot.

    then i asked, "Isn't the radiator a flow restriction?" ( in electrical terms, a resistor ) upon being told that, yes, the radiator probably was a flow restriction i asked the follow up question, "Isn't the overflow bottle plumbed as a radiator bypass? ( in electrical terms, a parallel circuit of nearly zero resistance )"

    we fixed the plumbing so that both sides of the overflow bottle were T'd into the vacuum hose on the outlet side of the radiator and the engine never over heated again.


    i'm assuming the rad neck would, in pressure terms, be nearly the same as the inlet hose. depending on where your 2nd hose is plumbed too, that "bypass" scenario may or may not be an issue. either way, i would be surprised if the ~1/4" line plumbed to the rad neck could flow enough water to make a real difference.
    The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
    Vladimir Lenin

    Government schooling is about "the perfect organization of the hive."
    H.H. Goddard, Human Efficiency (1920)

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    problem solved

    Hi All,

    Tried a different carb and although it didn't fix the overheating at idle, it made the car run a hell of a lot smoother and more responsive. moved on to checking air flow. car was running the OE shroud and fixed fan but there never seemed to be a lot of air flow. had a viscous fan off a 1970 skylark in my parts collection, so bolted that on, OMG these things draw some air! took the car for a good run to build up some heat, I did some start-stop tests and crawling along at slow speed, temp sat between 180~185! looks like the problems finally all sorted, am guessing the 'stock' fan just wasn't up to the task with the higher compression/cam etc

    thank's for your replies, time to fill the tank with some over priced go go juice and get cruisin

  9. #9
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    i have just freshened up the engine with new rings and bearings and a small comp cam (268) new water pump, new thermostat (180) new 1 core radiator (plastic tank model from Rock Auto) new 16lb recovery type radiator cap and overflow bottle installed. block was hot tanked- water jackets were full of scale. engine runs the stock fixed fan and has the shroud installed.
    You just "overhauled" the motor! It is going to be TIGHT and produce more friction! I did this just recently and I was running consistently at 228 degrees at highway speeds, at idle in traffic etc (at it's worst). After 7K miles, it is running 185-190 consistently with the A/C full on and the temp in AZ at 110 degrees outside ambient air temp!

    Get a couple thousand miles on it before you start really getting worried over it.

  10. #10
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    overheating (or heat creep) at idle usually means either not enough airflow over the cores or the radiator is too small, or waterpump (though not as likely). You can confirm this if you drive and it cools down and stays cool, then the issue is either fan or too small of a radiator. If it stays cool at idle, and overheats at speed, that can be restrictions blocking the airflow through the radiator, timing, carb tuning (ie: lean condition), etc.

    If you end up needing a new radiator, we make aluminum versions here:
    https://www.teambuick.com/forums/sho...tion-Radiators

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