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Technical SBC over heating

Discussion in 'The Hokey Ass Message Board' started by heritic88, Dec 12, 2020.

  1. heritic88
    Joined: Sep 7, 2008
    Posts: 116

    heritic88
    Member

    Hey guys and gals I’m having a hair tapering issue that I can’t seem to lick. I rebuilt my engine over the last couple of years (just a mild built 305 maybe 300hp). It had an aluminum radiator before the rebuild that worked great but I needed to replace because it got a hole some how dead center or the core. So I replaced it with another 3 row aluminum radiator no leaks. I drove it for 30 minutes to my buddies shop to put exhaust on it and it was over heating like crazy. So I figure I have a bubble or something, I let it run for awhile either the cap off and that seems to fix it. I proceed to chase this thing overheating, I put stainless upper and lower hoses to try and class it up a bit. I would not recommend this, I had a hose pop off so I double clamped it. I then blew a hole in the hose. I replaced with some good old fashioned rubber radiator hoses and it seemed fine until I left it running for 15-20 minutes to let the battery charge and it is steaming like crazy and is leaking from the thermostat housing now. I’m getting out of ideas besides finding a cliff somewhere. Any suggestions would be appreciated.


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  2. Mr48chev
    Joined: Dec 28, 2007
    Posts: 29,058

    Mr48chev
    ALLIANCE MEMBER

    Exactly how is it overheating? Gage shows higher than you think it shoud? Pukes coolant on the ground? Or?????

    Second question is how hot is overheating by your standards?

    Steaming from the thermostat housing probably means that you have a flawed thermostat housing especially if it is one of those chrome ones from the parts house or the gasket isn't sealing right.
     
  3. Stuck Thermostat?......can happen anytime. Check,and see if water is circulating at operating temp.Leave the cap off,and run it awhile,and look to see if its flowing.I do the old spit in it,and see if it moves trick.If its swept away you have flow.If it just sits there replace the stat.
     
    Elcohaulic likes this.
  4. DDDenny
    Joined: Feb 6, 2015
    Posts: 14,835

    DDDenny
    Member
    from oregon

    Run that by me again!
     
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  5. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 6,695

    56sedandelivery
    ALLIANCE MEMBER

    Stuck or upside down thermostat? Had a good running 327 in a Nova some time back, and it all of a sudden started to overheat. I looked at everything, thermostat, water-pump, hoses, even the radiator. It turned out to have broken one of the two mechanical advance springs in the distributor, and was running too far advanced all the time; it was occasionally hard to start that I attributed to overheating. I even got stopped on the freeway trying to "blow it out" by a Washington State Trooper, who I knew through the hospital I worked at in the E.R.; he did't site me, just told me to get out of there, and to not do it again. This trooper had a V-8 Vega as one of his personal cars, so he was a hot rodder. Just a little, tiny, spring, and I chased that overheating for several days before I found it.
    I am Butch/56sedandelivery.
     
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  6. Fresh build, Wrong year water pump running backwards? Also as Butch stated check the weights in the dizzy, I had same thing happen to me on a OT car That I had put together, Got hot and chased it forever it also had stuck weights.. Bad/cheap thermostat also.
     
    mad mikey likes this.
  7. If it’s blowing hoses off there’s obviously way too much pressure in there. That kind of pressure comes from combustion gases being forced into the cooling system.
    Simply watch in the radiator fill hole for an endless stream of bubbles. If so there’s other ways to confirm. Leaving the cap off is a big clue.

    305 heads are notorious for cracking.
     
    BJR, anothercarguy, jimmy six and 3 others like this.
  8. ^^^and that could have been what blew out the first radiator^^^^^
     
    egads, mad mikey and Desoto291Hemi like this.
  9. That's what I am thinking , cracked head, blown head gasket , etc. Pressure in cooling system and combustion gasses .
     
  10. Bob Lowry
    Joined: Jan 19, 2020
    Posts: 572

    Bob Lowry

    I had a sbc that did the same thing..turned out the brand new thermostat would not open.
    Removed it and the engine ran nice and cool. Put the themostat in a pot of boiling water
    on the stove and it never did open. Think simple and work your way backwards to solve it.
     
  11. heritic88
    Joined: Sep 7, 2008
    Posts: 116

    heritic88
    Member

    Tha is guys I’ll definitely pull the cap and check the distributor. I need to pull the thermostat and through it in some boiling water. They are brand new vortec heads, I checked the oil last night and didn’t have any signs of milkshake. The distributor cap and thermostat are new too so who knows.


    Sent from my iPhone using H.A.M.B.
     
  12. jackandeuces
    Joined: Feb 20, 2006
    Posts: 1,004

    jackandeuces
    Member

    Do you have a vacuum advance distrubtor, if so are you hooked to ported or unported vacuum??here a though...
    This was written by a former GM engineer as a response to a similar question:As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense, and as a result, a lot of folks are under the misunderstanding that vacuum advance somehow compromises performance. Nothing could be further from the truth. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. I have this as a Word document if anyone wants it sent to them - I've cut-and-pasted it here; it's long, but hopefully it's also informative.

    TIMING AND VACUUM ADVANCE 101

    The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

    The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

    At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

    When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

    The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

    Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

    If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

    What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

    Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren't fully-deployed until they see about 15 Hg. Manifold vacuum, so those cans don't work very well on a modified engine; with less than 15 Hg. at a rough idle, the stock can will dither in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15 Hg. of vacuum at idle need a vacuum advance can that's fully-deployed at least 1in, preferably 2 in of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8 in of vacuum, so there is no variation in idle timing even with a stout cam.

    For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it
     
    Last edited: Dec 13, 2020
  13. HemiRambler
    Joined: Aug 26, 2005
    Posts: 4,207

    HemiRambler
    Member

    Don't rule anything out because parts are "new" - -- New just means untested. I agree with the guys saying start with basics. Ensure FLOW thru the thermostat, radiator and hoses (does the lower have a wire inside?). Used radiator could also be partially blocked - check the core for cold spots too. I had an issue where it'd idle all day and be fine around town then overheat on the freeway - reason radiator was too small. Next I put in a bigger radiator and I reversed my problem - I'd overheat around town but was fine on the freeway. Solved that with a fan shroud. It's almost always the basics. Good luck in your trouble shooting.
     
  14. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,210

    jaw22w
    Member
    from Indiana

    I remember reading this several years ago. Probably the best write-up on vacuum advance I've seen. I know it helped me. SBC guys should all read and absorb this information.
     
    harpo1313 likes this.
  15. jimmy six
    Joined: Mar 21, 2006
    Posts: 9,004

    jimmy six
    Member

    I’ve never put in a thermostat without the boiling water test. As for ported vs manifold vacuum we just finished a warmed up GMC 302 6 with a Tom Langdon HEI and were told to use manifold vacuum only. We had a tough time idling under 800 rpm and had to shift into 1st on slow down corners. After a month I decided to try ported which was pretty much a pain as I had hard lined a lot. It was a new car. Idled at 600, ez 2nd gear corners with no bucking or surging. 10 degrees at idle 37 at 2500 with vacuum line plugged. 170* at idle 160* in moving traffic.
    The best thing to do to check cooling is to have the cap off, water 1” low and look for water movement at idle after water is hot enough for the thermostat is open. You need movement at idle.
     
  16. Since you have Vortex heads I trust you do have a manifold with a by pass hose set up.The early blocks/ heads have a hole in the block on the passenger side that line up.When you go Vortex that disappears but its fine with the by pass hose manifold.If you failed to hook that up you could run hot.
     
  17. Greenbullitt
    Joined: Dec 11, 2020
    Posts: 3

    Greenbullitt

    not a bad observation. you can get a block test kit at napa to check for combustion gasses as well
     
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  18. Jalopy Joker
    Joined: Sep 3, 2006
    Posts: 26,623

    Jalopy Joker
    Member

    - Edelbrock carburetor instructions support this too - but, had a factory crate ZZ4 350/355 HP (included distributor and manifold) ran best with no distrib vacuum
     
    Last edited: Dec 13, 2020
    jackandeuces likes this.
  19. Other than the quoted paragraph which is BS; That is a very good article explaining distributor advance operation....
    It always takes some experimentation to figure out what your engine likes best.
     
  20. Tickety Boo
    Joined: Feb 2, 2015
    Posts: 1,331

    Tickety Boo
    Member
    from Wisconsin

    Do you know your compression ratio with the new 64 cc Vortec heads ? Might need premium gas

    When I built a 0 decked flat top piston 355 the compression went up to 10.27 using the new Vortec heads the old heads were 76 cc.
    Got away with running 91 octane gas because of the extreme energy Comp cam
    If going to run hard I mix in some race gas or add octane boost.
    Had a overheating problem driving 200 miles north one time at Land O Lakes WI, filled her up with 91 octane and about 1/4 mile down the road the temp gauge started to clime :eek: put in a can of octane boost and it helped o_Oso the 2nd can got it back to normal, the funny thing was it wasn't pinging and never had that problem again :confused:
    My best S.W.A.G. is that they sold me 87 at the 91 pump, I always carry some octane boost along now.
     
  21. Mr48chev
    Joined: Dec 28, 2007
    Posts: 29,058

    Mr48chev
    ALLIANCE MEMBER

    The water pump thing is big when switching small block parts around, What belt setup do you have?
    V belts require a water pump that turns clockwise looking at it from the front. If you put V belts on the 305 with a water pump intended for a serpentine belt setup you would be turning the pump backwards as pumps with serpentine belts run counter clockwise First time I ran into that a guy bought a rather ragged early 82 or 3's third gen Camaro that someone had stuck a mid 60's 327 in that had V belt drive on it. When they replaced the water pump they bought a pump for the 80 something Camaro rather than the 60 something engine. The engine did exactly what you are describing, heated up going down the road but didn't overheat at an idle as the backwards facing fins in the pump could move enough coolant at an idle but not at road speed.

    Still Timing is critical, late timing will cause an engine to run hot. The above mentioned coolant passages in the heads and intake thing is something to check if you have an aftermarket or older intake on it.
     
  22. heritic88
    Joined: Sep 7, 2008
    Posts: 116

    heritic88
    Member

    Haha autocorrect it was supposed to be hair tearing I just have fat thumbs.


    Sent from my iPhone using H.A.M.B.
     
  23. heritic88
    Joined: Sep 7, 2008
    Posts: 116

    heritic88
    Member

    Good call I’m going to pull it out this week and through it in some boiling water when my wife’s at work. Seems safer that way.


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  24. heritic88
    Joined: Sep 7, 2008
    Posts: 116

    heritic88
    Member

    Over heating meaning pegging the temp gauge. It made a pin hole in the silicone around the housing. I’m going to pull I all off again and see if the thermostat is stuck. The upper hose get warm like coolant was flowing but who knows.


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  25. heritic88
    Joined: Sep 7, 2008
    Posts: 116

    heritic88
    Member

    I think the heads are good, I swapped in some brand new vortec heads.


    Sent from my iPhone using H.A.M.B.
     
  26. heritic88
    Joined: Sep 7, 2008
    Posts: 116

    heritic88
    Member

    Dang that’s a lot of info, and yes I have a vacuum advance hei distributor.


    Sent from my iPhone using H.A.M.B.
     
  27. heritic88
    Joined: Sep 7, 2008
    Posts: 116

    heritic88
    Member

    Not sure on the compression I need to do some maths. As Ace Ventura says it’s a high performance machine I need to fill it with premium, so that’s all that goes in there.


    Sent from my iPhone using H.A.M.B.
     
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  28. getow
    Joined: May 9, 2016
    Posts: 295

    getow
    Member

    Depending on where you live. If you have an old school garage nearby, and they have a old pre 96 emission machine with a tailpipe probe. You can easily check for hydrocarbons in the cooling system. That would definitely poke you in da right direction. Like, headgasket, cracked head, bla, bla. If none are present, circulation issue is da culprit.
     
  29. heritic88
    Joined: Sep 7, 2008
    Posts: 116

    heritic88
    Member

    This may be a stupid question, the aluminum radiator came with a 1.1 cap which I believe is a 16# cap. Should I look into a different cap?


    Sent from my iPhone using H.A.M.B.
     
  30. iagsxr
    Joined: Aug 26, 2008
    Posts: 141

    iagsxr
    Member

    I'd test the cap just as a matter of course.

    It should have popped the cap long before it blew a hose off or caused the thermostat housing to leak.
     

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