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tempature spike

Discussion in 'The Hokey Ass Message Board' started by gatordave, May 22, 2011.

  1. gatordave
    Joined: May 28, 2010
    Posts: 57


    I need some help/advice on a regular temp-guage spike.

    First, the back story. I've had my '56 Chevy for 25 years. Engine is a 327, 60-over, 1.94 heads, mild cam. The build on the engine is 20 years old, but very few miles and it runs strong -- no smoke, no oil consumption, etc.

    But the car has always had a problem with overheating when sitting in line. Running at speed, never a problem. Over the years I've gone from stock radiator to a big Griffin; stock blade to electric puller that runs constantly.

    About two years ago I had a lot of work done on the car: AC, serpentine belt system (new water pump); Classic Instruments dash insert (replacing manual temp guage).

    Car ran cool as a cucumber, but after driving 10 miles or so and coming to a halt, the guage goes from 190 to full hot in about 10 seconds. This usually occurs when I get from from a ride, or yesterday when I got to the local cruise night.

    No detonation, no dieseling, no overflow puking, etc. And, when you lift the hood the engine doesn't seem to be throwing off a ton of heat.

    This happened last fall and I switched from a 180-degree to 190-degree thermostat and it seems to cure the problem. I drove the can all winter (on nice days) and never had the problem. Sat in slow traffic a couple of times and the car never got above 200.

    Yesterday it's hot. On the drive to the cruise, the car ran at 190, including a couple of stops at lights. But, once I stopped at the cruise entrance to get a raffle ticket, the guage climbed to full hot. Drove to a spot, stopped. When I shut the engine off there were a few (three or four) little "bump noises". Not dieseling, though.

    Same thing on the way home -- normal temps, but in the time it took to stop outside the garage, back up a little and then pull in, the thing spiked once again. Same little "bump" noises.

    But, underhood seemed fine. No overflow, no hissing or bubbling, no apparent excessive heat.

    Sorry for all the detail, but I've been fighting this gremlin for years and I'm stumped.

    Thanks in advance for any suggestions.
  2. GassersGarage
    Joined: Jul 1, 2007
    Posts: 4,728


    Years ago, I bought a '51 Ford and the seller said it didn't overheat. I trailered it home and took it for a ride. 5 miles and the temp was 215. It didn't puke so I drove it home. I added a pusher fan which helped. Drove to a cruise spot (35 miles) noticed it was leaking from the upper hose. I drove home and replaced the hose, which was too big. The previous owner had sleeved the hose and double clamped it. Since the hose was off, I check the thermostat. No thermostat, so I added a 160 thermostat. I noticed the vacuum advance wasn't hooked up so I added a line. All the above cured the overheating and now she runs at 185. I asked the previous owner how he sat in traffic. He said, "Oh, I didn't sit in traffic because it would overheat". He said he never runs vacuum advance or thermostats.
  3. Ole don
    Joined: Dec 16, 2005
    Posts: 2,915

    Ole don

    Its time to rent a radiator preasure testing outfit. Look for a bad head gasket or a small crack in a head that opens when hot and water flow slows. You seem to have covered several bases.
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 49,261


    What kind of gage, and where is it?

    Did you try the hole in the thermostat trick?

    But yeah, see if there's exhaust in the cooling system.

  5. flamed34
    Joined: Dec 30, 2009
    Posts: 733


    It sounds like everything that could fail has been replaced/checked.
    Since this is a 20 year problem, I wonder if it could be caused by partially blocked water passages? Believe it or not, core sand can sit in gullies forever, or it could have partially collapsed during casting. I work in an engine plant, and occasionally we see similar issues with castings. It could be low flow at idle just in the passage where your temp sensor is located...hence it doesn't seem/act hot. Possible a second sensor would tell the tale.
  6. tommy
    Joined: Mar 3, 2001
    Posts: 14,757

    Member Emeritus

    Yep and don't listen to the ported vacuum advocates. The system has always been designed to run on manifold vacuum until the smog systems started and they wanted over 200 operating degrees. In the 50s 60s it was common to swap from a 180 Thermostat to a 160 in the spring. I never saw 190/195 thermostats until the smog engines.
  7. b-body-bob
    Joined: Apr 23, 2011
    Posts: 509


    Every time I've seen the temp gauge sweep to max then come right back down there's been a blown head gasket involved. I reckon it's an air bubble passing through the system.
  8. gatordave
    Joined: May 28, 2010
    Posts: 57


    The head gasket seems to be the culprit, perhaps.

    One thing that I forgot to mention. This morning I took the cap off the radiator and there was a little -- just a little -- pressure left in the system. That was the case the last time it spiked on the way home.

    That makes me think that perhaps the bad head gasket is pumping exhaust into the cooling system, increasing the pressure.

  9. Sanford&Son
    Joined: Oct 13, 2006
    Posts: 559

    from Visalia,Ca

    Are you running a shroud? mine dropped temp 20 degree's
    Is the radiator cap the right lbs?
    Are the fan blades pulling enough air?

    60 over sometimes can create alot more heat, I am running a 160 thermostat that really helped lower temp sooner than trying to cool engine after opening at 180?
  10. gatordave
    Joined: May 28, 2010
    Posts: 57


    The fan is shrouded and it pulls like a beast, so I don't think that's a problem.

    I am starting to think it's a head gasket. If that tests out OK, I'll try a 160-degree thermostat. That's a cheap, easy change.
  11. 69fury
    Joined: Feb 24, 2009
    Posts: 1,419


    i wouldn't wasted time with a 160* stat. If your cooling system wont keep it at 160*, then all you're doing is starting the process earlier in the day.

    If your cooling system is capable of keeping your mill at 160*, then you'll have trouble with condensation that doesn't boil out of the crankcase as easily (if at all), increased acids and varnishes in the crankcase, bores that don't reach full temp and therefore wear in an out of round pattern that differs from how it's supposed to (poor ring seal), and oil that dies an early death. The cam wont like you much either.

    I'd confirm the vacuum is connected properly, and then look to the head gasket.

  12. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,912

    dirty old man

    Back in the 60s I built a .060 over 327 w/ 12.5:1 TRW pistons. Always had a problem with overheating in a limited sportsman dirt oval car.
    Teardown revealed a split cylinder wall.
    Last edited: May 22, 2011
  13. Weasel
    Joined: Dec 30, 2007
    Posts: 6,693


    While I appreciate that the immediate reaction is that it may be a mechanical/cooling problem, I would suggest that you test it when it spikes by aiming a non contact thermometer (they're cheap at Harbor Freight), to see if it is actually overheating or if you might have an electrical problem - faulty sender, bad ground, faulty gauge. I have a problem with a Classics Instruments gauge that spikes to 260˚ as soon as the engine (SBC) gets to operating temp in traffic - on the Freeway it drops down to 195˚. John Mcleod from Classic Instruments looked at it at a show and after swapping out the sender for a new one, concluded that it was the gauge itself. The fault developed after several years of normal operation.

    John is here on the HAMB under his name is very helpful. You might want to do as I suggest before ripping anything apart chasing a possible phantom....
  14. 69fury
    Joined: Feb 24, 2009
    Posts: 1,419


    just thought of something- how and where is the wiring? You said it's always done this- since temp gauges work on resistance-and resistance increases with heat,- is it possible that you have a resistance issue where a connection is suspect and close to heat?

    That would explain a spike when coming to a stop and losing some airflow underhood especially when you're not actually feeling a bunch of heat coming off the mill...

    I like the previous idea of a temp gun aimed at it before tearing it apart. Also you should experiment a bit- During a spike - pop the hood, have someone hold it at a really high idle or up to maybe 2500 for a few seconds and watch the gauge while you watch under hood for hose suction/ballooning, cap weeping, etc....

  15. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,912

    dirty old man

    This is why I like to use mechanical, direct reading gauges where possible.
  16. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    from Wisconsin

    Do you have the sending unit in the head or the intake? I would check temps with a non-contact thermometer. Check at several different places on the heads, thermostat housing, water pump, radiator inlet and outlet to see if there happens to be a hot spot or if the gauge is accurate.

    I'm wondering if you could be getting some air pushing into the cooling system that the water pump is able to overcome at higher engine speeds. You say you have pressure in the system the following day. Liquids aren't compressible so the coolant volume should shrink when it cools. If you run a recovery tank, the cap will allow atmospheric pressure to push coolant into the radiator. The system pressure will be equal to or less than atmospheric pressure. If you don't run a recovery tank, there shouldn't be any pressure when it's cold unless there is a large amount of air in the system.

    I check for air by putting about a 6 inch long pipe in the heater outlet in the intake manifold with a valve at the top of it. Start the engine and crack the valve until coolant comes out to bleed off the air. As you run the engine, air will find the highest point and fill the pipe with air. Check to see if the pipe fills with air.

    There is a chemical test for compression in the cooling system.
  17. gatordave
    Joined: May 28, 2010
    Posts: 57


    Sending unit is in the intake on the passenger side.

    I'll pick up a new sending unit and a non-contact thermometer to continue troubleshooting.

    Thanks to all for the help.
  18. gatordave
    Joined: May 28, 2010
    Posts: 57


    Well, a month later we're still chasing this. It turns out that that Classic Instruments gauge is accurate. We put in one of their replacement sending units; same behavior. We checked all of the electrical connections, etc., in consultation with Classic; everything is set up properly.

    So we bought a cheap mechanical gauge, installed in in the intake crossover next to the other sending unit. Cheap mechanical gauge mimics the Classic gauge: engine is running hot.

    Did the exhaust-fumes-in-the-coolant test. Negative.

    Engine is definitely heating up. Last couple of times (testing gauges) when we shut it down you could hear some percolating in the system.

    Next step is warming it up and checking the radiator for cool/hot spots, but that doesn't seem likely as it's a Griffin radiator that's only a few years (and very few miles) old.

    Any other thoughts? Thanks.
  19. brad chevy
    Joined: Nov 22, 2009
    Posts: 2,627

    brad chevy

    You also said you changed to the surpentine belt and pulley system.Is the water pump being turned fast enough at idle or not?Got any pics of your setup?
  20. gatordave
    Joined: May 28, 2010
    Posts: 57


    The pulley system is the standard Concept One serpentine belt system.

    We'll check out that possibility, though.

  21. Verified and or eliminated so far:
    Electrical issue
    Mechanical gauge malfunction
    Combustion gases in cooling system
    Mechanical gauge confirms

    However there are no symptoms of the engine running too hot?
    Ok both sending unit and mechanical gauge are in almost the same spot. I'd try a different local and a temp new wire direct to the gauge.
    you hear gurgling and purcalating- indicative of air in the system.
    Does the temp of air from heater core also mimic the gauge?

    At this point I'm still not convinced the motor is running hot because its showing no symptoms of that other than wacky gauge reading.
  22. AG F/C
    Joined: Oct 20, 2009
    Posts: 361

    AG F/C

    Make sure the pump is turning the correct direction. Many serp. belt systems can turn the pump the wrong direction.

    Are you utilizing the bypass? Depending on the stat location the TS closes and all flow stops so even if the engine core gets hot the water around the TS can remain well below. Once it does open the core water flows out and you will see it as a rapid spike in gauge temp.

    As posted already drill 2 3/16 holes in the TS rim. May warm up more slowly but the constant flow past the TS will help stabilize temp spikes.
  23. medicinal_marinara
    Joined: Nov 24, 2009
    Posts: 139

    from Oregon

    Are you using a stiff enough lower radiator hose? Sometimes, when the spring rusts out, the lower radiator hose can collapse under the suction of the water pump, blocking flow.
  24. 69fury
    Joined: Feb 24, 2009
    Posts: 1,419


    that would show most at rpm (highway) instead of at idle.
  25. Truckedup
    Joined: Jul 25, 2006
    Posts: 4,129


    Very off topic Subaru Foresters like to blow head gaskets. Exhaust gases get into the cooling systems,generally there is no external leak.The first obvious sign is sudden temperature spikes.Then you see a brown scum in the overflow tank. Removing the cap and there seems to be excessive pressure...If ignored the radiator can become over pressurized and actually split a seam and or eventual engine destruction.

    You engine probably doesn't have an overflow or coolant recovery tank.Look in the radiator for scum. There's a test for exhaust in the coolant,cost less than a 100 buck to have done. I believe you can buy a do it yourself kit.
  26. DrJ
    Joined: Mar 3, 2001
    Posts: 9,418



    Running with retarded timing will make it overheat.

    Idling without the vacuum advance sourced to manifold vacuum will make it overheat at idle.

    GassersGarage gave you the answer in the first response but so far seems to have been ignored.

    Hook up the vacuum advance to full time manifold vacuum.
    If you don't have Vacuum Advance, trailer the car to the race track.

    Yes, a few Chevy's/Corvettes have been made without vacuum advance.
    They all ran hot at idle too!

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