Running hot

[rcsteuer]

I have a '49 - 3A that was rebuilt 2 years ago (less than 2,500 mi.) and always runs hot.  I've swapped the thermostat out from a 180 to a 160 and have tried the thermostat with and without the drilled holes. The change from the 180 to 160 brought the temp lower but still not where things should be running.

the issue is that under 35 mph, everything runs at around 175 - 180, but as soon as speed is increased or if there's a long hill, temps will hit 190 -195.  Although it never overheats to the point of blowing off steam, there are side-effects.  After running at those temps, shutting off the vehicle results in the temp jumping to 220 - 225, which causes the radiator to spit water out of the overflow tube - not a lot, but always. While it will start when it's been overheated, it's always harder than a cold start or when it remains below the 180 level.

I've futzed around with timing using tach, dwell and vacuum, as there are no marks on these.  Dwell is 40, tach 670, vacuum 20.

Any suggestions?  I've tried every trick in the book I know of. Maybe someone has a different book?

Thanks

PS radiator cap is new 4lb.

[scoutpilot]

How much over-bore?

[rcsteuer]

.060

[scoutpilot]

That is your problem. Throughout the production lifetime of these blocks, some wound up with thin to begin with cylinder walls. Boring out to 60-over only diminishes the ability of the iron to transfer heat effectively. For this reason, I advise all owners doing rebuilds to sleeve them back to standard.

[rcsteuer]

Hmmm, interesting.  I worked in an automotive machine shop for years where we rebuilt engines, including a number of L4-134s (only shop within 150 mi. that could pour babbit bearings and line bore), and never ran into an issue.  It's been too long (over 40 years) since then, so don't recall original wall thicknesses.  Not suggesting you're wrong, just an observation.

So, if that's the case - where it's a matter of poor transference of heat - have you had any experience with running a larger radiator and/or flex fan, which should provide a bit of relief. If you can transfer heat out of the radiator, it should run a bit cooler. 

Maybe someday, I'll drop the pan and mic the walls, just for the helluvit.

Thanks for your comments

[Rus Curtis]

Assumptions follow:

IF your coolant is mixed properly, you should not boil over.  IF your radiator cap is holding pressure, you should not boil over.  IF you aren't leaking fluid, you shouldn't boil over. 

You didn't state the condition of the radiator.  Has it been cleaned/rodded to ensure no blockage?  Is there belt slippage on the pump (impellers intact)?  Bottom hose collapsing or restricted?

I "think" that if you're cooling at idle/low speed but at higher rpms you experience overheat my mind goes to circulation restriction.  I could be wrong (happens a lot) and Scoutpilot is on to something I know little about.

I had a brand-new thermostat out of the box, stick on me.  Testing in a bowl with a thermometer confirmed it.  It seems your problem still exists even with a cooler thermostat (which makes me think circulation).

[scoutpilot]

What mixture of coolant are you using? Synthetic? Are you allowing the motor to cool for a minute before shutdown?

[rcsteuer]

I know this is an older thread I haven't updated due to being out of commission for a while.  Warmer weather returning to the Northeast has allowed the CJ out of the barn.

Still same issues and I'll (finally) respond/answer prior questions. all of the following done during the rebuild before the jeep was ever run after rebuilding:

  1. The radiator was boiled and flow-tested before installing
  2. Two different 160-degree thermostats with the bleeder hole drilled. Both tested before install and opened at 160.
  3. Antifreeze is ethylene glycol based Prestone, mixed at 50/50.
  4. New 4# cap
  5. New water pump
  6. No sign of the lower hose collapsing

There are actually 2 things that I conflated into a single problem:

  7. After running the Jeep to normal running temps (<180) and parking, the temp increases while parked and the cap will release fluid as soon as the temp reaches approx. 220.
  8. When driving uphill for more than 5 - 10 minutes, temp will approach 200 and engine starts pinging.  Stopping for a minute, brings temp down so that pinging stops and power returns to normal.

What's been done to try to correct overflow at rest:

  9. Changed out cap. to the 2nd 4# cap to be sure it wasn't a cap issue.
10. Adjusted timing by retarding slightly (without timing marks, it's a crap shoot). I've been on both sides of optimal running - either too much pinging or too little power.  As it sits now, the power is excellent until the hill issue pops up. Dwell at 39, tach at 670, vacuum steady at 20
11. Added the shroud to the radiator, which helped somewhat, but did not resolve the issue.

Because the cap releases when parked, I've just ordered a 7# cap. While reluctant to put a 7# cap on, I'm hoping to see if it prevents the overflow, figuring the loss of fluid may be contributing to the overheating.

ScoutPilot - if you're still monitoring - running an engine lean could contribute but I'm not seeing any indication of running lean. If anything, it's probaby running a tad on the rich side.

Any comments are greatly appreciated.

[48willys]

Mine seems to be running a little better temperature after I replaced the thermostat retainer.
The new one was longer and sits against the head instead of relying on a friction fit like the old one.
The only logical explanation I can come up with is the old retainer was allowing coolant around the thermostat and circulating so quickly the radiator couldn’t cool it fast enough.
It wasn’t the cure because the temperature still climbs when pulling long hills, but it did seem to help to some extent.

[scoutpilot]

The pinging under load indicates a too-lean or too far advanced timing condition. What fuel are you burning?

[Rus Curtis]

Trying to decipher this latest post, I'm leaning towards timing.

Your 3A is early.  According to what I've read, there's a timing inspection hole at the back to see the timing marks on the flywheel.

https://cj3apage.com/Forum/index.php?topic=3432.msg28720#msg28720

Some have added a bolt on timing mark that will at least give you marks up front.  This bolt on timing mark will need a notched pulley so that you can measure.

I initially had no idea you were running without a shroud.  Good that you've got it on now.  And YES, multiple seemingly irrelevant details can compound a problem.

[rcsteuer]

Thanks for the replies:

Scoutpilot - running 87 octane.  I bring timing to highest, smooth-running point, then retard about 100 rpm, and adjust idle to ~670. Vacuum is steady at 20.  I've pulled plugs and, while not full of carbon, are definitely on the darker side, so I've been assuming it's running a tad rich, if anything. I rebuilt the carb and even took it apart a second time to verify the metering rod settings, etc. It starts fine cold and when it's warm but hasn't heated over 200.  When hot, it can be stubborn. Under those conditions, where the engine has been heated, harder starting may be an issue of vapor lock (?).

Russ, yes, very early - in fact, I've found a few items that were left over from the 49-2A. Rear end is a Dana 41, not a 44.  The original engine rear plate was replaced but the plate that's on it does not have the timing hole, so it's a crap shoot.  The crankshaft pulley didn't have a timing mark, so when i was reassembling the engine, I brought the engine to TDC and notched a mark as close as I could to the 0° mark on the timing cover.  Not perfect, but it gave me a ballpark reference point.

Any other suggstions are welcome.

[SteveKfl]

All interesting.  Since you say specific degree ranges, I'm "guessing" you're using an auxiliary temp gauge of some kind.  Dare I ask "where" that temp-sensing is done, and is it internal, or "external temps" via a "digital Lazer gun" aimed at locations on the block or head?  Using a gun, I've seen temps of cylinders on top of head vary drastically up to 30 degrees... like #1 @ 173, #2 @ 183, #3 @ 203 (Note: factory temp sensor location under that part of the head), and #4 @ 190.  Those temps were taken with a 180 degree therm warmed up to "operating temp".  Has anyone else done "head surface temps" and gotten similar results?  Could the "perceived temp numbers" be throwing a curve to where your problem is???
 
As a suggested "bandaid"... an added "temp activated electric fan" could boost the cooling as "needed" when "temp activated", like at "rest" when "parked", or under heavy heat load conditions... cheaper than a new block.  Good Luck! 

[rcsteuer]

Thanks for the reply, SteveKfl. Using the analog temp gage that has the sensor mounted directly in a port on the head.  While the absolute numbers may not be perfectly accurate, the differential is what's concerning and causing the problem.  While driving at 40 mph on relatively flat roads, the temp will range from 165 - 180.  As soon as I hit a hill > 1/2 mi, the temp will rise to >195 and it starts pinging.

As a test today, I retarded the timing so that the vacuum was just starting to fluctuate a bit and set the idle screw a bit richer to try to help with running at idle after heating up.  Took it out for a spin and no difference.

I found a spacer that was made to move the fan blade closer to the radiator.  Going to give that a try. 

[Rus Curtis]

From what I have read about cooling, the fan is primary when low speed and idle - as there isn't enough airflow to adequately cool the fluid.  At speeds roughly above 35 mph, the fan is useless.  There is enough ram air flowing through the radiator to keep the coolant from getting too hot.  The shroud helps direct the air so that the fan is more efficient.  I've always looked at the flow, through the filler neck, to reassure me that there's good circulation.  I just recently read of a way to check the thermostat while it's still in the vehicle.  Use a thermometer (I'm hoping those laser versions will work also) and measure the temp at the top of the coolant level just as the flow stops, i.e. the thermostat is closing.  Clever.

Your issue is under load/ at speed.  To me the pinging noise is a symptom.  I'd hesitate to speculate as it may lead this discussion off into an unrelated rabbit hole.  I think your timing adjustment for testing was a good idea. Have you observed any difference in oil pressure when the noise starts? 

After you shut down, it continues to overheat to 220.  That's concerning.  To me it should be: if no fire, then no heat.  Sitting hot is one thing. Temp climbing is different.  Where are the thermostats coming from that you've experimented with?  Local, brand name, or mail order?

Item 6 above on the 26 April post.  "No sign of the lower hose collapsing."  When it's not hot, can you squeeze it flat like the upper hose (open cap to allow displacement)?  There should be a coiled wire (or similar) inside to prevent this.  I've seen them fall out before.