Breaking in a new refreshed motor with a roller cam on the highway about 2500-3000 RPM for 30 mins and the engine temp gets to 210-220, once I get off the highway and go light to light temp drops to 160-170. Upper rad hose is soft once I stop after light to light, is that normal? Doesn't sound right to me. Would it be the rad cap that I have not changed? Temp outside is about 14 Celsius or 60 Fahrenheit

I lost about 2 inches of coolant from the overflow hose, there was coolant on the underbody of the car from the highway speed. The overflow hose has a metal piece that is pressed into the rad cap area and is lose is that a problem?

1969 L46 with AC no expansion tank, new temp unit in the block with no pipe thread, new 180 high flow thermostat that was tested before install, re-corded the original 3 core rad which takes almost 16 litres of fluid and new water pump. Watching it warm up with an external laser temp tool on the thermostat area which is close to the reading on the temp gage, gage looks close to 180 and the laser shows about 185 and the thermostat opens although the amount of water circulating through the rad wasn't Niagara falls (which might be normal) but I am in the driveway.

City driving everything seems good, only the highway load seems to push the temperature. The previous motor before I wiped the cam didn't have any issues on the highway, nothing on the cooling side has changed other than the thermostat and I changed it because the other one was stuck closed.





Dealing with the rear main seal is hard enough but this too

 

Well a cap is a simple and inexpensive thing to try.
another thought would be ignition timing. Are you running a vacuum advance can? How much timing is it putting in? At what vacuum is all the timing in? Do you know how much vacuum your engine is pulling at idle? Is the vacuum can matched to the level of vacuum the engine has?

 

Starting with the basics of cooling. At highway speeds the engine is laboring more than city driving obviously. More labor = more heat.

Overheating at idle is an Air Circulation issue.
Overheating at speed is a Coolant Circulation issue.

In the first scenario you are putting around at 20, 25, 30, MPH. Not much air is forced through the Rad, but the W.P. is keeping up just fine.
In the second scenario you are getting 60, 70 MPH wind through the Rad but the W.P. can't keep up.

Having said that, why is yours overheating at speed? It's getting plenty of air, but maybe a blockage with the coolant. One thing to check is the Lower Rad Hose.
Its imperative that a metal spring be placed inside to keep the hose from collapsing.

And your temps are not horrible. Just notable.

 

Total timing at 3000rpm is 34 degrees and idle was mid teens but I'll see if its moved off the original setting. I can probably add more timing but I was keeping it a little lower for break in, I am running 94 octane gas. I haven't gotten to the engine vacuum yet but I will dive into that tonight and see.

 

Yes the lower rad hose has a spring in it, it was a new hose and I haven't put many miles on it. Your right temp is not horrible but it's seems unusual for it to rise on the highway to 210'ish and cool down in the city to 170'ish, I would expect it to be a little tighter range. Temp kept slowly rising on the highway and it would have gone higher if I kept going. Rad cap was warm but it wasn't hot after a 45 min drive, not sure if that is a blockage or not enough pressure in the cooling system? When the cam was replaced the shop ran hot water through the engine to clear out some sludge that was in the thermostat area of the intake, maybe that are some chunks stuck somewhere but I'd think city driving would also cause the temp to rise.

I'll put a new rad cap on for $8 then I can make an assumption for now that it's not the issue. I'll check the timing and vacuum then burp it and go from there.

 

Mine is the same way: 175* city & 205* highway. But mine is turning four grand with 4:11s in the rear.

One thing you could try. Red Line Water Wetter. Small plastic bottle, Advance auto, $12. Its a silicone coating that assures the coolant picks up heat off of cast iron.
Its not snake oil. It really works. Results will vary but it dropped my temps about 15*

 

My cooling system is really hard to burp. I have to turn on the heater to get all the air out of the system as I add coolant mixture.

 

If you don't have the foam strips in, on the radiator and radiator support, a C3 can run hot on the highway. Also do you have the chin spoiler? That helps a lot.

 

I'll look into that after exhausting the current list of checks

My blower fan isn't working and I have the AC vacuum shutoff value in the supply line to the heater core that I am not sure if its open or closed (assuming open). Getting the heating system going is on the list, not sure if that impacts cooling flow unless there's air in there
Yes all new foam strips so I should be getting good air flow into the rad, I don't have the strip that goes on top of the rad support between that and the hood on yet...yes on the list. I do have the chin spoiler but I haven't put it on yet...its on the list

Deep down I wonder if its a head gasket

 

"Deep down I wonder if its a head gasket "

Have you re-torqued the head bolts yet?

 

Then I'd give in to my inner thoughts and dreams and get off course then who knows what the orange thing would turn into... . I always think the worst because that's how things usually go for me...the rebuilt original motor was out because the flat tappet cam according to the engine builder "never seen that before" and then motor was out again because the rear main seal was a diarrhea seal plus the tranny joined the fun...so third time I'm guessing is what?

So no haven't re-torqued head bolts yet. Trying to confirm timing tonight but the tape I had on the harmonic balancer didn't stick so I'll go get a good timing light tomorrow that doesn't need the timing tape for advanced timing setup.

Did get the new rad cap today but the AC Delco place gave me a 13psi cap when it should be a 15psi cap...so another parts run.



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Update:

• Replaced the rad cap yesterday, had to go with a 16psi cap because all the local auto parts vendors only sell 13psi rad caps (15psi is the original with the brass rad). I did run the car for 5 mins after while I was checking idle timing, after sitting for an hour I took the rad cap off an there was some pressure released...haven't heard that this year
• Reset all the timing today
  • Set it at 36* at 2800rpm with not springs in the distributor and no vacuum
  • After it was 6* at 800rpm with springs no vacuum advance
  • Checked again with springs at 2800rpm and it was only 22*
  • So went to the local performance store and got a spring set
  • Put the lightest springs in and it was 36* at 3000rpm and idle was 12* at 800rpm...so timing good for now?
• Vacuum advance
  • I have a MS 360 12 vacuum advance thing in the distributor (I believe it is the original distributor)
  • Vacuum is hooked to the front of the card so not manifold
  • I tested the distributor vac advance and it holds vacuum
  • 1300rpm the vac line from the carb has 7 on the gage
  • 1500rmp its 11
  • 2200rmp its 18
  • There is no vac at idle not sure if that is a problem, do I need to go with manifold vac?
  • I am not sure what the distributor vac advance I have will produce but I saw one reference being 14-16 crankshaft degrees...so that would give me 50-52 all in?

Took it for a 45min test drive, did some city and a bit of highway, temp gage never went above the 160* mark. When I got home and to my surprise the top rad hose had pressure Checked the temp with the laser and it was 200'ish at the thermostat housing area so the car temp gage is off...read an article about adding a resistor to the line because the temp sensor in the block is new. Car ran ok, has power but doesn't scream but it is not a race car like some of my previous adventures. Next step is the carb.

Never burped the system, I did buy a no spill rad funnel kit but that might not work with my car because I don't have an expansion tank. I have to fill my rad about 2" below the top of the rad cap and the no spill thing will fill it to the top...I think

So I am feeling better and will take it for a longer run on Sunday and see, gonna rain a bit tomorrow and there's a lot of house stuff to do. Thanks for the support!

 

Bring a gallon of water or a gallon of pre-mixed coolant with you at all times in case a coolant leak occurs.

 

Does the lower radiator hose have an anti-collapse spring inside of it...or is it a corrugated hose that will not collapse? If not, at speed the suction of the water pump will collapse the lower radiator hose and keep the pump from supplying adequate coolant to the engine. Especially if you installed a hi-flow water pump on that new rebuild....

 

I think the radiator cap is going to solve your problem, losing coolant through the overflow hose at 210-220 degrees just doesn't happen. Water boiling point is 212F, at 15 psi (radiator cap) that boiling point is increased to 249.8F. A 50/50 mix of water and antifreeze will add 11F buffer to those number so in reality the car pukes out the overflow when the water temp is 260F or higher. A defective/worn radiator cap that will not allow the cooling system to operate at 15 psi will allow coolant to exit the radiator via the overflow hose, in your case that is happening between 212F and 220F.

 

Sounds like you have the cooling end sorted, but to keep your car running as smooth and cool as possible, especially at idle, you want your vacuum advance hooked up to manifold vacuum, not ported carb vacuum.

 

Yes the lower hose has the anti-collapse spring in it and yes I have a high flow pump and thermostat

Good to know! Yes I think it was the rad cap

I'll switch it to manifold later today