Technical Rebuilt 324 olds overheating only on highway

Chrysler Corp used a water pump with a slower flow on A/C equipped V8s in the 70s. I suppose the temps got hotter when smog regulations came about. So yes, flow speed is not a myth

 

I thought it was not necessarily the higher flow rate not removing heat but the fact that the water pump cavitation creating turbulence in the coolant that reduced its cooling ability when not running a thermostat.

Now back to my last post a couple topics up. Head gasket?

 

If the air bubble never goes away with that raised funnel, then I would think you do have compression getting in the cooling system. A shop sometimes uses a smog sniffer to detect combustion gasses in the radiator neck

 

Yeah you can get them at the autoparts store- might do that this weekend . The only strange thing is that it only bubbles on high revs. The thing can idle for 10 mins and not a single bubble. Is the radiator the only thing on the suction side. Could it be sucking air from somewhere? I mean heads and block were all machined and gone through and it has never overheated just started running hotter. Just don't want to believe it's a head gasket just yet I guess.

 

Did you use the right head gasket considering that you bored it to the 371 spec? If you pull it apart, I'd look carefully at the bore/gasket area you may have a mismatch of

 

Fan can be an issue at highway speeds also,flex fans flatten out at high speed and block air coming thru the rad, and in some cases also an electric fan can do the same thing.

 

the restricting plate in a flat head is to force the coolant through the back of the block.

 

Ok so forget the overheating/coolant issue for now. There is bubbles in the coolant when revving. None at all at idle Did a leak down test which was kind of pointless because it has not been broken in yet but all cylinders were about the same . Also did a block test(chemical test that detects exhaust gases). It was negative I had absolutely no color change. So... Where are these bubbles coming from.

 

Way out in left field but here is the problem I had on my '57 T-Bird. OK at low speeds but overheated on the freeway. Turned out to be a busted diaphragm in the distributer. The only way I noticed it was that the power was pulsing at about 30 MPH. Replaced the diaphragm and the problem went away.

Charlie Stephens

 

I'd go for the leak down test even if you just gut and old plug and weld a fitting to it to hook a male air hose fitting to to put air pressure to the cylinder. That might at least let you know if you have a

 

Thanks! Please read my last post.

 

If you think she has a small head gasket leak due to bubbles, you might drain it completely, heater and all. flush three times until completely clear and pour in a quart of waterglass and then put a big piece of cardboard over the radiator and then drive it until the temp gauge pegs, but stop driving her before she steams.

Shut her off and then let sit over night and then crank her up, filling the rad. completely full and watch for any small bubbles.

If none appear, drain and flush again until completely clear and the add back the antifreeze mixture you want to run and go.

Been there done this twice fine!!

Waterglass is the "industrial strength" ceramic stop-leak ingredient they sell... Probably buy it at a drug store. I still have a quart in my bedroom closet.

pdq67

 

I have had a bypass hose let too much water flow causing it to over heat, a washer in the hose fixed the heating issue

 

Ok so installed a mechanical guage as well as changing thermostat flushing coolant/bottom hose etc. I think the whole problem was related to voltage. -obviously being higher at highway speeds. Took for a short test run and mechanical guage never got above 180. Original resistor guage still climbing up about 7/8 of the way. Let off accelerator for a bit and factory guage goes down. Mechanical stays steady.

 

If you suspect your lower rad hose is sucking closed at speed put 2 or 3 hose clamps on the outside, they will prevent it collapsing. If this cures the problem you know you need the spring. A quick test that avoids the need to drain the rad and remove the hose.

 

Thanks for posting the answer. After reading all of the posts and guessing along with you it is great to hear the actual result.

 

You might have a simple voltage regulator issue! I would check the voltage while driving on the freeway. The ammeter might show more charge than it should while the battery is charged, but it does not show the actual voltage going to battery.