Does Anyone Run Lower Radiator cap Pressure ?

[Jetronic]

cavitation kills pump impellers, which is quicker to occur at lower pressures. when cavitating, flow isn't going to be as goodas it could be aswell, leading to overheating of engine parts and boiling of the fluid beyond nucleate.

My car comes with a 1.4 ATM cap, so that's 20 psi. I'll leave it as is... but on another car with 20 psi cap I also ran with the cap loose when the radiator was leaking, without issues. I never did use all of the potential of the engine though.

 

[HerrStig]

Originally Posted By: Lubener
Those rebuilders do not have much confidence in their work if they believe six pounds less pressure will have an effect on an engine. It simply raises the boiling point of the coolant, no more no less.
MORE pressure raises the boiling point.

 

[philipp10]

another "if I can do it different than the original engineers intent" posts. Why would you want to? Some of the stuff on this site gets to be just silly.

 

[Vikas]

what causes the pressure to build up in the cooling system? Is it just because it is closed system and being heated causes the pressure to build up? Water pump has fins, so it is not positive displacement pump, thus by itself, it can not build excess pressure.

isn't the pressure stamped on the radiator cap is the "limit" pressure and NOT the "running" pressure? At normal operating temperature of the engine, one should not have the radiator cap opening up!

 

[TFB1]

Originally Posted By: Vikas
what causes the pressure to build up in the cooling system? Is it just because it is closed system and being heated causes the pressure to build up? Water pump has fins, so it is not positive displacement pump, thus by itself, it can not build excess pressure.

isn't the pressure stamped on the radiator cap is the "limit" pressure and NOT the "running" pressure? At normal operating temperature of the engine, one should not have the radiator cap opening up!

Ever hear about water expanding as it heats??? No doubt the ethylene glycol in anti freeze has a even greater expansion rate...

Originally Posted By: Jetronic
cavitation kills pump impellers, which is quicker to occur at lower pressures.


[censored], I bought my first car in 1966 and EVERY pump that's failed in those almost 49 years was due to seal leakage(yes I've replaced every one), the impellers were fine....

 

[Jetronic]

Originally Posted By: TFB1


Originally Posted By: Jetronic
cavitation kills pump impellers, which is quicker to occur at lower pressures.


[censored], I bought my first car in 1966 and EVERY pump that's failed in those almost 49 years was due to seal leakage(yes I've replaced every one), the impellers were fine....


I've seen other failures than just leaking. Impellers are a huge concern, though cavitation shouldn't be a problem in practice. But I wouldn't run without pressure in the system if there's any chance of going over 200°F.

 

[Lubener]

cavitation kills pump impellers

I don't buy that. I have an old Ford tractor which has an unpressurized cooling system, That water pump lasted over 50 years before it started leaking. The seals went bad not the impeller.

 

[TFB1]

There was pump impeller issues on some mid/late '90s Fords, problem was cheap impeller combined with lack of cooling system maintenance, not lack of pressure...

 

[mlatour]

I ran both my 1976 K5 Blazer 5.7l
and 2004 Ram 1500 4.7l
with 7 psi caps for 11 years each,
never a problem.

Yes it 'might' have lowered the boiling point,
(never a problem even off-roading with the K5)
but I figured less pressure was overall easier on the hoses/radiators.

If a 7psi cap was available for my new F150 3.7l
I'd probably run it on that too as well.

 

[eljefino]

Originally Posted By: Vikas


isn't the pressure stamped on the radiator cap is the "limit" pressure and NOT the "running" pressure? At normal operating temperature of the engine, one should not have the radiator cap opening up!


Sure, why not? It burps air, coolant, or water vapor down a hose where it hopefully hits an overflow bottle, condenses, and sticks around to get slurped back in when things cool down. If it's on a surge tank (or pre 70s car without overflow system) it holds down a layer of air that holds down the coolant from possibly flash-boiling.

 

[another Todd]

I do use lower pressure caps and have for 25 or 30 years. Back then they were easy to find, today they are a little more difficult to find a lower pressure cap due to the many different styles of caps. I usually try to drop the PSI by 3-4. I have never had any issues with the lower PSI, and my cooling system parts seem to last forever.

BTW, I also use Barr's stop leak in everything I own as a preventative measure, and again, never a problem.

 

[TFB1]

Seems to me this thread is busting a lot of myth and misinformation...

 

[The_Eric]

Originally Posted By: TFB1
Seems to me this thread is busting a lot of myth and misinformation...



Not really. Someone writing in and saying my half a century old tractor, or my truck or whatever all work fine with less or no pressure in the cooling system is not proof of anything. Anecdotal at best.


Cavitation and flash boiling/local hot spots are real and do happen. I pulled a 351 Cleveland apart once that all kinds of pock markings in the backing plate of the water pump. I've seen impellers eaten to near nothing. Plenty of diesel owners will tell you about cavitation too.


Read the engineering data on it- if you'll believe it. Do you REALLY think that the manufacturers would increase the chances for cooling system leaking and causing warranty returns if there were no other benefits to it?

 

[crazyoildude]

you have to hear some of the things some of these engine shops do I know one shop that until a few year ago only used 10w30 in everything and before that about 20-25 years ago used strait 30 in most engines they built. We check the caps and if they need replacing we replace them that goes for the radiator also of course that is at an extra parts charge.

 

[yeti]

Originally Posted By: The_Eric
Originally Posted By: TFB1
Seems to me this thread is busting a lot of myth and misinformation...



Not really. Someone writing in and saying my half a century old tractor, or my truck or whatever all work fine with less or no pressure in the cooling system is not proof of anything. Anecdotal at best.


Cavitation and flash boiling/local hot spots are real and do happen. I pulled a 351 Cleveland apart once that all kinds of pock markings in the backing plate of the water pump. I've seen impellers eaten to near nothing. Plenty of diesel owners will tell you about cavitation too.


Read the engineering data on it- if you'll believe it. Do you REALLY think that the manufacturers would increase the chances for cooling system leaking and causing warranty returns if there were no other benefits to it?


I know of 2 mechanics that routinely change out 16lb. caps in their customers' vehicles to 7lb., as well as their own vehicles. they've been doing it for years, without issue. logic being that it's easier on rad,and heater cores.
obviously, there are 2 different sides in this thread.

you know about which you speak, per your posts, re:vehicle maintenance.
a 7 or 13 lb. cap will lower boiling boiling temps., but not to the point where it should be an issue.as well, cavitation is a possibility.
in your opinion, are there any other possible issues that could cause problems ?

 

[another Todd]

I would imagine water pump cavitation with damage might be a thing at very high RPM and/or with a poorly designed or inferior metal impeller.

 

[JHZR2]

Ive known a few folks who have put evans waterless coolant in their MB diesels, with no pressure, and have been really happy. There is something to be said about less stress on the cooling system in old vehicles.

That said, I run water and the cooling systems are more or less all original in my 34, 33 and 24 year old vehicles which Id drive across country tomorrow...

 

[Kruse]

While I think you could lower the pressure on certain vehicles, I don't think you want to do it to all of them.
While the guy might come across as being brash, take a look at "$5 PART WILL SAVE YOUR POWERSTROKE FROM SELF DESTRUCTION" on youtube. This guy seems to think that the powestroke diesels don't have enough pressure from the factory caps.