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Author Topic: Radiator and engine temp  (Read 1466 times)

Tom Atkinson

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Radiator and engine temp
« on: May 23, 2008, 12:51:33 AM »

This started in the feeling hosed post.  Some felt a new one on this topic would be good.
 
When running the hose from my engine to the rad is easy to squeeze shut.    I'm told it should have some puressure in it.    I think I found the problem and need a new rad cap.
 
However it prompted these question in my mind. 
 
If this is not working right should or will the temp light come on?  
 
I read the tech manual and it appears the temp guage is working correctly. When I go to start the engine the red light pops on for a second then off as the manual says it should, then the green cold light till it heats up.  Hot never comes on.
 
Also if it has no pressure does it mean the system is not circulating and cooling?
 
If its the stat it looks like a pretty simple repair, new gasket and stat.
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Tom Atkinson

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Radiator and engine temp
« Reply #1 on: May 23, 2008, 06:36:15 AM »

I should have included this in the 1st post. 
 
I'm thinking its the cap becasue if I squeeze the hose while the engine if off I can hear air coming out of it.   Is my thinkng correct?
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Steve

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« Reply #2 on: May 23, 2008, 03:41:00 PM »

Yes you are.  Look inside the cap and see if the rubber is still in place or if equiped, the brass sealing ring is in tact.
 
If in doubt, get a new one.  It's a 9 Pound Cap
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Tom Atkinson

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« Reply #3 on: May 24, 2008, 08:05:11 AM »

Yeper the brass is cracked.  
 
When I went to get the new cap everyone told me 13lbs was showing on the parts list.    I could not find a 9 lbs.  Only found a 7 lbs and several in the teens so I left to come here and discuss.  What is the advantage of using the 9lbs cap?  Will it keep me from blowing the radiator or as one place said allow it to run cooler.  If it's cooler how does that work?
 

I figured while we are talking about it I might as well change out the fluid too.  Is it safe to run the engine with the drain plug open and running water from a hose into the top to flush the system out? 
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Bill Mounteer

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« Reply #4 on: May 24, 2008, 10:28:23 AM »

The higher the cap pressure, the hotter the rad can get before the coolant boils, but higher cap pressure will also stress any weak spots in your cooling system and cause leaks. Cap  pressure release point becomes most important after you shut down a hot engine, the coolant will boil inside the engine and if the cap doesn't allow the system to vent you will start popping hoses.

Modern systems allow the rad to vent into the overflow bottle and then suck the coolant back in to the system when a cold engine warms up. Our old technology vents to the road so if the cap release pressure is too low, you quickly end up with low coolant levels and air in the system.

So, when in doubt, buy the cap with the higher rating. Just don't go nuts and get one way to high.

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Steve

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« Reply #5 on: May 24, 2008, 06:33:55 PM »

Then use the 7 Pound
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Bill Mounteer

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Radiator and engine temp
« Reply #6 on: May 24, 2008, 07:05:06 PM »


If you use the 7lb, keep an eye on your coolant level and if you start losing coolant, change to the next higher size.

Keeping your system under pressure increases the temperature at which the coolant starts to actually boil. In an ideal world if you could use a high enough pressure the coolant would never boil and a relief valve wouldn't be required. Unfortunately, in the real world, coolant expands as it gets hotter and you reach a point where some must be bled off otherwise the system would rupture. Modern systems with recovery bottles handle this problem, but ours don't. So we have to juggle with cap release numbers to achieve a balance so that the system doesn't boil during normal operation and doesn't loose too much when the engine eat soaks after heavy use on a hot day.

Cap pressure values recommended are usually based upon elevations close to sea level and need to be increased if you live at higher elevations such as  say Denver as compared to  LA.

Edit:

I looked at the Shop Manual for my car and it calls for a 190 deg thermostat and a 16 lb rad cap.  In the section on testing,  the cap should open between 14 and 17 lbs  and under no circumstances should it allow over 20 lbs of pressure.

BTW, the pressure cap does not affect the engine temperature, so who every told you that a 7 lb cap will make the engine run cooler is full of crap.  The only way to do that is to use a thermostat set for a lower temperature.
 

Fury4402008-05-25 00:17:14
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Dan Cluley

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« Reply #7 on: May 24, 2008, 11:23:05 PM »

After a couple of trips to the radiator shop to get leaks soldered up, I switched from the 13 to the 7 lb cap and it has worked fine for the last few years.
If you don't feel like dumping coolant on the ground, and having to check/replace it, it is pretty easy to add an overflow tank.






 
The existing hose should run from just under the cap, across the top of the radiator and down the side next to the battery.
 
An auto parts store should be able to get you a universal tank (I don't recall if they call it a radiator overflow tank, or a washer solvent tank.  I use the same type for both) 
 
There is room between the grill and the radiator support (kind of in front of the battery) and some existing holes in the radiator support to mount it to.  The existing overflow hose is long enough to run through and hook to the bottom of the new overflow tank.
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Tom Atkinson

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« Reply #8 on: May 25, 2008, 01:51:57 AM »

Thanks.  This is great info.  I see the over flow tube and it never dawned on me to check the fluid every now in then.  Luckly I've never had any problem and now I know to keep an eye on it to avoid one.
 
On my other question is it safe to run the engine with the drain plug open while running water into the rad in an attempt to flush it out?  I'm thinking at this point no since it has to have presure.
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Steve

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« Reply #9 on: May 25, 2008, 05:58:55 AM »

Oh Stop Bill
 
In those days they didn't fill them to the neck like we do today.  7 Pound is what they were packeaged with back then.  Look it up
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Bill Mounteer

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« Reply #10 on: May 25, 2008, 09:45:26 AM »



Quote from: POLARACO
Oh Stop Bill
 

I did and all the manuals I read said the stock cap is 16 lbs and if, when tested, it was out side of a 14 to 17 lbs operating range, then a new cap was required. The Shop Manual also said when pressure testing the system never go beyond 20 lbs so I take that to mean the system is designed to operate at an 80% load point. A 7 lb cap will run the system only at a 35% load but will allow the coolant to boil at much lower temperatures.



The curve above will be less steep for anti-freeze. Adding a pressure cap will shift the boiling point at zero elevation further to the right.  This isn't rocket science, its just the way liquids behave at different pressures and temperatures.

IMO if you can't keep the system from popping leaks unless you go to a 7 lb cap, then the rad must be close to end-of-life and  any trips through high country should be avoided.  When we drive through the mountains from Calgary to Vancouver you wouldn't believe how many boil overs I see on the side of the road.  The reason, clogged cooling systems and defective pressure caps that can't handle the elevation and lowered boiling points.

BTW Steve, I can post a link but for some reason I can't upload a picture. That mean I've been bad?


Fury4402008-05-25 14:48:12
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Steve

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Radiator and engine temp
« Reply #11 on: May 25, 2008, 05:23:34 PM »

No
 
I guess I'll have to drag out the scanner
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Tom Atkinson

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Radiator and engine temp
« Reply #12 on: May 27, 2008, 05:38:23 AM »

OK what did I do wrong?
 
I drained the radiator then ran fresh water through it.  Left the plug open as instructed on the bottle and ran water from a hose through system while the engine was running with the heater on high for about 10 mins.   Shut off the engine and let it drain until no more fluid came out.  I then closed the plug and filled with 1 gallon of anti freeze.  Here's where I'm messed up.  It would not take any more fluid.   I started the engine and ran for about 1 min thinking it needed to draw in the fluid and turned it off.  Opened the cap and it was still full.  So I figured I hadn't run it enough.  I ran it for about 10 mins, let cool and checked again.  Still full?   The hose off the stat is staying hard when it heats up and back to soft when cool too.
 
Chrysler3002008-05-27 10:39:13
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Bill Mounteer

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Radiator and engine temp
« Reply #13 on: May 27, 2008, 09:46:36 AM »

When you ran the engine did the temp gauge get up to normal? I'm wondering if you ran it long enough to get the thermostat to open, if not you probably only flushed the rad and not the engine. I haven't flush a system for awhile but my method was to open the rad drain cock and put the garden hose in the filler at the top and adjust the garden hose to put out water just fast enough to keep the rad full. Then I'd let it sit and idle until the engine reached operating temp and the water coming out of the drain cock ran clean. Finally to drain the engine, I'd pull the thermostat housing and stick the exhaust hose from my shop vac in the hole (fits nice) and blow the water out. After about 15 min of blowing, I'd shut the drain cock and pour antifreeze into the thermostat hole to fill the engine, install a new thermostat and then fill the rad. Start it up and keep adding antifreeze until the rad level stabilizes after the new thermostat has opened. Even after all that, I still usually had some air in the system,  usually in the heater, but a short drive around the block would usually get that to move. For the next few days I'd recheck the coolant leverl and keep it topped up.

Rather a Mickey Mouse solution, but it worked!


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Tom Atkinson

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« Reply #14 on: May 27, 2008, 10:34:28 AM »

Pretty much did what you did 440 but without taking off the stat.  I ran it till I had  clear water coming out.  Must not have been long enough I didn't think to see if the return hose on top was hot.
later I ran it later for about 20 mins to make sure I had the temps up etc.   When I looked in the rad today the fluid was green and clear.  (we need on of them little smile guys scratching his head).
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