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Discussion Starter #1
Maybe someone can figure this one out . My temperature gauge will slowly rise from 0 to 230 , then drop quickly to 175, it will then fluctuate between 175 and 190. I have replaced the thermostat with a 180 degree one with two 3/16 holes drilled in the flange to get rid of the air, have changed the temperature sending unit , still having this problem. :confused: Joe
 

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Doc here,

You probably still have air trapped in the system..read this quote from another post..

docvette said:
re: Cooling system problem or not?

--------------------------------------------------------------------------------

Doc here,

If you have rapid excursions of temp readings on your gauge, The prime suspect is Trapped air in the Cooling system.

To Burp the system, The best way is, place the front of the car on a slight incline, Fill the system AND The recovery tank.

Get a lower pressure than normal Radiator Cap, Install that, Start and warm the car..Monitor the Gauge, Do Not let it Overheat!!

Once warm, stand back a bit, and watch and listen as the system clears it self...It will expel coolant into the recovery tank, and draw back pure coolant replacing the airspace..

It looks terrible and sounds really bad while your doing it, but it is the best way to clear the air. Run until it no longer expels air..and DO Not let the recovery tank run dry.

When your satisfied, Shut the engine off, let it cool, and replace with the proper cap, lower the front and test drive it.

Air can become trapped in a water pump, and reduce or even stop cooling, Also, A Temp sender can not read air..Hence as water Flows past it the bubble moves a bit, as it settles back the bubble goes back surrounding the sender..High..Low.

Try that and let us know the result.

Doc
__________________

Doc :pimp:
 

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I agree with the air thing... but also use a multimeter to test continuity between the sender body and the manifold or other ground source. Mine didn't get a good ground and it would not give accurate readings since the resistance between the body and the manifold artificially changed the gauge. And yes, it does fluctuate. Just adding pressure from your meter's probes will probably cause massive fluctuations.
 

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Discussion Starter #4
I don't believe there is air in the system. 1. I have drilled holes in the thermostat
to bleed air out. 2. This has been happening for over two months. 3. I left the radiator cap off to help let air out and have installed a overflow tank. I am just getting fed up with this gauge not working correctly.
 

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It doesn't matter if you've drilled holes in the thermostat. The coolant system is closed. Its like the air in the top of a water balloon. You can't get it out without opening the balloon.

The thermostat never "seals" anyway, so drilling the stat won't help air get out.

You'd be surprised at how much air can be in a system. I've been running mine for three months since the new radiator and there is still a pocket of air in the upper rad hose.
 

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Doc here ,

Curtis is 100 percent correct..

No matter how many holes you drill in the thermostat, It can still trap air..

just leaving the cap open for months at a time won't do it either..The air is going to settle in the highest cavity it is going to find in the area , (including the Water pump) and left to it's own devices won't evacuate from the system.

You need a closed system (Recovery Kit ) , lower pressure cap (for ease of blowing the air off) and a circulating engine to evacuate the air properly..other wise it will settle in places that won't allow the bubble to move toward the radiator and overfiller..AND you need a FULL recovery tank so the evacuated air has a draw back of coolant..

If you Still feel it is the sender / Gauge, Get a hotplate, Accurate Lab Thermometer , and a pan of water..

Remove the sender, ADD a bare wire around the Sender body for ground, plug the sender back in, and immerse the sender in the pan of water..

Heat to boiling and compare the readings against the Gauge in the car...watching for "Excursions". If good, cool it off, to around operating temp and maintain the heat and sustain it,(as close as possible) Watch your gauge and see if it "jumps around" If not, shake the harness while someone watches..If it won't move, You have the only possible other suspect..Trapped Air.

Doc :pimp:
 

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try replacing your thermostat with a High Flow model from MR gasket or Mildon. If you are running a high flow water pump the extra presure the pump creates can actually hold the thermostat closed. I had a similar issue with a stock tstat with holes in it. I replaced it with the Mildon model and have had no issues.
 

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johnsongrass1 said:
If all else fails, pick up your car and shake it.

Doc here, :pimp:

" open can away from your face, Can cause serious Eye injury.." :D

From the side of a soda can, safety Warning.. :rolleyes:

Doc :pimp:
 

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Discussion Starter #10
I'm going to try Doc's post , raise the front of the car , fill the recovery tank and let the car run. Most likely won't get to it until the weekend will post the result. Joe
 
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