Technical Temperature gauge jumping up while idling or engine shut off

In my daily driver 64 El Camino I've got a 383 stroker that is very mild ,good radiator ,shroud ,fan etc .I've got a 170 thermostat in it and it rides on the thermostat give or take. sometimes when I come to a stop you can watch the temp gauge and hear a bam! bam !bam !and each time it makes the bam it jumps up 5 to 10 degrees .You can also feel it in the hoses if you put your hand on it while running.once I start driving again it jumps back down and all is good.this only happens when coming to a stop and idling .when I shut the car off completely you can watch the temp gauge jump 40° with the bam noise where it was when I stopped like there's pushing pressure into the cooling system.I just did a head gasket test with the blue dye kit and it turns yellow if you got a blown head gasket but nothing happened with that but it did put some bubbles out which wasn't too bad.I've swapped a couple thermostats and cheched that the flow is good in the radiator I can see with the cap off .any ideas guys?

 

You must be getting air /steam in the cooling system from somewhere. When idling there must not be enough flow to move it so it gets hot and turns to steam which makes the bam noise. Is there any bubbles when you look down into the radiator? You could have a compression leak through a head gasket into a water jacket. Does the radiator ever over flow?

 

Yes I can see a couple bubbles here and there but not much. The radiator does not ever overflow. it all stays inside the cooling system even when it's hot. I run a 13-pound cap. My temp gauge is a auto gauge mechanical one and the sender is in the front of the intake bybthe t statstat so you all know. Compression leaking into the cooling system sounds very probable

 

The air flow through the radiator works on the principle of air moving from high pressure to low pressure. The fan is basically a bandaid for when the vehicle isn't moving and the pressures are static. Enclosed engine compartments are ideal for creating a low-pressure zone and so open compartments may have a potential for issues (obviously, not always). Where is the temp sensor located in your setup? It sounds like you may have pockets of hotter fluid suddenly releasing across the sensor. If perhaps the pick up is located in the radiator, you may have higher temp in the block. Why, I can't say but maybe one of us could spot something if you provide some photos.

Edit: I see you answered a question or two while I was composing my reply. I think you're definitely getting some kind of stratification of the temps, which is apparent on your gauge. The most common reason and easiest to fix is low coolant and/or the system isn't pressurized. Do you have a fluid recovery tank?

 

As far as the temp increasing after the engine is shut off, I think that's normal. The components of the engine are actually higher temp than your 170-ish operating water temp. When the engine is shut off, the coolant temp continues to rise as it absorbs more of the heat from the block, heads, etc.

Lynn

 

The sender is in the intake by the thermostat.it's been happening on and off for about six months but in the last couple months it's almost all the time.

 

I understand that the engine temp will rise when it's shut off but not by 40 degrees in 5 seconds. I've got about five cars here at my shop and none of them raise more than 10 degrees after their shut off. 1 Flathead , a 302 Ford,383 race motor,305 sbc and a stock 327

 

Don`t know if this is a valid answer,but a little trick that I learned many years ago,was to have the front of the vehicle sort of nose high when you fill the cooling system to let any air present to escape.
Having the engine running helps also.
Good luck.Have fun.Be safe.
Leo

 

The bubbles do sound like a compression leak, but I would think that eventually if that was so, the radiator cap would blow to release the built up pressure. Since that is not happening you could have some hot spots in the engine that with the low coolant flow at idle turns the coolant to steam, and that is the bang you here. As the steam goes past the temp sensor the gauge goes up then back down as liquid coolant covers it again. The hard part is finding the hot spots and fixing it. Also do you have a 1/8" hole drilled in the thermostat? That may help.

 

Years ago my 66 El Camino did the same thing with the gauge, It's sender was also in the manifold next the thermostat housing. it would jump up and down wildly in traffic and when stopped it would go up like 40 to 50 degrees. My dad told me to put the sender in the cylinder head and see if it changed. Dam if it stayed steady all the time then and never jumped up and down. My only guess is that there was a more consistent water flow over the sender at the head location rather than right nest to the thermostat that opens and closes the water flow.

That being said, I never had the bang sound you are hearing, but the gauge changed how it acted after I put in the drivers side head between the exhaust ports.

 

I believe it is air pocket is there a 1/8 hole in the t stant?

 

Rotted out lower hose spring? If yes = cavitation.

 

Lower hose good not collapsing and there is 1/8 inch hole in the thermostat

 

Hold a rag in front of the rad and see if the fan is blowing or sucking,does it have a reverse rotation water pump.

 

The fan and water pump are definitely turning the correct way

 

How do you know? Chev has both available. Give us some info,has this been happening since the 383 build.

 

Pulley and belt indicate truck motor in picture

 

No this thing's been fine for a couple years. The actual water pump is a flowkooler pump that I put on about a year-and-a-half ago because the regular ones started weeping out of the hole. It's definitely moving the correct way

 

And the fan is pulling air through the radiator correctly

 

The water pump pulley is one I got off of a truck in the junkyard so that late model truck might have had a reverse rotation pump

 

What did you do just before you started to have this problem, or was it always there?

 

reverse rotation WP looks and bolts up the same fan also.

 

Serpentine belt would be rev .These picture look like a truck,are they the 1964 elky

 

How does it run?

 

Yes I know about the reverse rotation water pump .trust me it is the correct one.Bjr the problem was intermittent for a while and nothing was done before that time oror the time to make it happen it just started happening just about every time I come to a stop or turn the car off now days in the last couple months

 

In the pictures you can clearly see v belts. yes this is my 64 Chevrolet El Camino I drive everyday. it runs great everything is good

 

I see the v belts,I meant the truck you took it off of. You have tried a new t stant?

 

If you see the v belt pulley than that truck I took it off I've had v belts also. I did not take the water pump off the truck. And here's a picture of the elky. cast an eye if you dare....

 

About the thermostats when it started happening I had a high-flow 160-degree thermostat and I noticed one day that it was stuck open because the temp never got up at all so I changed it to a stock style 160 thermostat with the 1/8 inch hole drilled in it.now I have a stock style 170 degree thermostat with the eighth inch hole in it.Thanks for listening and all the help guys it's appreciated

 

Do you have the old t stant?Remove the existing one on put it in water with a temp gauge see if it opens all the way