cooling issue,i can't figure out

I have a sbc with 11 thousand miles on it,when I took it out for the first spring ride I noticed it wen't up to 220-230 then back down to 185,this motor never went over 200-205 sitting in traffic,so I figure i'd change the thermostat and put in another new 180 which it had,fired it up same thing,put a new 195 electric fan sender,still the same.wierd it never did this before with 11 thousand miles.what do ya think guys,thanks

 

Does the fan come on at 195 ? Where's the temp. Sender located? Do you have one of the laser lite temp. checkers? They are cheap now.

 

If you have ac make sure nothing's built a nest between the condenser and rad.

 

if its goin up then back down gotta be thermostat or fan thermostat switch i,d bypass fan switch to see if thats the problem

 

the fan comes on at 195,and the sender is in the front driver side head,i also lifted the front of the car and tried to burp the air out,it never got warm before

 

oh yeah,this will only happen once after I start the car and will be fine until I shut it off and it cools down for a long time and I restart it again

 

The temp swing happens while driving..........or while sitting in traffic?

Regardless, it could be a bad ground.

 

Or has possibly crawled up the exhaust and partially restricted it with a nest. Throw a vacuum gauge on it.

Bob

 

Hows the coolant look? older coolant looses its ability to carry heat away as well.

 

doesn't matter if driving or sitting still,i will start the car go for a ride temp will come up to 220 and then go back to 180-185 and stay below 200 until I shut it off and the next day it does it again,i've never seen this happen in my life

 

new thermostat,new sender new anti-freeze,gauge is good because it works fine for over an hour of straight driving

 

Try drilling a 1/8 th hole in thermostat - if that helps I would think air is building up in engine. Then it would be time to look at head gaskets . Just a thought.

 

I have had several brand new thermostats fail right out of the box - four in a row once. Always test them in a pan of boiling water - just because they're new doesn't mean they're good. As Okatoma cruiser says, drill a 1/8" relief hole in the thermostat. I have a car where the temperature gauge works fine as long as I have the A/C on but the moment I turn it off the indicated temperature climbs to 250-260˚F. Replaced the sender with a known good one from another vehicle - no change. Temp gauge will have to go back to manufacturer for repair. Check your hoses to see if there are any cool spots (air pockets) and drain the system and refill with new coolant.

Get a cheapie non contact laser thermometer, get the car up to the high reading then pull over, point the temperature gun at the radiator - top, bottom and sides and do a spot check on the radiator temperature so you know for sure....

 

Do a couple tests the next time you start it. Let it idle with the radiator cap off and watch the gauge. WHen it gets to 180 you should see flow in the radiator. If not, then wait to see what temp flow begins, and that's when the stat is opening. If it's after 180, then the new stat is bad.
Also watch to see what temp the fan finally switches on. If it's higher than the setpoint, the switch needs to be replaced, or adjusted lower.

 

I know the 1/8 hole trick and thermostats can be bad out of the box but why would they only not open the first time and then be fine,two of them doing the same thing is,what are the chances,i have checked the hoses, every thing that may be the cause,that I know of

 

As I said, I had four in a row fail right out of the box - yep what are the chances? But they did. Do the temp gun thing so you know what is happening or buy a Thermocap - not pretty and a bit streetroddy but it will tell you where the coolant temperature really is....

 

Drill the hole. When you first cold start the engine and is comes up to temp, the core of the engine gets hot faster then the water around the stat bulb. When the stat finally sees water hot enough to open it the core water can be quite a bit hotter. Once the stat opens that core water flows past the temp gauge sender and you see a rapid spike on the gauge then it stabilizes. The hole or a bypass hose will allow water to circulate by the stat from the core of the engine. That let's the stat see the hot water sooner and open earlier.

 

Make sure the lower (return) radiator hose still has a good spring in it and isn't collapsing.

 

Do you have a mechanical gauge or electric? When I ran a mechanical gauge, it seem to take a long time to read and when it did, it jumped to 230, then came down. I switched to an electric gauge and it work right away.

 

I think AG F/C nailed it. If the sender is mounted in the intake manifold (as many are), the gauge will see the same water temp as the thermostat. With the sender in the head as yours is, the gauge is seeing water right off the exhaust ports, probably the hottest point in the engine at any given time. The thermostat will take a little longer to open, as it is getting water from ALL points in the engine.

My advice... If it only does it once as the engine warms, and it's not kicking water out when it happens, don't worry about it.

 

the thermostat already has a hole that came with it,it has a little piece of brass that floats inside the hole to let air pass by,i will drill another hole if I cant find the issue,just seems strange it didn't do it before.ag f/c has the right idea of core getting hotter faster but the bulb in the thermostat sits in the water below the manifold so the water temp is always the same around that bulb

 

it doesn't puke it just gets hotter than it ever did,and that bothers me.thanks guys,i will find out why and let you all know.thank for the input

 

I have been trying to find a spring for my radiator hose and it is impossible! Anyone have a solution?

 

Use a metal tube and short connector hoses. That's the safest way to go in any case.

 

And once you get the engine up to temp, the stat is swing hot water already so it responds quickly the the spike won't occur. The little rattle deal is shut off by the water pump pressure and won't let water by. One 3/16 hole should do it. Might warm up more slowly but you won't see a spike.

 

Thats what I do with all my cars.

 

ag f/c i'll drill the hole,i've tried every thing else.thanks

 

Tanks!

 

You didn't mention if you had your heater bypass hose on the water pump hooked up. I had the same issue and determined the cause to be as AG f/c mentioned. My heater bypass on the water pump was plugged as I was told it would be okay that way. My thermostat was drilled but may not have been enough. I actually had (3) 1/16" holes in it but was not enough. To solve the problem I looped my heater bypass from the water pump back into the intake manifold so the pump would circulate water in the block/head until temp warmed up enough to open t-stat. . . . Problem solved, no more temp spikes!
Attached are a couple pics of before and after of what I mean.

 

ag f/c I did drill a 5/16 hole and problem solved thanks