ZZ4, added 385 Fast burn Heads (# 010105117 “GASKET-CYL”, 012464298 “HEAD CYL”) and gaskets from SDPC. Edelbrock Performer Air-Gap. Weiand Aluminum Water Pump. Changed 180 Deg. thermostat 3 times, new 3 core radiator, changed water temp gauge. Problem= Water temp gauge goes nuts, sometimes up to 220-230, then back down to 180 no reason or rhyme, opening heater doesn't help but sometimes, sometimes it goes up sometimes down. What Suggestions?

Drill 6 1/8 holes in thermostat.

Electrial or mechanical guage? Where is the sender located? Are you sure all of the air is out of the system? Are you really that sure?

Just a couple of questions. I leaning on either air in the system or the type of guage ans sender you are using and how the sender was installed. Sometimes using a sealant on the sender will give you a false reading....

If your guage is accurate and there are no air pockets in the in the cooling system you have a mechanical problem. When does all this high temps occure? Setting at idle of rolling down the hwy? If it heats at idle look for air flow issues like core blockage, fan mounted backwards or bad clutch or maybe retarded timing.

Off the subject a bit, but I thought I read that your intake isn't designed for use with Fastburn heads. ????

Does it rapidly increase than fall off? Or is it slow?

My grandfather had a problem like that at one time, and it turned out he was given a reverse-flow water pump.

The water pump is a Weiand (WND-8240P) the intake is Edelbrock (EDL75161, for vortec heads). It does at idle and speed. The Fan Clutch is new, I spun the other one off within 10 minutes of getting it back together at around 7,500, no damage except the clutch, I then changed the water pump thinking I had damaged the other one with the wobbling, etc., or so everyone says.
The Mechanical Gauge (autometer) goes in the hole for the sender, drivers side of the thermostat, mounted in a adapter supplied. Another gauge provides the same results.
Next I'm trying the bottom hose, courtesy of CarlC, If this happens at idle, I can't imagine the fan being the problem.
Thanks for the replies, keep them coming and I'll report progress from tonight. I'm changing the bottom hose and spring in it and will report from there.

Thanks for all the continuing help.

How did you fill up the engine with water after replacing these items? I'm with Chicane on the air pocket, seen it TOO many times.

Jody

pull off the thermostat housing and thermostat, and fill it up until it is overflowing out that hole.
put it back together
take the upper heater hose off the firewall and fill that until water comes out the heater core.
hook the hose back up
make sure you have an overflow tank. fill that halfway up
put on the radiator cap (get one with a pressure release lever- I'll get to that in a minute)and start the engine, and idle it until it gets nice and warm.
shut it off
relase the pressure with the lever on the cap until it stops overflowing, and seal it back up. this will purge the air.
let the engine cool for a few hours. this will suck coolant back in as it cools, and you will have no air bubbles left.
if that doesn't work, you got something else wrong.

Now Derrik, you gave him the answer!!!!!! Seriously, when you drain the water from a block with a water pump or radiator/change, you need to remove the thermostat housing and fill the block, then re-install the thermostat and housing and continue to fill the radiator as Derrick stated. If you just try to fill the radiator you'll have a big air bubble at the top of the engine which usually won't even allow the thermostat to open when fired (no fluid). It makes the temp gauge go whacko as well as the water temps in the engine as they're not re-circulating.

Good advice.

Jody

I drilled 6 1/8" holes in the thermostat, now it runs at up to 220 degrees but doesn't go wild like before, but it cannot absolutely be running at 220 degrees, I think, because it'd be pinging, boiling, etc. I have not filled the block THEN put in the thermostat, I'll try that but I'm thinking this is a RPM AIR GAP for VORTEC heads, 385 fast burn, the water passage into the head narrows a lot drivers side of the thermostat and the temp gauge goes right in the middle of that water flow. I used an infra red thermometer on it today and the temps all around are 135 - 145, etc., except the housing the gauge sending unit is in, it was the hottest, about 165 - 175, of everything.

Maybe I need to move the sending unit?

I'll keep the post current.

I like the thermostat installed backwards trick. Some times it's an easy mistake. Kinda made me wonder if it's in backwards since the heat sensitive spring wont get the heat till it's pounded with heat then opens a little too late like you are getting.

Sorry but I didn't have the time to read all the fine responses but I had this same problem when I installed a mechanical sendor in my Performer heads. It turned out that the sensor was physically touching the inside of the head casting. I moved the sensor to the front of the Performer RPM intake and no more erratic temps.

The thermostat is installed with the large round spring low and the domed part topside.

If the sending unit was mounted up front, where and how, was the adapter used?

Get an accurate thermometer (usually a thermometer used for food will work, available at most grocery stores) and uncap the rad. cap and run the engine, letting it warm up completely. Hold the thermometer tip in the water. It should give you an accurate reading, both with the thermostat opened and closed. You should also be able to see if you are getting a good flow of water once the thermostat opens.
It sounds like you may have an inaccurate gauge or air in the system, or maybe both. :cool:

Got it! Had put the high output water pump, wieand, on and hoped it might help with mildly higher temps with new heads. Was at a loss what to do, so changed the water pump (stock chrome from summit, cracked, so I put the original gm one back on) and it works FINE. The high output must have created a vortex of sorts out of the head and between the mechanical pick up and the thermostat. I also found the after-market swivel thermostat housing was not trimmed inside where they welded the hose connection and I trimmed at least 3/8" of material away.
It was, however the water pump that cleared it up. With the 180 degree thermostat in it runs at just about 180 to 185 all the time.

Thanks for all the posts and replies.

On to another problem!

I had a temp gauge reading all over the dial once, but it would read between 150 & 185 with in 30 seconds then back down to 150 and so on........ It happend after I removed the hose from the water pump that went to the intake manifold because my pals were hard timing me for having that hose that they said was doing nothing. All I know is as soon as I removed it my temp gague went crazy.... reinstaled it and no problem! (Edelbrock Air Gap intake, -Vortec Heads)My car does not have a heater, thus the hose.
Just my .02!
Dan.