Radiator problem, temp gauge, leaking blah blah blah

effienut2 · Post by **effienut2** » November 8, 2009, 12:08 am

I just got my '66 back on the road. Had it repainted, new interior, really freshened up. But The temp gauge was only reading 140. I had good heat, coolant seemed to flow well. I changed the thermostat and the same thing happened. Then coolant started to leak out of the radiator cap. So I changed caps and the same thing happened. I put on another temp gauge and nothing happened. I had a small amount of coolant comeout of the overflow tank but the leak came out from under the cap.

The truck was out of commission for about a year but there were absolutely no problems with leaks or temp gauge readings. I put a laser temp gun on the thermostat housing and it read about 190. I don't think I'm overheating but I am at a loss as to what could be causing these problems.

Coincidentally the temp gage reading in my other slick reads about 140 as well but no leaks and plenty of heat with no overheating. I checked for air bubbles but that didn't appear to be a problem in either truck.

So, I am at a loss as to what else to do. Any suggestions here would be helpful and much appreciated.

effienut2 · Post by **effienut2** » November 8, 2009, 12:20 am

The problem truck has a 460 with a 3 core radiator and the other one has a 429 with a 3 core rad. Again. never had a problem with either truck until recently.

Alan Mclennan · Post by **Alan Mclennan** » November 8, 2009, 1:33 am

Have you back flushed the radiator?

Fordman · Post by **Fordman** » November 8, 2009, 3:34 am

surely it had antifreeze in it while it sat. a good flush of the system may help it. i dotn know. if your antifreeze was weak or over diluted with water and the system corroded up while it sat or what.

Brian Taylor · Post by **Brian Taylor** » November 8, 2009, 9:34 am

Be sure you have the right pressure rad cap also.

effienut2 · Post by **effienut2** » November 9, 2009, 5:37 pm

I bought a new radiator cap, will try it out later today. I also will check out the sending unit. If all this fails I'll backflush the whole system and start over. I installed a 16 psi cap.

Thanks for the replies.

jwh f-100 · Post by **jwh f-100** » November 9, 2009, 5:46 pm

How far are you filling your radiator??? I could be wrong but I you fill any of these old radiators all the way to the brim they will push out some coolant..

ICEMAN6166 · Post by **ICEMAN6166** » November 9, 2009, 7:29 pm

jwh f-100 wrote:How far are you filling your radiator??? I could be wrong but I you fill any of these old radiators all the way to the brim they will push out some coolant..

as long as it is above the tubes its ok.
if i fill mine to the cap i will lose some.

effienut2 · Post by **effienut2** » November 12, 2009, 10:39 pm

Well, I put the new cap in place and removed some of the coolant as one member suggested. It works! I do believe that I had too much coolant in there. But the gauge still only reads 140 degrees. I know the engine is running 190 using a laser temp gun.

Is it possible that the sending unit could be the culprit?

ICEMAN6166 · Post by **ICEMAN6166** » November 12, 2009, 11:50 pm

i would replace the sending unit if it does not read correctly.

BarnieTrk · Post by **BarnieTrk** » November 13, 2009, 8:22 am

effienut2 wrote:Well, I put the new cap in place and removed some of the coolant as one member suggested. It works! I do believe that I had too much coolant in there. But the gauge still only reads 140 degrees. I know the engine is running 190 using a laser temp gun.

Is it possible that the sending unit could be the culprit?

Yes.

Not too long ago, I did some work on a friends Wrangler. In the process, I of re-connecting the wiring harness to all the sensors/sending units, I determined that the coolant temp sending unit was corroded badly. Although it had worked fine previous to the engine work, I decided to replace it as it. The new unit read 25*F warmer than the previous unit.

I double-checked the part number and it was the correct replacement part. Just as you did, I used an infrared thermometer ( http://www.instrumart.com/Product.aspx?ProductID=143 ) to check the temp near the sending unit. Sure enough, the gun indicated the temp was 25*F lower than what the gage was indicating. I decided just to leave it. With its over-sized tires, the speedometer reads a little off too, no biggie there either.

BarnieTrk

BarnieTrk · Post by **BarnieTrk** » November 13, 2009, 8:27 am

ICEMAN6166 wrote:i would replace the sending unit if it does not read correctly.

Around here, the friendly neighborhood auto parts stores (FNAPS) won't accept a returned electrical sending unit if it has been installed.
In which case, you won't get any $$ back if you want to return it - you're SOL; Simply Out of Luck!

BarnieTrk

effienut2 · Post by **effienut2** » November 13, 2009, 10:05 pm

The sending unit that's in the truck now has been there for 10 years or so. Then the truck sat for a year or so. I happen to have an extra sending unit so I'll put that one in and hope it works.

BarnieTrk · Post by **BarnieTrk** » November 14, 2009, 8:46 am

Effienut2,
If you're going to pull out the 10yr old sending unit and replace it with a different used one, I'd carefully use a brass wire brush on the threads and bottom to remove any corrosion & oxidation in an effort to clean it up. Most of those senders operate on electrical resistance, so I'd think any scale buildup might adversely effect their performance.
Secondly, I wouldn't use teflon tape on the threads. Use a pipe joint compound or high temp RTV silicone sealant. I seem to recall someone saying

that using teflon tape on the sealing threads on these type of sending units may effect their ability to ground properly and hence indicate a false reading.
Good Luck and keep us posted on your progress!

BarnieTrk