Eagle_Adam Posted February 1, 2012 Report Share Posted February 1, 2012 I just recently got my 74 620 back on the road and a front end collision!!! :cool: New problem is my temp gauge wont read "properly" - L18 stock pistons/stock cam/no head work and a basic empi down draft copy of a weber 32/36. The motor ran before all this work and the temp gauge would go to half way up no prob. I got it warmed up for the first time and took it for a drive, everything is peachy except the breaks and this temp sending issue. So i replaced the temp sender and the thermostat thinking that would do the trick but no luck. I want to head up to the mountain this weekend but I'm not going to risk it if my truck is not up to par. Ideas on what to check next??? Quote Link to comment
Lee R Posted February 1, 2012 Report Share Posted February 1, 2012 I just recently got my 74 620 back on the road and a front end collision!!! :cool: New problem is my temp gauge wont read "properly" - L18 stock pistons/stock cam/no head work and a basic empi down draft copy of a weber 32/36. The motor ran before all this work and the temp gauge would go to half way up no prob. I got it warmed up for the first time and took it for a drive, everything is peachy except the breaks and this temp sending issue. So i replaced the temp sender and the thermostat thinking that would do the trick but no luck. I want to head up to the mountain this weekend but I'm not going to risk it if my truck is not up to par. Ideas on what to check next??? What is "properly"? Too hot, too cold.....erratic, bouncing, or just not reading? I had the same problem recently. Quote Link to comment
Eagle_Adam Posted February 1, 2012 Author Report Share Posted February 1, 2012 ya i guess that would be critical info :rolleyes: - this morning i drove her to work and she never got much above the second line on the cold side - 15 mile drive Quote Link to comment
Lee R Posted February 1, 2012 Report Share Posted February 1, 2012 Since you changed out the T stat and sender, check the wiring. Use a thermal gun on the T stat housing as well just to get a temp reading. Disconnect the wire off the temp sender and gauge and do an ohms check on the wire between the sender and the gauge or put a temporary wire between the sender and the gauge and see what the reading is afterwards. Quote Link to comment
DanielC Posted February 1, 2012 Report Share Posted February 1, 2012 This information is for a 521, but there is a reasonable chance it is similar to your truck. If you remove the wire from the temp sender, and ground it, the temp gauge should read full hot. Disconnecting it and leaving it not connected should make the gauge go full cold. Putting a 40 ohm resistor should make the gauge read "normal" operating temp. Quote Link to comment
ggzilla Posted February 1, 2012 Report Share Posted February 1, 2012 Sounds like a faulty thermostat, but since it happened with the old one and the new one it seems unlikely. For a 620, buy a 116-ohm resistor at Radio Shack or other electronics store and use that to test for 1/2 reading on the gauge. The 40-ohm will work too but would read toward the H side of normal. It's a mystery. Quote Link to comment
Eagle_Adam Posted February 1, 2012 Author Report Share Posted February 1, 2012 i will check all of the above once i get a chance to, thanx for the input. My initial thought was a faulty sender but 2 in a row from 2 different parts stores seems unlikely Quote Link to comment
Eagle_Adam Posted February 3, 2012 Author Report Share Posted February 3, 2012 Use a thermal gun on the T stat housing as well just to get a temp reading. did this and the block reads 145 and the thermostat housing reads 135 :blink: If you remove the wire from the temp sender, and ground it, the temp gauge should read full hot. Disconnecting it and leaving it not connected should make the gauge go full cold. Putting a 40 ohm resistor should make the gauge read "normal" operating temp. Did all of the above and got the described results It's a mystery. still is to me - i was doing some reading and i think im going to put some cardboard in fornt of the rad and see if that helps. I cant be driving my truck if the damned thermostat wont even open :angry: Quote Link to comment
ggzilla Posted February 3, 2012 Report Share Posted February 3, 2012 block reads 145 and the thermostat housing reads 135 Well it is not warming up to normal. You want at least 170 for proper fuel economy and less engine wear. This also shows that your send and temp gauge are not the problem. The problem is it really is not warming up! Is your thermostat installed facing the correct way (spring towards engine side)? Quote Link to comment
Eagle_Adam Posted February 3, 2012 Author Report Share Posted February 3, 2012 Is your thermostat installed facing the correct way (spring towards engine side)? yes, pointy end up spring towards the ground. Checked that on my lunch break just in case i made that mistake :rolleyes: Quote Link to comment
datzenmike Posted February 3, 2012 Report Share Posted February 3, 2012 did this and the block reads 145 and the thermostat housing reads 135 :blink: The new thermostat is defective. Remove and I bet it is stuck open, just replace it. Spend over $10 and get a good one. Quote Link to comment
docbainey Posted February 4, 2012 Report Share Posted February 4, 2012 The new thermostat is defective. Remove and I bet it is stuck open, just replace it. Spend over $10 and get a good one. If you want, take it out and put it in a pan of water on the stove with a kitchen thermometer in it and watch it as you heat it up. If the thermostat opens to early, (cold), the engine will take a long time to warm up. Quote Link to comment
datzenmike Posted February 5, 2012 Report Share Posted February 5, 2012 I find that your time is too valuable. If you find it's no good you have to buy one anyway, if good it's the same amount of work and a new gasket. If I suspect the thermostat I just get a new one... there's no guarantee a new one is perfect and will work out of the box. Quote Link to comment
ggzilla Posted February 5, 2012 Report Share Posted February 5, 2012 You find that eagle_adam's time is too valuable? And even though there is no guarantee a new one is good, you recommended getting a new one and not testing it? I find the pot of water method is very valuable as a learning experience. Quote Link to comment
Eagle_Adam Posted February 6, 2012 Author Report Share Posted February 6, 2012 I find that your time is too valuable. If you find it's no good you have to buy one anyway, if good it's the same amount of work and a new gasket. If I suspect the thermostat I just get a new one... there's no guarantee a new one is perfect and will work out of the box. loz - my time is in short supply but i doubt its valuable :P You find that eagle_adam's time is too valuable? And even though there is no guarantee a new one is good, you recommended getting a new one and not testing it? I find the pot of water method is very valuable as a learning experience. I did test the new one before installation and everything was good to go. The truck is back up to normal operating temp now :D - now i need to find a new petcock to replace the one i sheered off yesterday <_< Quote Link to comment
Lee R Posted February 6, 2012 Report Share Posted February 6, 2012 Re-title your ride as "Mystery Machine" and call it a day. :P Quote Link to comment
ggzilla Posted February 7, 2012 Report Share Posted February 7, 2012 The truck is back up to normal operating temp now How did you fix it? Did you replace the thermostat for the third time and finally got a good one? Quote Link to comment
Eagle_Adam Posted February 7, 2012 Author Report Share Posted February 7, 2012 How did you fix it? Did you replace the thermostat for the third time and finally got a good one? ya, the original was bad, and the first replacement was stuck open when i took it out. The last one i asked for the best one they had which was only a few bucks more and now its good to go. Waiting on a new petcock drain plug and then the cooling system will be up to par :D Quote Link to comment
Eagle_Adam Posted February 9, 2012 Author Report Share Posted February 9, 2012 OK, soooooo NEW issue :rolleyes:. Last night i got the new petcock drain plugs in to replace the one that sheered off in my original endeavor into the cooling system. I got the old one out and drained the cooling system no prob. The issue now is it wont heat up to operating temp again. Difference is this time the upper and lower hose are soft like there is no coolant in them :blink:. The water pump is good (by feel) and im not sure how to "prime" (if that's even close to the right terminology) the cooling system to get fluid back up to the water pump. What did i goof up guys? Quote Link to comment
]2eDeYe Posted February 9, 2012 Report Share Posted February 9, 2012 Sounds like you have air trapped in the system. I usually just run the motor for a bit and keep topping it off until it won't take anymore. Or you could get one of these http://www.denlorstools.com/home/dt1/page_12749_36/lisle_lis24610_spill_free_radiator_funnel_kit_wext.html Or one of these, but you have to plumb it into the system, which I don't like. http://www.prestone.com/products/print/461?popup=1 Quote Link to comment
Eagle_Adam Posted February 9, 2012 Author Report Share Posted February 9, 2012 2eDeYe' date='09 February 2012 - 10:28 AM' timestamp='1328812105' post='630433']Sounds like you have air trapped in the system. I usually just run the motor for a bit and keep topping it off until it won't take anymore. I figured air was the problem, i ran the motor for 10 min or so and the hoses are still soft. How long should it take to work the air out of the system? Quote Link to comment
DanielC Posted February 9, 2012 Report Share Posted February 9, 2012 Did the thermostat have a tiny hole in it, to allow air to bleed past it when filling the cooling system? Make sure the heater valve is also turned on when filling the cooling system. If you did not have the hole in the thermostat, one solution is to get the engine warm, so the thermostat opens, and then the air can get past it. Or remove the thermostat, and drill a small (1/16) hole in the plate. Quote Link to comment
Eagle_Adam Posted February 9, 2012 Author Report Share Posted February 9, 2012 Did the thermostat have a tiny hole in it, to allow air to bleed past it when filling the cooling system? the thermostat did have a small hole with what looked to be a "brass pin" in it - like this one vvv Make sure the heater valve is also turned on when filling the cooling system. not sure what the heater was set at but that makes sense - good to know for future reference Quote Link to comment
]2eDeYe Posted February 9, 2012 Report Share Posted February 9, 2012 How long should it take to work the air out of the system? As said above long enough to get the motor up to operating temp. :) Quote Link to comment
Eagle_Adam Posted February 10, 2012 Author Report Share Posted February 10, 2012 i used my lunch break to run around and see if i could get the air out of the system. A 20 min drive around downtown and the hoses are still soft <_< Guess i shall see how the drive home goes Quote Link to comment
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