Cool at idle, gauge reads hot when driving?

[68 Greenie]

Ever since I installed my 383 with this 292 cam with .501 lift my factory gauge shows it running hot after just driving down the block. I have a rad cap and it only shows about 150 but my gauge inside just keeps climbing but when I stop to idle it goes down. I have an aluminum radiator with duel cooling fans. I had a temp. ascending unit from and 86 installed in a port in the intake. My motor by the way is a 86 block. I today installed the correct temp. ascending unit for a 68 but I had to put it in the top of the water pump and it still does the same thing. Could it be a bad gauge? I have also been told that my 600 edelbrock performer is not enough carb. and may be running to lean so that might be why my gauge goes up when driving and down at idle. I have never heard this but im not ase certified mechanic either. I need help getting very frustrated and don't want to destroy my new motor. I really appreciate your guys opinions, it helps but this one has thrown me for a loop. Thanks.

[Boog]

It almost sounds like there is no thermostat letting the coolant flow too fast to cool off.

[68 Greenie]

Well I even installed a new thermostat a 180 and it still does the same thing. Im just at a total loss of what to do.

[ElKotze]

When it's getting hotter while driving, in most cases it's because of clogged radiator or radiator too small. Just not enough heat exchange. More than once I have seen this happen with electric fans, sometimes switching back to stock fan clutch setup helps. I don't think it's your timing, it would run hot when idling, too. Same with running lean.

[hjewell2]

Originally Posted by 68 Greenie

Ever since I installed my 383 with this 292 cam with .501 lift my factory gauge shows it running hot after just driving down the block. I have a rad cap and it only shows about 150 but my gauge inside just keeps climbing but when I stop to idle it goes down. I have an aluminum radiator with duel cooling fans. I had a temp. ascending unit from and 86 installed in a port in the intake. My motor by the way is a 86 block. I today installed the correct temp. ascending unit for a 68 but I had to put it in the top of the water pump and it still does the same thing. Could it be a bad gauge? I have also been told that my 600 edelbrock performer is not enough carb. and may be running to lean so that might be why my gauge goes up when driving and down at idle. I have never heard this but im not ase certified mechanic either. I need help getting very frustrated and don't want to destroy my new motor. I really appreciate your guys opinions, it helps but this one has thrown me for a loop. Thanks.

Don't feel bad I have a 1980 Malibu that does the exact same thing, driving me nuts.

[rockyrivermark]

First thing I would do is get an IR gun and get true temp at the T stat housing.
This way you can eliminate sending units and gauges and know for sure if it's actually getting too hot. I picked one up fro Amazon for $15 to check temps on boat exhaust manifolds. I use it for other things and more than I thought I would. Nice to have in the shop anyway.
2nd that noted here with electric fans.
Report back.

[AussieinNC]

New 383...great !

New radiator? 2 core,,,,3 core,,,4 core...?

Electric fans...please check they are truing the correct way...must be pulling air thru radiator if mounted behind....what controls fan turn on and off?

Shrouds?

I usually get best results with factory fan clutch and factory shroud...and no electric fans...

Check the wire running to the gauge...ground out the wire on the engine and power on the ignition...the gauge should read full hot...remove wire from being grounded out...gauge should return to cold...

Is this truck air conditioned?

What exhaust system ? New ?

Post pics of where the sender unit is mounted..

Have fun...

[68 Greenie]

I have a new 3 core champion aluminum rad. with 2 11inch cooling fans. The gauge worked great with my old stock motor but i had the temp unit in the head. These old school 202 heads don't have that so I have had it in the intake and now in the top of the water pump both doing the same thing. All I have is the green wire hooked to the ascending unit. Should there be another wire and if so where? I have looked on the back of the gauge cluster and cannot find anything on the back of the temp gauge. FRUSTRATED?

[Boog]

There is only one green wire going to the temp sending unit.

[AussieinNC]

Only one wire is needed for the temp sender...should be green if I remember correctly.

Grab yourself an aftermarket capillary style temp gauge and fit it into the manifold port...

Give the truck a run and compare the results...I suspect the gauge in the dash may be faulty...

The best place for the temp switch is in that manifold port when running the older heads...

[Steeveedee]

Go and put your hand near the top radiator hose and feel how hot it is. Maybe even lay a hand on it, just for a moment. If it doesn't feel that hot, something from your gauge or the sender or wiring is messed up. I installed a mechanical temperature gauge in my truck after getting temperature readings like this. I'm thinking that it's the gauge or maybe the printed circuit, but for now, I had a "free" temp gauge after I sold my Skylark GS, so I installed it in my truck.

[Boog]

If you don't have a threaded hole in the intake manifold you can buy a thermostat housing with a threaded hole in it. I currently have one of those on mine. And it's chrome by the way.

[68 Greenie]

Im wondering if it just isn't the gauge or the printed circuit either. Aussie do you mean ground out the sending unit wire to something then turn the switch on and it should go hot then unhook it and it should go back to cold? It has new vintage air but its doing this without even having it running. I have ram horn dual exhaust 2.5 inch. The thing that is weird with all of this is that the gauge worked perfect with my ole stock motor. Still frustrated. Thanks for the help guys keep it coming I'll get it figured out sometime.

[Ontcalimo]

I had similar problem with my old Cadillac when I used an aftermarket temp sending unit. I the bought an OEM one, and the problem was solved.

[Mr Handy]

I sounds like to me the wrong temp sender. new sender and old gauge read hot. i went through 3 senders from the parts store before I dug out the original and installed it. The original gauge runs at a different resistance. There is a company that is making the correct sender but I can't remember their name for the life of me.

when you pop the hood when it is reading hot on the gauge, does it really feel hot? can you touch the hose? is is the rad hot? there is a big difference between 180* and 230* when you pop the hood in my experience.

[Andy4639]

Originally Posted by 68 Greenie

I have a new 3 core champion aluminum rad. with 2 11inch cooling fans. The gauge worked great with my old stock motor but i had the temp unit in the head. These old school 202 heads don't have that so I have had it in the intake and now in the top of the water pump both doing the same thing. All I have is the green wire hooked to the ascending unit. Should there be another wire and if so where? I have looked on the back of the gauge cluster and cannot find anything on the back of the temp gauge. FRUSTRATED?

How many CFM are the fans each?

For cooling:
Rule of thumb.

Cooling.

1,250 CFM for a 4-cylinder
2,000 CFM for a 6-cylinder
2,500 CFM for a 8-cylinder

[AussieinNC]

Re: Aussie do you mean ground out the sending unit wire to something then turn the switch on and it should go hot then unhook it and it should go back to cold?

Yes, exactly...

[68 Greenie]

Okay Aussie I will try that. I can't remember the cfm's on the fan but the aluminum rad and the fans are brand new also. I'll try Aussie's plan first and go from there. The factory gauge inside just keeps climbing but my buddy had one of those IR guns and its only reading about 160 on the thermo housing. I don't know very confusing. I'll check my cfm's on fans when I get a chance.

[HO455]

Originally Posted by Mr Handy

I sounds like to me the wrong temp sender. new sender and old gauge read hot. i went through 3 senders from the parts store before I dug out the original and installed it. The original gauge runs at a different resistance. There is a company that is making the correct sender but I can't remember their name for the life of me.

when you pop the hood when it is reading hot on the gauge, does it really feel hot? can you touch the hose? is is the rad hot? there is a big difference between 180* and 230* when you pop the hood in my experience.

Second this. My new sender worked fine under 165* then would short to ground and peg the guage high. I will look and see if I can find the number for you.

[custom10nut]

Have you checked to see if you're running Lean on the Carb? A Lean condition at higher RPM will cause your problem too.

[Ontcalimo]

I still think you have an incompatible sending unit. I had this issue with mine.

[68 Greenie]

Well I'm running a Edelbrock 600 performer right now but I'm getting ready to buy a new Edelbrock 750. Hopefully that will help with being to lean.

[68 Greenie]

Okay Ho455 thanks. Is there a compatible sender that's a 3/8 instead of the factory 1/2?

[HO455]

I am not aware of any. I believe everyone either drills and taps the intake to 1/2" NPT or gets their sender modified. There is a member who does the modification if you need. Here is a link.

http://67-72chevytrucks.com/vboard/s....php?p=3293657

You can test the sender if you have a multimeter.

[Steeveedee]

Originally Posted by 68 Greenie

Well I'm running a Edelbrock 600 performer right now but I'm getting ready to buy a new Edelbrock 750. Hopefully that will help with being to lean.

A bigger carb won't help a lean condition, it depends on the jetting. You can buy a kit from E-brock that has metering jets and rods, and springs for the metering rods. I got rid of my E-brock carb and went back to a Q-Jet on my Buick; it runs way better. I never removed the Q-Jet from my truck except to rebuild it.