69 Temp Gauge / Coolant Issue

[Michael C.]

I'm new to NCRS and this forum. Unbelievable amount of info here.

I'm the original owner of a 69 427/390 with < 61K miles. Obviously sat up a lot over the years, but now trying to get it safe and somewhat reliable again.

I haven't trusted the temp reading and found a detail thread that led me to replace the temp sending unit. The new unit is from NAPA (needed something quick). The gauge readings are now more believable, but still appear low. The needle reaches the tick mark between 100 and 210 after about 20 minutes running - parked and 70 deg in shop. I haven't pulled the stat yet. I know it's supposed to be 195 deg, but I might have changed it years ago.

Can anyone tell me what temp the unlabeled tick marks are supposed to indicate? In addition to the unlabeled mark mentioned above, there's another one between 210 and 250.

With a digital thermometer thermocouple lead clamped to the nipple at the intake manifold from the WP I read 160 and the gauge needle is on the first unlabeled tick mark as stated above. At this time I read 103 ohms across the temp sensor. Based on the info provided in the thread I referenced, this "could" be in the ballpark. A post on that thread stated 100 deg = 160 ohm and 210 deg = 72 ohm.

I tested the gauge by removing the sending unit lead and the gauge needle deflects max CCW. When I ground the gauge lead, the needle deflects max CW. I haven't yet tried a fixed resistor as one post suggested to simulate a known temp.

My questions are: value of unlabeled temp gauge marks; might I have a problem with the generic temp sending unit; if gauge is indicating 160 deg, is this too low for 70 deg ambient?

Thanks, Mike

[Dick W.]

Re: 69 Temp Gauge / Coolant Issue

I'm new to NCRS and this forum. Unbelievable amount of info here.

I'm the original owner of a 69 427/390 with < 61K miles. Obviously sat up a lot over the years, but now trying to get it safe and somewhat reliable again.

I haven't trusted the temp reading and found a detail thread that led me to replace the temp sending unit. The new unit is from NAPA (needed something quick). The gauge readings are now more believable, but still appear low. The needle reaches the tick mark between 100 and 210 after about 20 minutes running - parked and 70 deg in shop. I haven't pulled the stat yet. I know it's supposed to be 195 deg, but I might have changed it years ago.

Can anyone tell me what temp the unlabeled tick marks are supposed to indicate? In addition to the unlabeled mark mentioned above, there's another one between 210 and 250.

With a digital thermometer thermocouple lead clamped to the nipple at the intake manifold from the WP I read 160 and the gauge needle is on the first unlabeled tick mark as stated above. At this time I read 103 ohms across the temp sensor. Based on the info provided in the thread I referenced, this "could" be in the ballpark. A post on that thread stated 100 deg = 160 ohm and 210 deg = 72 ohm.

I tested the gauge by removing the sending unit lead and the gauge needle deflects max CCW. When I ground the gauge lead, the needle deflects max CW. I haven't yet tried a fixed resistor as one post suggested to simulate a known temp.

My questions are: value of unlabeled temp gauge marks; might I have a problem with the generic temp sending unit; if gauge is indicating 160 deg, is this too low for 70 deg ambient?

Thanks, Mike

Older Vette instrumentation leaves a lot to be desired. They are indicators not guages. Best way to check is using an IR digital thermometer. Shoot the thermostat housing for a very close reading of water temperature.

[Michael C.]

Re: 69 Temp Gauge / Coolant Issue

Thanks Dick.
I've been looking for an IR thermometer to check for thermal issues in my house, now more justification to get one.

Since initial post I've put the stat and found that it's 160 deg. Must have been changed by the shop that change my rusty freeze plugs. At least I now can trust the thermocouple thermometer. I'll go back with the 195 deg.

[Joe L.]

Re: 69 Temp Gauge / Coolant Issue

Thanks Dick.
I've been looking for an IR thermometer to check for thermal issues in my house, now more justification to get one.

Since initial post I've put the stat and found that it's 160 deg. Must have been changed by the shop that change my rusty freeze plugs. At least I now can trust the thermocouple thermometer. I'll go back with the 195 deg.

Michael-----


I generally recommend stock-specification components. However, not in the case of thermostats for certain applications. Yours is one of those applications. For your application I do not recommend a 160 degree thermostat (I never recommend a 160 degree for any 1963 or later Corvette) but I also don't recommend a 195 degree. I recommend the use of a 180 degree.

[Paul H.]

Re: 69 Temp Gauge / Coolant Issue

The first mark on the gauge between 100 and 210 is 180 degrees. I have a 180 thermostat in my 68 427/390 and that is where it runs. I have confirmed the reading with an IR gun and have discussed this issue with a number of people. The consensus I got from those discussions is that area on the gauge is in fact 180.

[Michael C.]

Re: 69 Temp Gauge / Coolant Issue

Thanks everyone for the info. Off to the parts store to swap the 195 for a 180.