G20 overcooling?

[Ole Sparky]

Hi,

I just finished a top end rebuild on my mom's 88 G20 3/4 ton vandura (5.7 TBI). It runs great, except for two possibly related problems:

1. The temperature needle never gets above 1/4, although the heater does get nice and hot, as does the upper rad hose.

I installed a new 180 deg thermostat during the rebuild, as per my local parts store's recommendation, as well as a new water pump.

2. The surge tank is ALWAYS low. It simply always gets down to 3 inches or so below the "cold fill" line when cold, and an inch above the line when hot. It does not appear to be "burning" coolant (no white smoke, compression is ~160 in all cylinders, clean coolant). It's a real head-scratcher. So far I am trying a new radiator cap, as the gasket looks a little tweaked.

Thanks very much in advance for your help.

Edit: I wanted to add that the PO installed an aftermarket Hayden plate-and-fin transmission cooler in front of the AC condenser. They completely bypassed the stock one. I am 99% sure that this has nothing to do with the overcooling, but too much info is better than too little.

[DFBonnett]

Originally Posted by Ole Sparky

Hi,


1. The temperature needle never gets above 1/4, although the heater does get nice and hot, as does the upper rad hose.

I installed a new 180 deg thermostat during the rebuild, as per my local parts store's recommendation, as well as a new water pump.

The OEM spec for your stat is 195 deg according to the Stant catalog. You may want to switch it out and see if that helps.

[Ole Sparky]

I added a 195. No change. The engine is getting to the correct temp. This leads me to believe that the problem is either in the coolant temp sensor or the gauge itself. I know how to test the CTS. Is there any way to test the gauge?

Thanks in advance,
Joe

[Ole Sparky]

fixed tank level problem - had hairline crack. superglued shut until further notice.

[Shrewz92]

What's the test for the coolant temp sensor? I don't know that.