graysmoke

Recently purchased a 91 305. Ive notice the temp sits at about 1/3 on the gauge when driving around town even with ac on. I read the thermostat might be stuck open (fail safe or removed). To test I started the car cold with the radiator cap off and saw the coolant moving. I then noticed my heater hose that goes from the radiator to heater has been bypassed to go from radiator to manifold. I think this is the coolant I am seeing moving, not sure. Also felt the top radiator hose after 5 mins idling and it got warm to hot. is this bypass path okay. I dont want to change anything making something run worst. any advice.

Keoman

iTrader: (3)

Post up some pictures of this coolant bypass you are talking about.
Only real way to know its stuck is to take it out and look at it.

graysmoke

Here's a photo. The bypass was done by the previous owner using a prestone flush adaptor. My concern is the heater core was bypassed but not like what I have read in the tech forum. I got a new 195 thermostat but havent installed it yet.

Keoman

iTrader: (3)

I see, so he bypassed the heater core completely.
Turning the inline valve to the closed position should interrupt the coolant flow and have some effect on how the temperature behaves.
If it were me, id reconnect the heater core but I have to wonder why they did that. Only reason I can think of is the heater core is leaking and they didn't want to go through the hassle of changing it.

PS
Thanks for the arrows!

graysmoke

I was thinking of running a garden water hose to one side of the core, cap off the other side and opening full pressure. think this would work to test if it leaks.

graysmoke

I put off the heater core to focus on the original issue of always running cold. The gauge was always around ~160 thinking the thermostat was open. Also the previous owner had wired the fan to stay on by grounding the fan switch wire. I think this might have added to the running cold problem. So today I pulled out the thermostat. It looked new, it was shut, said 192 so I tested it, boiled it and it opened fine so I reused it. I replaced fan switch with part# TFS4 and reconnected it. Also new upper rad hose. Added new coolant and worked the air out. Now its running hot 220-240 and fan doesnt come on til 240 and turn off when its back to 220. what could cause it to run much hotter?

Keoman

iTrader: (3)

This is a very common question among TGO members, I myself have asked the exact same question.
Have a good read through this, it's amazing how they designed the car to run.
https://www.thirdgen.org/forums/cool....html?styleid=

Given the above link, I changed my fan switch and was fortunate enough to figure out how to burn my own PROM chips so that I could control my fans to work in harmony with my 180* thermostat. Best combination I can come up with:

180* thermostat: ac delco part numbrer 10220957 (good luck finding a 180, 170's alot more common)
Standard Motor Products fan switch: Part Number TS85 (new connector part number 85140)
Custom PROM tune: On @ 200* Off @ 185*

graysmoke

Keoman - thanks for the info. From what I read the TS85 closes at 211. I think my new fan switch is bad. fan is turning on at 240 and the switch specs says closes 211 To 227 degrees. Tested my temp sender and gauge using resistors (here) and its within 5 degrees of whats showing. Also confirmed my readings from a cold idle by feel of the upper rad hose thermostat opening at 195 and temp gauge showing that temp drop. I'm going to have change it out again which sucks.

graysmoke

Final fix - My coolant fan switch was bad not turning on at the stated temp range. So rather than going through a possible bad switch ordeal again or trial and error of these fixed temp fan switches I decided to go with an adjustable fan switch Hayden # 3653 , $17 orielys. This is a basic adj on/off probe. The probe mounts along the upper radiator not through it or in it. The unit has two connections that forms a switch just like the stock fan switch. I wired it one side to ground and the other to the fan relay ground. I made adjustments and now I run a constant 200 degree range. Lesson - no more coolant in the eye.

Keoman

iTrader: (3)

Sorry to hear you got a bad switch, that's really odd. Mine works on the money stays right around 210 on a hot day when both fans kick on however my gauge reads what I would estimate to be 225* when the secondary fan turns on.
Only sure fire way to check the temperature on your block is with an laser thermometer. If you want to double check your gauge, stop by the local checker, oreiley or autozone and most of them carry laser temp guns. Aim at a freeze plug if possible to get the most accurate reading. Taking the temp at the intake manifold will yield false temperature results.

graysmoke

thanks, I think Ill try that next time I go by there but im good now. This is what I used to check it and at 220 that switch still wasnt kicking on till it was in the 240 red.