Looking for some help here. I have a 95 and the issues with the fans is unlike anything I have read. Sometimes when I start the engine. The secondary fan will come on after a few minutes and run at high speed while the primary never comes on. Secondly there are times that when the engine temp reaches 185 both fans will come on at low speed. Once the temp get's to 205 the primary fan shuts off and the secondary runs at high speed. I let the tem reach about 240 and the primary never comes back on. Force testing the fans they both work normal. Any idea's out there that might guide me in the right direction?

 

I have a 95 also. So first let's talk about how the fans are supposed to work. BUT before we do let's make sure that when you are talking about temps you are not referring to the analog gauge ..... the car does not use the output from that sensor located on the passenger side for anything at all. The computer utilizes the data from the temp sensor located at the front of the engine right by the water pump. This sensor provides the digital temp and thus it is the digital reading that you should judge everything by.

Per the 95 FSM the two cooling fans work together. (there is not a primary or a secondary fan) When the digital temps reach approx 228F BOTH fans come on at the low speed setting. After a 5 degree drop in temp they turn off. When the digital temp reaches approx 237F both fans come on at the high speed setting. After a 5 degree drop they revert to the low speed setting. When you turn on the AC both fans come on by default at the high speed setting. There are 3 relays that control the two cooling fans they are mounted on the drivers side of the radiator shroud.

It is possible that a previous owner has had the programming in the computer modified to control the fans in a different way. It's also possible that one of the relays is not functioning properly.

As a side note .... once the vehicle reaches approx 30-35 mph the fans turn off regardless of the temps because at that road speed the air flows through a properly functioning (clean) system faster than the fans can pull the air through the radiator.

 

I did look t the analog gauge but was reading off the OBD scan tool. Both were reading the same temp. The coolant sensor in the front of the engine for the fans was recently replaced. The three relays were also replaced. Wires were traced back to the PCM and were good. No abrasions or breaks. The drivers side fan will turn off but the passenger goes into high speed. Engine temp was at 255 before I shut the engine off. The next day at 185 degrees both fans came on low speed. once the temps got to 22o the drivers fan turned off and the passenger fan went into high speed. Very possible the previous owner had the settings changed but I have no history. One thing to mention. this all started after the engine was built to a 383. ECM / PCM have not been tuned but I wouldn't think that could be the whole issue going on. neither fan will turn on when the a/c is turned on but the a/c get's cold so that is working. is there a way to check the water pump to assure it is working properly?. I am going to replace the PCM to see if anything changes.
Thanks for the feedback.

 

When the water pump get tired and start malfunctioning it will drip coolant from the weep hole under the pump and over the optispark

 

Is it possible to get the wires in the relays out of position? If so, can you verify that the wires in the relays are in their proper positions?

 

The wires in the connectors are molded and cannot be taken out without some good effort. Is there a good schematic of the wire pinouts anywhere that I can reference? Relays will only go into there prospective sockets one way.
And on the water pump. Is it possible that the impeller is not functions properly? Just looking for possibilities.

 

Water pump not pumping?.... POSSIBLE.....but pretty unlikely. That one is easy to diagnose:
1. Warm up car...does the heater blow hot heat? If so...water pump pretty much has to be pumping water through the heater core....right?
2. Warm car up until the stat opens (over 190*F), then monitor engine temps digitally, then quick go measure radiator temps (w/a temp gun, for example). If the radiator is the same temp as the engine...pump has to be working, right?

 

Very true and the heater does get hot.

 

Copy. Your water is circulating, then.

 

Has anyone heard of the PCM possibly malfunctioning and cause issues with the fans cooling?

 

the water pump is driven directly by the camshaft, if the cam turn the pump the impeller turn.

 

He knows his pump is working, at this point. I think that he is (rightly) focusing on the fans, at this point.

 

True, I'm just trying to find out why they work so inconsistently at different times. But thanks for all the feedback. Anytime I take it out for a drive the temperature runs away and I have to pull over and let it cool. these a very short trips. less than three miles.

 

What temperature are you seeing at highway speed, like at 65-70mph? It won't help figuring out your fans on/off issue, but I would pull the radiator and clean out the cores cooling fins, also hose out the AC condenser as well. As stated above, once moving faster than 30+mph the engine should cool without fans, if it doesn't, the condenser and radiator are likely plugged up (sticky on this). Is your air-damn in place? Perhaps you've already taken care of this, but if your car is moving and still overheating, you may have more issues than just the fans. Lastly, how about the thermostat? Correct one for an LT1? Good luck👍

 

While driving the temp continues to rise. I have seen it go as high as 255 before I stop. The radiator and a/c condenser both were blown out. Coolant is very clean. Yes the air damn is in place. Looking at the analog oil gauge it runs around 200+. The thermostat was replaced with a 185 sense that's where it use to run before the engine was built. Would the timing be a possible cause? I do smell raw gas when idling. enough to burn your eyes. How can the timing be adjusted on the lt1 or checked? What should the timing advance be on a stroker motor with a high performance crane cam? I do not know the cam spec's because when the engine was built I had the builder use the same cam.

 

Just because the thermostat was replaced doesn't mean its good.

I changed mine and it made it about 10 minutes before it got stuck open. Had to change it again.

 

It's possible that it is open. No way to tell without removing it.

 

Just to be clear, all heater hoses, cross-over steam pipe that connects to the back of heads, etc are intact? Timing should all be handled electronically, you definitely should have a custom tune performed. Running rich should cause a "cooler" condition, running lean is when things get hot enough to melt holes in pistons! Aside from the fan issue, something else is not right if the radiator is clean and it still overheats at speed!!! Oil looks OK, no chocolate milk? I will ponder some more! I brought up the thermostat, because many times people have mistakingly installed a traditional SBC thermostat instead of the "dual stage" SBC2 lt1 thermostat!👍

 

I just noticed you referred to the "analog oil gauge" are you going off of oil temp or coolant temp!? It's not uncommon for oil temp to get to 255°+!👍

 

Temp is checked with OBD scan. Not sure about the heater hoses. How should they be routed? Just threw the oil temp out there. The thermostat is a standard one picked up from Orileys auto parts.