Cooling system help
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Teching In
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Cooling system help Looking for some validation here as I’m having trouble. My 98 Z28 recent cracked a radiator.
i replaced the radiator and flushed the cooling system while I was at it. While driving the car with coolant and flush solution, the car started boiling out of the overflow tank, with the gauge around 210.
i flushed and refilled with coolant, and now at idle car goes up to the 210 mark, fans never kick on. I tried forcing them on with the AC, but they didn’t come on them either. Unfortunately prior to this the AC wasn’t blowing cold so there is something wrong with that system, so not sure ignoring my fan issue is related or not. For reference prior to this in 2 years I have never seen the temp gauge get to 210, ever.
i have check the fan relays, and the wiring to the relay box. 12v everywhere, from in front and behind the harness connector on passenger side to the box itself.
Also ran power direct to the fans and fans and they work fine.
So my questions are:
Is there any other way to force the fans on?
What could cause me boiling over at such a low temp?
Anybody have the instructions for making a fan switch? (The threads I searched had dead links.)
Any help is appreciated!
i replaced the radiator and flushed the cooling system while I was at it. While driving the car with coolant and flush solution, the car started boiling out of the overflow tank, with the gauge around 210.
i flushed and refilled with coolant, and now at idle car goes up to the 210 mark, fans never kick on. I tried forcing them on with the AC, but they didn’t come on them either. Unfortunately prior to this the AC wasn’t blowing cold so there is something wrong with that system, so not sure ignoring my fan issue is related or not. For reference prior to this in 2 years I have never seen the temp gauge get to 210, ever.
i have check the fan relays, and the wiring to the relay box. 12v everywhere, from in front and behind the harness connector on passenger side to the box itself.
Also ran power direct to the fans and fans and they work fine.
So my questions are:
Is there any other way to force the fans on?
What could cause me boiling over at such a low temp?
Anybody have the instructions for making a fan switch? (The threads I searched had dead links.)
Any help is appreciated!
Please add your location to your profile so we can see where you are coming from. It makes a difference, particularly in heating/cooling issues like this. We have site members in the Arab States, Scandanavia, Alaska, Florida, etc. The cars behave differently in those extremes...
You have a '98, so the temp gauge is different than the later years. You see a true temperature reading at the sensor.
Lot's of problems with the install:
- Blown fuse
- Cut wire or mis-connected wiring connector
- Bad/broken fan relay
- Hoses hooked up wrong to radiator (main cooling hoses OR the small vent/overflow hoses)
- Bad or mis-installed thermostat
- Bad temp sensor
- Bad radiator cap
- Anything about the system that is non-stock (if there are attributes like this, we need to know)
Had you not mentioned anything about the fans, I would have gone to the cap, hoses and thermostat first. Those are the most common things.
More food for thought: Your temp sensor senses temperature at one point in the system. The boil-over and pressure could be happening at another point. If your temp sensor isn't reading or showing you 210 degrees, the fans aren't going to be triggered on. Diagramming out the system flow (coolant and vents) may help figuring things out.
Is the coolant flowing out of the reservoir hot and steaming?
If you have a new radiator and "new" pressure cap and that cap doesn't pressurize the system correctly, it could flow straight to the overflow as the system heats up. Putting your old cap on, could change things. Did you change the radiator design with this replacement?
Lot's of problems with the install:
- Blown fuse
- Cut wire or mis-connected wiring connector
- Bad/broken fan relay
- Hoses hooked up wrong to radiator (main cooling hoses OR the small vent/overflow hoses)
- Bad or mis-installed thermostat
- Bad temp sensor
- Bad radiator cap
- Anything about the system that is non-stock (if there are attributes like this, we need to know)
Had you not mentioned anything about the fans, I would have gone to the cap, hoses and thermostat first. Those are the most common things.
More food for thought: Your temp sensor senses temperature at one point in the system. The boil-over and pressure could be happening at another point. If your temp sensor isn't reading or showing you 210 degrees, the fans aren't going to be triggered on. Diagramming out the system flow (coolant and vents) may help figuring things out.
Is the coolant flowing out of the reservoir hot and steaming?
If you have a new radiator and "new" pressure cap and that cap doesn't pressurize the system correctly, it could flow straight to the overflow as the system heats up. Putting your old cap on, could change things. Did you change the radiator design with this replacement?
Thread Starter
Teching In
Joined: Sep 2018
Posts: 7
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Please add your location to your profile so we can see where you are coming from. It makes a difference, particularly in heating/cooling issues like this. We have site members in the Arab States, Scandanavia, Alaska, Florida, etc. The cars behave differently in those extremes...
I will add to profile, however I am in Reno NV. On the day I experienced overheating temps were in the 80’s. On the day the original rad cracked, temps were in the 90’s.
You have a '98, so the temp gauge is different than the later years. You see a true temperature reading at the sensor.
Lot's of problems with the install:
- Blown fuse
Checked the 10amp fuse for fans, still working correctly
- Cut wire or mis-connected wiring connector
Only wire no longer used is the coolant level sensor, all other wires look good
- Bad/broken fan relay
All fan relays have continuity when energized, and each was swapped with the starter relay as an additional test
- Hoses hooked up wrong to radiator (main cooling hoses OR the small vent/overflow hoses)
Hoses are installed correctly
- Bad or mis-installed thermostat
Did not take thermostat out but with cap off once car reaches temp thermostat flows correctly back into radiator
- Bad temp sensor
Unplugged this and fans did not come on
- Bad radiator cap
Stock radiator cap, original
- Anything about the system that is non-stock (if there are attributes like this, we need to know)
Only non original equipment in the cooling system is the radiator.
I did have trouble getting air out when refilling, so I eventually re-flushed and filled directly into the top hose until it came back to the radiator. Then filled as normal.
Had you not mentioned anything about the fans, I would have gone to the cap, hoses and thermostat first. Those are the most common things.
More food for thought: Your temp sensor senses temperature at one point in the system. The boil-over and pressure could be happening at another point. If your temp sensor isn't reading or showing you 210 degrees, the fans aren't going to be triggered on. Diagramming out the system flow (coolant and vents) may help figuring things out.
Is the coolant flowing out of the reservoir hot and steaming?
Yes, it was steaming and boiled out.
If you have a new radiator and "new" pressure cap and that cap doesn't pressurize the system correctly, it could flow straight to the overflow as the system heats up. Putting your old cap on, could change things. Did you change the radiator design with this replacement?
No, stock replacement spectra cu1485. I did not replace the cap, still using old.
I will add to profile, however I am in Reno NV. On the day I experienced overheating temps were in the 80’s. On the day the original rad cracked, temps were in the 90’s.
You have a '98, so the temp gauge is different than the later years. You see a true temperature reading at the sensor.
Lot's of problems with the install:
- Blown fuse
Checked the 10amp fuse for fans, still working correctly
- Cut wire or mis-connected wiring connector
Only wire no longer used is the coolant level sensor, all other wires look good
- Bad/broken fan relay
All fan relays have continuity when energized, and each was swapped with the starter relay as an additional test
- Hoses hooked up wrong to radiator (main cooling hoses OR the small vent/overflow hoses)
Hoses are installed correctly
- Bad or mis-installed thermostat
Did not take thermostat out but with cap off once car reaches temp thermostat flows correctly back into radiator
- Bad temp sensor
Unplugged this and fans did not come on
- Bad radiator cap
Stock radiator cap, original
- Anything about the system that is non-stock (if there are attributes like this, we need to know)
Only non original equipment in the cooling system is the radiator.
I did have trouble getting air out when refilling, so I eventually re-flushed and filled directly into the top hose until it came back to the radiator. Then filled as normal.
Had you not mentioned anything about the fans, I would have gone to the cap, hoses and thermostat first. Those are the most common things.
More food for thought: Your temp sensor senses temperature at one point in the system. The boil-over and pressure could be happening at another point. If your temp sensor isn't reading or showing you 210 degrees, the fans aren't going to be triggered on. Diagramming out the system flow (coolant and vents) may help figuring things out.
Is the coolant flowing out of the reservoir hot and steaming?
Yes, it was steaming and boiled out.
If you have a new radiator and "new" pressure cap and that cap doesn't pressurize the system correctly, it could flow straight to the overflow as the system heats up. Putting your old cap on, could change things. Did you change the radiator design with this replacement?
No, stock replacement spectra cu1485. I did not replace the cap, still using old.
Something above can't be right. It's really hard for fluid not too far above 210 to over-pressure (ie: boil-over) unless lines are hooked up wrong or the pressure cap is bad or there is an unexpected additional source of pressure. (Other than normal heating.)
The other possibility could be that you have another source of pressure in the system, like a blown head gasket. (That source of pressure could be what did in your last radiator.) You might do a pressure test of the system.
The other possibility could be that you have another source of pressure in the system, like a blown head gasket. (That source of pressure could be what did in your last radiator.) You might do a pressure test of the system.
Thread Starter
Teching In
Joined: Sep 2018
Posts: 7
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Something above can't be right. It's really hard for fluid not too far above 210 to over-pressure (ie: boil-over) unless lines are hooked up wrong or the pressure cap is bad or there is an unexpected additional source of pressure. (Other than normal heating.)
The other possibility could be that you have another source of pressure in the system, like a blown head gasket. (That source of pressure could be what did in your last radiator.) You might do a pressure test of the system.
The other possibility could be that you have another source of pressure in the system, like a blown head gasket. (That source of pressure could be what did in your last radiator.) You might do a pressure test of the system.
I am thinking that the first time I flushed I may have had air because I just filled from the radiator before someone gave me the advice to fill from the top hose into the engine first.
Also given when the fans kicked on, I believe my coolant is actually around 230 when I see 210 on the gauge.
Last, I am wondering if the pcm was controlling the fans perfectly the whole time, or if the pcm was failing to ground the fan relay but the new switch is successfully providing ground when it gets the signal from the pcm. I don’t know enough about these switches.
No. Any air in the system collects in the top of the radiator and then gently burps/vents out as the car heats up and comes up to temperature and pressure. In order for fluid to flow to the overflow bottle, there has to be an open pathway (through the radiator cap) of normal pressure or a flow of excess pressure.
The PCM will only trigger the fans to come on when it reads a high temperature from the coolant sensor. It sounds like you have a pressure problem that the system is experiencing before the system comes up to temperature.
You may just have a bad radiator cap or it could have been damaged during the swap, or it may not be on correctly. (The arrows on the cap must be pointed so they are aligned with the hoses.)
I would start with a pressure test of the system. You should be able to rent the pressure tester from a local auto parts store for free. If you hold pressure - then the next step would be to try a new cap. If you get a cap, be sure to get a bone-fide GM cap. Lots of folks have had issues with the aftermarket caps. (Nothing will sink you to the depths of hell like chasing a cap issue with the wrong new part...)
The PCM will only trigger the fans to come on when it reads a high temperature from the coolant sensor. It sounds like you have a pressure problem that the system is experiencing before the system comes up to temperature.
You may just have a bad radiator cap or it could have been damaged during the swap, or it may not be on correctly. (The arrows on the cap must be pointed so they are aligned with the hoses.)
I would start with a pressure test of the system. You should be able to rent the pressure tester from a local auto parts store for free. If you hold pressure - then the next step would be to try a new cap. If you get a cap, be sure to get a bone-fide GM cap. Lots of folks have had issues with the aftermarket caps. (Nothing will sink you to the depths of hell like chasing a cap issue with the wrong new part...)
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Thread Starter
Teching In
Joined: Sep 2018
Posts: 7
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No. Any air in the system collects in the top of the radiator and then gently burps/vents out as the car heats up and comes up to temperature and pressure. In order for fluid to flow to the overflow bottle, there has to be an open pathway (through the radiator cap) of normal pressure or a flow of excess pressure.
The PCM will only trigger the fans to come on when it reads a high temperature from the coolant sensor. It sounds like you have a pressure problem that the system is experiencing before the system comes up to temperature.
You may just have a bad radiator cap or it could have been damaged during the swap, or it may not be on correctly. (The arrows on the cap must be pointed so they are aligned with the hoses.)
I would start with a pressure test of the system. You should be able to rent the pressure tester from a local auto parts store for free. If you hold pressure - then the next step would be to try a new cap. If you get a cap, be sure to get a bone-fide GM cap. Lots of folks have had issues with the aftermarket caps. (Nothing will sink you to the depths of hell like chasing a cap issue with the wrong new part...)
The PCM will only trigger the fans to come on when it reads a high temperature from the coolant sensor. It sounds like you have a pressure problem that the system is experiencing before the system comes up to temperature.
You may just have a bad radiator cap or it could have been damaged during the swap, or it may not be on correctly. (The arrows on the cap must be pointed so they are aligned with the hoses.)
I would start with a pressure test of the system. You should be able to rent the pressure tester from a local auto parts store for free. If you hold pressure - then the next step would be to try a new cap. If you get a cap, be sure to get a bone-fide GM cap. Lots of folks have had issues with the aftermarket caps. (Nothing will sink you to the depths of hell like chasing a cap issue with the wrong new part...)
Thanks for your wisdom, hopefully a documentation of my stupidity will help someone else.
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Please add your location to your profile so we can see where you are coming from. It makes a difference, particularly in heating/cooling issues like this. We have site members in the Arab States, Scandanavia, Alaska, Florida, etc. The cars behave differently in those extremes...
You have a '98, so the temp gauge is different than the later years. You see a true temperature reading at the sensor.
Lot's of problems with the install:
- Blown fuse
- Cut wire or mis-connected wiring connector
- Bad/broken fan relay
- Hoses hooked up wrong to radiator (main cooling hoses OR the small vent/overflow hoses)
- Bad or mis-installed thermostat
- Bad temp sensor
- Bad radiator cap
- Anything about the system that is non-stock (if there are attributes like this, we need to know)
Had you not mentioned anything about the fans, I would have gone to the cap, hoses and thermostat first. Those are the most common things.
More food for thought: Your temp sensor senses temperature at one point in the system. The boil-over and pressure could be happening at another point. If your temp sensor isn't reading or showing you 210 degrees, the fans aren't going to be triggered on. Diagramming out the system flow (coolant and vents) may help figuring things out.
Is the coolant flowing out of the reservoir hot and steaming?
If you have a new radiator and "new" pressure cap and that cap doesn't pressurize the system correctly, it could flow straight to the overflow as the system heats up. Putting your old cap on, could change things. Did you change the radiator design with this replacement?
You have a '98, so the temp gauge is different than the later years. You see a true temperature reading at the sensor.
Lot's of problems with the install:
- Blown fuse
- Cut wire or mis-connected wiring connector
- Bad/broken fan relay
- Hoses hooked up wrong to radiator (main cooling hoses OR the small vent/overflow hoses)
- Bad or mis-installed thermostat
- Bad temp sensor
- Bad radiator cap
- Anything about the system that is non-stock (if there are attributes like this, we need to know)
Had you not mentioned anything about the fans, I would have gone to the cap, hoses and thermostat first. Those are the most common things.
More food for thought: Your temp sensor senses temperature at one point in the system. The boil-over and pressure could be happening at another point. If your temp sensor isn't reading or showing you 210 degrees, the fans aren't going to be triggered on. Diagramming out the system flow (coolant and vents) may help figuring things out.
Is the coolant flowing out of the reservoir hot and steaming?
If you have a new radiator and "new" pressure cap and that cap doesn't pressurize the system correctly, it could flow straight to the overflow as the system heats up. Putting your old cap on, could change things. Did you change the radiator design with this replacement?
Looking for some validation here as I’m having trouble. My 98 Z28 recent cracked a radiator.
i replaced the radiator and flushed the cooling system while I was at it. While driving the car with coolant and flush solution, the car started boiling out of the overflow tank, with the gauge around 210.
i flushed and refilled with coolant, and now at idle car goes up to the 210 mark, fans never kick on. I tried forcing them on with the AC, but they didn’t come on them either. Unfortunately prior to this the AC wasn’t blowing cold so there is something wrong with that system, so not sure ignoring my fan issue is related or not. For reference prior to this in 2 years I have never seen the temp gauge get to 210, ever.
i have check the fan relays, and the wiring to the relay box. 12v everywhere, from in front and behind the harness connector on passenger side to the box itself.
Also ran power direct to the fans and fans and they work fine.
So my questions are:
Is there any other way to force the fans on?
What could cause me boiling over at such a low temp?
Anybody have the instructions for making a fan switch? (The threads I searched had dead links.)
Any help is appreciated!
i replaced the radiator and flushed the cooling system while I was at it. While driving the car with coolant and flush solution, the car started boiling out of the overflow tank, with the gauge around 210.
i flushed and refilled with coolant, and now at idle car goes up to the 210 mark, fans never kick on. I tried forcing them on with the AC, but they didn’t come on them either. Unfortunately prior to this the AC wasn’t blowing cold so there is something wrong with that system, so not sure ignoring my fan issue is related or not. For reference prior to this in 2 years I have never seen the temp gauge get to 210, ever.
i have check the fan relays, and the wiring to the relay box. 12v everywhere, from in front and behind the harness connector on passenger side to the box itself.
Also ran power direct to the fans and fans and they work fine.
So my questions are:
Is there any other way to force the fans on?
What could cause me boiling over at such a low temp?
Anybody have the instructions for making a fan switch? (The threads I searched had dead links.)
Any help is appreciated!
Last edited by 98LS1auto; Sep 25, 2019 at 10:58 PM.
Thread Starter
Teching In
Joined: Sep 2018
Posts: 7
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Buy a Hi/Lo fan switch from Summit and wire it up. You can run them on hi or low whenever you want. Mine sits in the glove box. I only use it at the track between runs when I want to cool it down quicker. Do not trust that cluster gauge. You need to hook up a scanner that is checking the data stream in real time. It will give the accurate coolant temp.
Well wssix99, you were correct in your original post. This was 100% my fault, I had swapped the small vent hoses around when re-installing. After swapping these the temperatures are running exactly the same, but am no longer getting the boiling sound under the radiator cap when I shut the engine off. I found this when I was going to pressure test, I guess that is what I get for rechecking my work late at night after having already broken into the whisky. Since I was there I completed the pressure test and everything checks out normal.
The vent line port is a part of the pressurized system and when it's hooked up to the overflow, that opens the entire pressurized system (bypassing the radiator/pressure cap) to the air. The system doesn't pressurize, the water boils right at 212 degrees, (The pressurized system raises the boiling point.) and the fluid can escape to the bottle.
I'm glad you are running again!
Joined: Nov 2001
Posts: 34,629
Likes: 2,550
From: Schiller Park, ILL Member: #317
The '98 gauge isn't perfect but I wouldn't say that it sucks, at least not compared to the newer ones. Mine is also off by about ~15 degrees, but it actually moves around as the coolant temp changes. On the other hand, the '99-'02 version really does suck - those always show either a hair under or a hair over "210" for anything in the 185-235°F range. At least the '98 gauge moves around within that range, showing an actual change in coolant temp rather than a fixed number for a ~60°F range.
I've owned my '98 since it was new and I griped to the dealer when it was under warranty about this, and they adjusted the needle on the gauge. I recently did this again a few weeks ago because it was off again, but there had been numerous engines and sensors replaced in those 20 years, so hard to say what caused it to start reading off again. when I had the cluster out. I set it to read 235 on the gauge when it was 235 in the scanner. When it cooled down, it was still within a few degrees at 210, depending upon whether I leaned slightly left to look straight at the gauge. I don't like the 99-02 dummy gauges.