Thermostat/cooling system help needed (1 Viewer)

[jlhollowx13]

Hi all, I am in need of some insight from those that know the workings of the cooling system better than me.

What I have: 1987 fj60 with 90s SBC.

My issue: the engine temp goes up to about 3/4 or closer to redlining in the initial heat up of the engine. Once the engine hits the 3/4ish mark it begins to cool down. After that it seems to run too cold. The temp guage reads about 1/4 maybe up to half after the initial warm up. I live in a very cold place during this time of the year so my heat isn't that great with the engine seeming to be running cooler than it should. My guage and radiator are stock fj60 parts.

My assumption is my thermostat may not be the correct temp or it is sticking or something. I am wondering what you all think might be going on here. I plan to replace the thermostat, but I am not sure what temperature thermostat I should go with. Winters here are very cold, usually not getting above freezing during the winter months, somewhere between the negatives Ferenheit up to freezing. Summer time we might see 80s once in awhile, but I also want to make sure ill be good on trips to hotter climates.

I'm not sure if my thermostat is too cold, too hot or what, so any help is very much appreciated!

 

[OldTrailFab]

I'm assuming this is a new problem and hasn't existed since the engine swap right?

It sounds like you're thermostat is sticking, if you're fuel injected, get a new OEM thermostat and I bet you'll be all set. If you're carbureted, you can probably pick how warm you want it to run. I don't know what the operating temp should be for your engine, but many newer motors are running in the 210* range, where as older motors were typically 180*. So you're stock gauge might need to read a little high for the 350 to be happy.

 

[jlhollowx13]

I'm assuming this is a new problem and hasn't existed since the engine swap right?

It sounds like you're thermostat is sticking, if you're fuel injected, get a new OEM thermostat and I bet you'll be all set. If you're carbureted, you can probably pick how warm you want it to run. I don't know what the operating temp should be for your engine, but many newer motors are running in the 210* range, where as older motors were typically 180*. So you're stock gauge might need to read a little high for the 350 to be happy.

I bought the rig with the swap and it has been that way since I've had it. The engine i believe is TBI. I'm thinking maybe the thermostat is sticking as well since it takes a higher temp to make it open, but once it opens it seems to stay open. I am pretty sure my engine is an early 90s but I haven't had luck confirming the exact year. Id assume they all ran about the same temp though.

 

[OldTrailFab]

yeah, regardless of whether your gauge reads dead center or not, it should warm up to operating temp, then stay there with a functioning thermostat. I would personally just run a stock one, but I don't know if there is some other advantage to running something higher or lower(I've never lived anywhere quite as chilly as Gunnison). You should be able to find the VIN on your block and confirm the application pretty easily with a little help from google, or just pull that thermostat out and bench test it. Almost every auto part store is going to have that in stock, and its cheap! Good luck!

 

[jlhollowx13]

Just thought I would post an update. I replaced my thermostat and have been driving it for a couple of days. I'm still having the same behavior with the temperature. I put in a 195 degree thermostat which is what the auto parts store was showing was oem recommended. Also the one I pulled out was 195 degree. Not real sure what is going on here. I put a temp gun to the engine and checked things out and I didn't see any temps that seemed too high anywhere on the engine. The highest I would see was a little over 200 near the thermostat. I am considering getting an aftermarket temp guage with number readouts to install that way I can monitor things more accurately, at least that way I will know if I'm getting too hot, but I don't think I am. Its just an annoying thing to me to see the temp spike then drop like it does and not know whats going on. If anyone has any ideas I'm happy to hear them! Thanks!

 

[OldTrailFab]

I read a few threads about this on here, tons of info about tons of different setups and peoples results. Sounds like your TBI wouldn't care if you ran a cooler thermostat, which I doubt is your issue but could be part of it. Your temp gauge could be pulling from the head which will read 15* or so hotter than at the thermostat, this seems like maybe it makes the most sense to me. Lots of fan related possibilities too, what do you have for fans?

 

[haryv]

Hi all, I am in need of some insight from those that know the workings of the cooling system better than me.

What I have: 1987 fj60 with 90s SBC.

My issue: the engine temp goes up to about 3/4 or closer to redlining in the initial heat up of the engine. Once the engine hits the 3/4ish mark it begins to cool down. After that it seems to run too cold. The temp guage reads about 1/4 maybe up to half after the initial warm up. I live in a very cold place during this time of the year so my heat isn't that great with the engine seeming to be running cooler than it should. My guage and radiator are stock fj60 parts.

My assumption is my thermostat may not be the correct temp or it is sticking or something. I am wondering what you all think might be going on here. I plan to replace the thermostat, but I am not sure what temperature thermostat I should go with. Winters here are very cold, usually not getting above freezing during the winter months, somewhere between the negatives Ferenheit up to freezing. Summer time we might see 80s once in awhile, but I also want to make sure ill be good on trips to hotter climates.

I'm not sure if my thermostat is too cold, too hot or what, so any help is very much appreciated!

Okay here's a few things you need to do. Put your hand around the radiator hose does it feel hot? That means the water is flowing into the radiator and exiting back into the engine. If you want to see if there's any cold spots or hotspots on the radiator and if you have access to the front of the radiator I put your hand on the radiator head start feeling for any cold spots. If the radiator feels very hot then it's doing its job. If it's cold then the thermostat is not opening up or it's not opening up enough. Too bad you didn't have a thermal infrared gun to test the temperature on the radiator. Have you open up the cooling system in introduced air into the cooling system? If so Jack the truck up on jacks and then bleed the air out of the cooling system.

 

[jlhollowx13]

Okay here's a few things you need to do. Put your hand around the radiator hose does it feel hot? That means the water is flowing into the radiator and exiting back into the engine. If you want to see if there's any cold spots or hotspots on the radiator and if you have access to the front of the radiator I put your hand on the radiator head start feeling for any cold spots. If the radiator feels very hot then it's doing its job. If it's cold then the thermostat is not opening up or it's not opening up enough. Too bad you didn't have a thermal infrared gun to test the temperature on the radiator. Have you open up the cooling system in introduced air into the cooling system? If so Jack the truck up on jacks and then bleed the air out of the cooling system.

Thanks for the input, I do have an infared thermometer which I used and saw a high temp around 200 degrees at the thermostat. I checked in random spots on the engine block and radiator as well as the radiator hoses and it seemed like coolant was moving through the system based on the Temps. I also bled the system, let it run to operating temp with the radiator cap off then let it run an additional half hour after it go to operating temp with the heaters blasting while topping it off as needed. That was done on Sunday and I have driven it every day since. The first day it did suck a little coolant out of the overflow reservoir but since then my overflow res has been the same so it appears the system has been bled properly. The fact that it still spikes, then drops down to the proper range on the guage with the new thermostat just doesn't make sense. I'm starting to wonder if the new thermostat is also sticking?

I read a few threads about this on here, tons of info about tons of different setups and peoples results. Sounds like your TBI wouldn't care if you ran a cooler thermostat, which I doubt is your issue but could be part of it. Your temp gauge could be pulling from the head which will read 15* or so hotter than at the thermostat, this seems like maybe it makes the most sense to me. Lots of fan related possibilities too, what do you have for fans?

My temp sensor is right next to the thermostat on the front center of the engine. I hadn't thought about the fan, but its the stock (as far as I know) 350 fan on the motor. Maybe the clutch on the fan isn't working properly? Another thing to check.

I am wondering on the compatibility of the 350 sensor with the fj60 guage. Maybe there is an issue there. I have a blank space in the old radio slot after relocating the radio to a locking console and was considering putting some guages there. I will also do some more temperature measurements with the infared gun to see what things look like at the time of the spike vs normal.

 

[OldTrailFab]

maybe the fan...still seems like the if everything else is functioning correctly your temp should cycle back up as the thermostat tries to regulate it. I wouldn't worry too much about extra gauges, once you get it sorted out it, the gauge may not read dead in the center, but it should always be at about the same spot once you are at your operating temperature. I don't think more gauges will help diagnose this problem.

If you drive it long enough to spike, then cool off, then park it and leave it run, what happens to the temps?

 

[jlhollowx13]

maybe the fan...still seems like the if everything else is functioning correctly your temp should cycle back up as the thermostat tries to regulate it. I wouldn't worry too much about extra gauges, once you get it sorted out it, the gauge may not read dead in the center, but it should always be at about the same spot once you are at your operating temperature. I don't think more gauges will help diagnose this problem.

If you drive it long enough to spike, then cool off, then park it and leave it run, what happens to the temps?

After it spikes it will drop down and stay there for as long as I drive it or let it run and doesn't fluctuate. It has to sit and cool off completely before I see the spike again, usually the next morning.

 

[OldTrailFab]

weird

 

[haryv]

Thanks for the input, I do have an infared thermometer which I used and saw a high temp around 200 degrees at the thermostat. I checked in random spots on the engine block and radiator as well as the radiator hoses and it seemed like coolant was moving through the system based on the Temps. I also bled the system, let it run to operating temp with the radiator cap off then let it run an additional half hour after it go to operating temp with the heaters blasting while topping it off as needed. That was done on Sunday and I have driven it every day since. The first day it did suck a little coolant out of the overflow reservoir but since then my overflow res has been the same so it appears the system has been bled properly. The fact that it still spikes, then drops down to the proper range on the guage with the new thermostat just doesn't make sense. I'm starting to wonder if the new thermostat is also sticking?


My temp sensor is right next to the thermostat on the front center of the engine. I hadn't thought about the fan, but its the stock (as far as I know) 350 fan on the motor. Maybe the clutch on the fan isn't working properly? Another thing to check.

I am wondering on the compatibility of the 350 sensor with the fj60 guage. Maybe there is an issue there. I have a blank space in the old radio slot after relocating the radio to a locking console and was considering putting some guages there. I will also do some more temperature measurements with the infared gun to see what things look like at the time of the spike vs normal.

heat from heater core?

 

[jlhollowx13]

heat from heater core?

Yep, getting heat from both front and rear heaters. I warmed up the truck today so I could move it for snow removal. Let it fully warm up and drove it around a little. I took temp readings and even when the temp guage was showing 3/4ish I was seeing about 180 to 190 degrees at the most around the temp sensor/thermostat area on the top of the engine, saw about 160 to 170 at the radiator where the coolant comes in at the top. On the block near the exhaust I was seeing about 230 at the peak, but not sure how accurate it was with the exhaust being there and it being a bit of a tight space. Ill do some more checking when I drive it next.

 

[haryv]

Engines were never designed to be redundant. It's too bad though. Tomorrow's Vehicles will be electric so gas engines will disappear. Have you no longer have to deal with a lot of the problems with today's engines. I just read on to it as website that they've come up with a solid-state battery I know that will allow the owner of the vehicle to church there vehicle within 10 minutes

 

[RAYJON]

Just a thought check the wiring for the coolant sensor, sounds like the motor is doing what it should, my next guess is the sensor or wiring, a grounding of the sensor wire would cause the spike you are talking about, the sensor could also be going out and getting weird... good luck...