Wide temp ranges after inline thermostat mod

fiver49er

Active member
Apr 17, 2023
33
7
North Carolina
This is sort of a follow-up to a thread from August 27 (https://discoweb.org/index.php?threads/coolant-temp.102055/ ). Even though the weather has been getting cooler, my running temps were actually getting higher, but not bad - running 197 - 206, but higher than I'd like, especially since it wasn't in the summer heat. So, decided to go ahead with a little prevention and try to get temps down. Swapped out the water pump I installed last year with a new Flowkooler, installed HD fan clutch, installed new Nissens radiator (replaced all hoses and OEM stat last year), and completed the inline stat mod (with some trial and error on hose length/position) with a 180-degree stat and I did drill one 1/8 hole in flange. Shout out to a particular forum member for giving me some helpful tips!

I put coolant in through the top hose (at stat housing connection point) then topped off in reservoir. After letting it idle to operating temp, took it for a test drive (I'll share the full story about this initial test drive and my new concern next, but one issue at time). Wild swings in temp 177 - 206. Got back, burped it, topped off in reservoir drove again. Let it cool overnight and topped off again before test driving. Same thing. Let it cool, topped off a bit more. Later in the day, drove it to a friend's house ~20 miles and started out with wide swings, but eventually settled in between 188 - 194 (mostly highway) and thought OK, maybe it's resolved. However, coming back I had big swings again. Not so much when constantly moving on the highway (although more than on the trip down), but anytime slowed down for traffic or stopped at a light, the temp would shoot up. It got to 216 at one stop light and I quickly put it in neutral and revved it.

I feel like I bled the system pretty well. Any ideas on what's causing the wide swings?

OK, now for the rest of the story related to my initial test drive. Again, idling, the temps were going back and forth, but fine. For the first 1/2 mile or so, same thing, temps going back and forth, but fine. Then temp started going up fast and wasn't coming down. When hit 236, I immediately switched off the ignition. Like an idiot, I had forgotten to tighten the hose clamp where the top hose connects to the radiator and had blown my coolant and left a long trail on the street. Walked home, got my screwdriver and some coolant so I could get it back. Here's where I get nervous that I may have truly effed things up. Leaving the friend's house last night, I heard a new tapping sound when I started it up. Once the engine warmed up, it went away. I haven't started it yet this morning, but please tell me there could be a number of things causing that tapping sound other than liners...
 

kris812

Well-known member
Jun 11, 2014
428
160
Tucson AZ
Tapping sound, probably a lifter.. Got hot, chunk in oil ended up in lifter... Hopeful guess!

For burping a vacuum tool is the right way to do it. My ghetto way has always been driving up a 45' bank and idling for a bit with some revving with the reservoir the highest. I had problems with the heater core gargling, this method helped me.

Check if both electric fans run with the AC on. They're also backup fans when hot.

And Lastly, sounds like a bad fan clutch over all.. Hopefully.. If not that Nissans rad is clogged or never good enough to start with..
 

fiver49er

Active member
Apr 17, 2023
33
7
North Carolina
Update: You may have been right Kris812. Tapping sound is gone. Whew!

Temps a little more stable today. Still bounced around quite a bit until I'd been driving about 10 mins, then pretty much stayed between 187 - 194. The inline stat mod along with the Flowkooler pump seems to have worked. Thanks to everyone for the suggestions.
 
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Climber1

Member
Jan 23, 2024
15
0
Vancouver,BC
I also installed an inline thermostat on a 2004 Discovery 2. Sounds like you have air in your system. Take your coolant reservoir out of the holder and lift it up above the top of the thermostat and take the cap off. Have someone start the car while you hold the reservoir or support it at a higher elevation. Run the engine at 2000 rpm for 3 minutes, repeat a couple of times. Turn heater controls on high when you are doing this and make sure the coolant level stays topped off. Also did you install the thermostat with hole in 12 o'clock orientation to allow air to escape. I did this on mine and it worked good no air. At this time of the year I run around 180-182 F and in hot weather have not seen it go above 189F.
 

best4x4

Well-known member
Mar 1, 2015
619
90
Beaumont, TX
When I switched to an OEM Grey thermostat on my D2's (way before the inline mod was born) Temps would go to say 193-204F on the highway at speeds, get on a slow street or road and temps would then drop to 180-183, then shoot back up to 193. It was honestly the thermostat going open, closed, open closed, opened, closed, opened, closed... With the inline I had it sitting at 174F around town, get out on the freeway and it would go up to 193F range, but once you weren't accelerating it would creep back down, then if you passed someone it would surge back up to 193F or higher then once you were cruising without much change it would creep back down. The wide range is from having a load on the system so thermostat goes wide open, then as it cools it slowly closes. At least that's what I've come up with.

On my D2's I never had any issues with the OEM LR Grey 180F from the diesels. It was the load of generic so called 180's that were awful... Britpart for a while had a black OEM style which was actually a 178F unit and it was excellent, then like everything good they changed vendors, and the 180's were actually just stock temp units...... People would install them thinking 180F see no change in their temps, and go to town with other parts being replaced with sadly the same temp range only to find out the thermostat was the issue the entire time!

Also in my experience I've seen 99-02 D2's run warmer than 03-04 D2's. The extra oil cooler in front of the radiator adds more heat flow thru the radiator vs the 03-04 which just has the AT cooler vs both an AT cooler/oil cooler like 99-02 D2's. It's not a huge amount, but it all adds up on a hot day.