Discovery 2 super odd temp issue in -10 degree weather

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tylerw

Member
Mar 17, 2021
6
0
Kansas City
Hi all. I know this topic has been discussed at nauseam but I have tried to search here and google with every phrase I can think of and nothing. So forgive me if this has been discussed.

2002 Disco II. Total engine rebuild including block pressure tested, inline stat mod, new radiator, and water pump. Temps have been great since then. Running about 188-200 plus or minus in the summer according to OBD2 gauge. Gauge would show a little spike after start up and then stat opens and everything settled down.

Fast forward to this week. -10 weather and dash gauge, which I have never seen move above middle, creeps above middle towards 3/4 mark. Odd I think in weather like this. Coolant level is perfect and engine shows no signs of running hot. Parked it for 5 minutes and gauge returns to middle. Go home and get OBD2 gauge. This is when things get weird. Drive it and temps start to climb hitting 242 at one point. 1 min later as I am trying to pull over temps immediately drop to 165-170 range within like 30 seconds. 5 minutes later temps climb again and I check engine. I can wrap my hands around upper hose. Warm but definitely not hot. I use a IR thermometer and point at various places on engine. Highest reading I get right where sensor is was 165 degrees. I conclude I am getting false readings and keep driving. The same process happens again in 5 min or so intervals every time I have tested it. Temps climb from 170 to 242+ stay there for 1 min and drop back down to 17-ish within 30 seconds. Never do the high temps stay high. Again can touch hoses and stat housing which is metal without getting burned. Was even able to open reservoir cap without coolant boiling over or spurting out when gauge read 230 degrees.

I replaced temp sensor and same issue only slightly different numbers. Reached 240 and let truck sit for 5 min. Gauge says 170 when I start it back up and idled at 170 for 20 min until starting to drive again and then creeped up to 230 which was when I was able to open cap with no issues. Also hoses are not rock hard but firm and squeezable when at high temps which seems normal to my recollection. I find it hard to believe these engines can cool down and heat up that fast. Never have I seen that happen so the odds of the stat malfunctioning seems slim.

Any thoughts? Did the extreme cold mess with the ECU? Does the ecu control the temp gauge in vehicle as well? What could I be missing? Anyone else deal with this before? Is it truly overheating?

I appreciate any help in advance.
 
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robertf

Well-known member
Jan 22, 2006
4,795
364
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was the reservoir full? Ive had it happen to a d1, I think it was low on coolant
 
Howski

Howski

Well-known member
Oct 19, 2009
1,498
212
Alabama
X2 on partially frozen coolant causing the t stat not to open when it should. Similar situation happened to me years ago. Not nearly as cold here but now I’m second guessing my own coolant mix…
 
T

tylerw

Member
Mar 17, 2021
6
0
Kansas City
Howski said:
X2 on partially frozen coolant causing the t stat not to open when it should. Similar situation happened to me years ago. Not nearly as cold here but now I’m second guessing my own coolant mix…
Click to expand...
I see your point on the stat but once the engine warms up wouldn't the stat work properly and not still cycle the extreme range?
 
Jimmy

Jimmy

Well-known member
Apr 10, 2006
743
64
Aurora, CO
Air pocket around the temp sensor during the really hot moments? I was in the frozen coolant camp, but wanted to offer another thought.
 
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LRDONE

LRDONE

Well-known member
Dec 3, 2020
340
119
Michigan
Not on my rover but... About 10 years ago I had an 03 audi a4 that did this. Super cold snap we had here in michigan, negative temps. The car would start to over heat while driving and come back to operating temp at idle or when I slowed down. What I found to be the problem was the radiator and coolant freezing up. I temporarily blocked the radiator for the cold snap and that solved all my issues.
 
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kris812

kris812

Well-known member
Jun 11, 2014
267
94
Tucson AZ
My 2 cents, that thermostat is bad.. At those temps the thermostat should be fluttering open and closed as the rad temps are very cold.

70/30 mix I think gives the best freezing abilities as well as heat dissipation. It is possible that water kept getting added and mix is getting low and freezing. Or is pure antifreeze not mixed, which does freeze at 0f to -5f.
 
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tylerw

Member
Mar 17, 2021
6
0
Kansas City
Okay got an update. LRDONE hit the nail on the head I think. I replaced the sensor with no change. Then I pulled the 180 degree in line stat and did a test boiling it on the stove to see how it reacts. It opened perfectly fine so I put it all back together and bled the system best i could. Drove it and still had spiking/cycling issues. Last night I decided to test the stat again and watch what happens as the water on the stove cooled. Stat opened perfectly. They say they start opening at 180 and then are fully open at 200 or so which mine did. I then watched it as it cooled and the stat was fully closed at 165 or 168 degrees. My deduction was that the inline stat was closing and opening in a cycle causing the spikes on the OBD2 digital gauge as well as the vehicle temp gauge. With the stat not in the block I think it cooled to much in this super cold weather causing it to close then engine heated up and stat opened and temps dropped immediately starting the cycle over. Today I blocked the radiator with cardboard as a test and all seems to have settled out.

At first I got one spike at the start of the drive then everything settled down like it should. I drove in the city for 30 minutes after that and temp stayed at 177-179 or so the entire time. Which is low but I know from my test that the stat was still open. Then I went for a highway test at 70mph for about 20 min or so. Temp went up to 188 and then dropped back down to 179 or 177 once back in the city. So it appears the inline stat mod is great for summer but maybe not so much in the winter. Mined needed to keep that coolant warm enough so as to not close the stat.

Glad it was easy at least and glad i know more about how a stat works exactly.

My question though is why not just install a 160 degree stat? Seems like it would solve this issue in the winter as well as help in the summer by starting to open sooner than a 180 or 190 stat. Any reason that is a bad idea?

Thanks for all the help on this.
 
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discostew

Well-known member
Sep 14, 2010
7,735
1,026
Northern Illinois
tylerw said:
I see your point on the stat but once the engine warms up wouldn't the stat work properly and not still cycle the extreme range?
Click to expand...
These stats sometimes let cold coolant get to the sensing bulb aNed cause the stat to not open. Maybe your stat is doing that a little and in the extreme cold it’s an issue
 
Howski

Howski

Well-known member
Oct 19, 2009
1,498
212
Alabama
Since you have an in-line setup did you by chance drill a small hole in the t stat? That generally aids in getting the stat open from my experience by letting a bit of the hot coolant through. May help lessen the wild temp swings. You will suffer lack of HVAC heat with a 160 stat and can’t imagine the engine will be happy running that cold
 
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JohnB

Well-known member
Oct 18, 2007
2,295
12
Oregon
Get the most expensive Stat you can get. There are a tons of options. I'm out of the D2 ownership anymore but I in fact did run a 160 and it kept it at a constant 180 with the inline mod. Didn't cause any Fuel map issues.
Since rover pissed on these things to make a 50 year old motor run for modern emissions a little colder and a little more richness is probably a good thing.

Don't listen to the purist mechanics they live in a paradox of perfection that rover has never presented in any part of their build quality.

And double check that fan clutch.
 
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