The mystery of the overheating D1

H

Haywood

Member
May 10, 2016
8
0
San Diego
The mystery of the overheating D1- SOLVED

I've read through lots of threads already here about similar issues and symptoms to what I'm experiencing, but I just haven't been able to solve mine yet and I'm about out of ideas.
Hoping someone might be able to help me out.

1998 Discovery 4.0 V8, 185k miles. New to me, unknown history.
Seems to run around town at about 200-210. I just noticed that on a long uphill drive that the temp started to climb past halfway on the gauge , my Torque app on my phone said it was hitting 230 and climbing so I pulled over and let it cool. I popped the hood and the coolant was boiling in the expansion tank and venting out the cap.

So far I have replaced a few things and there has been no change.

New, out of the box items installed this weekend-
Radiator
Water Pump
Viscous fan clutch
Thermostat, 160 degree
New serpentine belt.

So tonight I started it from cold and let it idle about 30 minutes in the driveway. Temp finally got to about 192, and I took off for a drive. On the freeway for a few minutes and the temp seemed to stabilize about 185. Then when coming off the freeway the temp got to about 206. By the time I got back to the house and let it idle again it was about 215 and climbing steadily.

I believe I have the air bled out a much a possible. No white smoke from the exhaust. The upper hose is very hot to the touch but not extremely hard with pressure. I also verified that the belt is routed properly, and my a/c fans are working fine. They even kick on without the a/c when it's too hot.
So I've ordered a block test kit to make sure there is no exhaust in my coolant. But other than the possibility of a HG problem, I'm pretty much out of ideas. I really expected my new radiator to be the silver bullet and it wasn't.
I appreciate any more ideas from the pros out there, thanks!
 
Last edited:
p m

p m

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Staff member
Apr 19, 2004
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You may be lucky and find your silver bullet - but judging by what you wrote, the truck has a long history of "deferred maintenance." Meaning it's been running hot for years - and the chance of it having a blown or nearly-blown head gasket or cracked block is not small.

BTW, I'd start with replacing the thermostat with at least 180F, or stock 195F one.
 
H

Haywood

Member
May 10, 2016
8
0
San Diego
p m said:
the chance of it having a blown or nearly-blown head gasket or cracked block is not small
Click to expand...

I understand. I did a block test tonight and I was happy (and surprised) to see that it didn't detect anything. So the search continues..

thumb


thumb
 
kcabpilot

kcabpilot

Well-known member
Mar 26, 2006
334
1
California
Well I'm right along with you Haywood, see my thread on diagnosing overheat on D2. I too have a new radiator, new thermostat and new pressure cap that I'm going to install this weekend. I also have a block tester. My truck started doing the same thing, overheats when going up a hill but will idle and drive around town all day.

From all the research I've done over the past week it sure looks like a cracked block but I have to try all of the preliminaries first. If I do end up having to rebuild my motor I would want a new radiator anyway so that's not a problem. Getting a new block however, that might be a challenge.
 
4Runner

4Runner

Well-known member
May 24, 2007
663
111
Boise Idaho
So let's assume that all your new parts are good. I don't know off hand if this can be done, but is your fan on the clutch the right way? Is the serpent. Belt routed the right way around the water pump? What is the condition of the belt tensioner? Does the temp drop when you have the heat on high? Is it blowing very hot? Are we sure the temp sensor is still accurate? I ran a 160 thermostats in my D1's and it was always too cold. 180 is where you want to be with everything on the up and up. Just some thought at the bottom of a couple of shots of rum. Hope it helps. Good luck
 
D

discostew

Well-known member
Sep 14, 2010
7,735
1,026
Northern Illinois
Take a picture of your belt. So we can see how you have it routed. It will fit a couple ways. I don't think this is caused by a cracked block if your not loosing coolant. Gems blocks don't seem to have that problem.
 
H

Haywood

Member
May 10, 2016
8
0
San Diego
Yes, confirmed my routing is as shown. Thanks. One other thing I noticed is that my new fan clutch is like peanut butter when cold, and at first start up is noticeably louder for the first minute or two. But when I shut it down from full temp, it is at least the same if not able to spin a bit easier. Shouldn't it almost be lock at full heat? Or do I misunderstand the fan clutch?
Thanks.
 
kcabpilot

kcabpilot

Well-known member
Mar 26, 2006
334
1
California
I just went through the fan clutch thing, that was the first thing I tried, so I did a bunch of reading up on it. The clutch is connected to the shaft by way of these annular grooved chambers that fill with silicon fluid when the bi-metal coil in the front heats up and opens a valve. When the valve closes the fluid is flung out of the chambers by centrifugal force. When you turn the engine off the fluid settles at the bottom so on a cold engine it will feel stiff before you start it and you'll hear the fan for a minute until the fluid gets forced out. So if you shut down and feel it immediately before the fluid settles it will be pretty much free-wheeling.

In normal operation, just cruising down the level highway the fan should not be operating. It's purpose is to engage and move air when you are either idling or crawling along in heavy traffic or on a trail. Sometimes on a steep hill on a hot day it will engage if temps start to rise due to the load on the engine but most of the time it should just free-wheel.
 
WaltNYC

WaltNYC

Well-known member
Mar 3, 2010
710
138
NYC
kcabpilot said:
In normal operation, just cruising down the level highway the fan should not be operating. It's purpose is to engage and move air when you are either idling or crawling along in heavy traffic or on a trail. Sometimes on a steep hill on a hot day it will engage if temps start to rise due to the load on the engine but most of the time it should just free-wheel.
Click to expand...

Of course this all depends on the thermostat within the fan clutch. Whatever that trigger temp is for the clutch to engage, that is when the fan will spin with more force.

One thing I didn't care for about the Torqflo fan clutch was that the thermostat was set too low and the fan roared nearly all the time, even with coolant temps near 180 degrees.
 
KngTgr

KngTgr

Well-known member
May 20, 2005
1,323
14
Fairfax, VA
I just performed a block test, sucked air for nearly five minutes, fluid remained blue, the truck idled for 15 minutes, temperature steady at 192, turned it off, the fan spun freely.
The upper hose feels kinda soft though, I would have thought it should feel harder
 
AfiRover

AfiRover

Well-known member
Jul 5, 2004
934
5
48
RACE CITY INDY IN
ok so this may sound strange and unrelated but it has happened before so bare with me.

what is the voltage the alt is putting out ( not the batt voltage) ??
the relationship from the voltage from the alt has a interesting effect on the stock gauge .
 
p m

p m

Administrator
Staff member
Apr 19, 2004
15,643
867
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La Jolla, CA
www.3rj.org
Marco, you got it all wrong. In a D1, it is green, and if it turns out orange, it's probably time to flush it. Of course, if it started orange...
 
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