D1 Fan clutches

1of40

Well-known member
Oct 23, 2017
244
58
Va
Question for the experienced crowd. My factory stock reservoir cap says 9lb psi, whereas a new cap I recently purchased says 15lb psi. Which one would you run?

Note this is a NAS defender with the small metal res tank cap, that the D1 plastic tank/cap combo.
 

p m

Administrator
Staff member
Apr 19, 2004
15,617
838
58
La Jolla, CA
www.3rj.org
Interesting point.
I found here that "Using a pressurized radiator cap can raise the system pressure and thus the coolant boiling point. A typical 1 Bar (14.5psi) pressure cap theoretically raises the boiling point of 50-50 coolant to 253°F."
You really don't want to be near 253°F.
 

1of40

Well-known member
Oct 23, 2017
244
58
Va
Interesting point.
I found here that "Using a pressurized radiator cap can raise the system pressure and thus the coolant boiling point. A typical 1 Bar (14.5psi) pressure cap theoretically raises the boiling point of 50-50 coolant to 253°F."
You really don't want to be near 253°F.
That’s my thinking as well. 15psi, assuming it doesn’t cause any other leaks should in theory help keep the temps down more so than 9psi.
 

p m

Administrator
Staff member
Apr 19, 2004
15,617
838
58
La Jolla, CA
www.3rj.org
That’s my thinking as well. 15psi, assuming it doesn’t cause any other leaks should in theory help keep the temps down more so than 9psi.
Sorry if I wasn't clear.
That's exactly against my thinking. A 15-psi cap will not keep the temps down any more than a 9-psi cap, but it would allow the engine running hotter without losing coolant - until the heater core blows up.
 
  • Like
Reactions: 1of40 and WaltNYC

jymmiejamz

Well-known member
Dec 5, 2004
6,008
361
35
Los Angeles, Ca
Just had my wife’s D1 run hot for the first time after idling for 10 minutes in near 100F weather. Hopefully Ron Davis Radiators makes a replacement for the D1 like they do for Defenders.
 

WaltNYC

Well-known member
Mar 3, 2010
707
135
NYC
Just had my wife’s D1 run hot for the first time after idling for 10 minutes in near 100F weather. Hopefully Ron Davis Radiators makes a replacement for the D1 like they do for Defenders.
That is a pretty extreme case but one that we encounter in traffic entering/exiting the city from time to time (not to mention the LI Expressway). A Hayden 2991 helps in these cases.
I enquired about the radiator at Ron Davis and am waiting for a response.
 

p m

Administrator
Staff member
Apr 19, 2004
15,617
838
58
La Jolla, CA
www.3rj.org
That is a pretty extreme case but one that we encounter in traffic entering/exiting the city from time to time (not to mention the LI Expressway). A Hayden 2991 helps in these cases.
I enquired about the radiator at Ron Davis and am waiting for a response.
I have to say that a few of my Rovers have cheap aluminum radiators - which seem to work much better than original copper/brass units.
Of course, you get what you pay for - one I inherited with the truck, and the bottom radiator hose port was bolted to the plastic tank. There was no O-ring or any kind of sealant between the plastic tank or port - so it was dripping a little all the time. When I finally got to it and sealed it well, it hasn't shown a drop.

This is to say that Allisport or Ron Davis or whatever exotic place makes good stuff, but you don't have to wait for months to sort out your cooling problems.
 

Tugela

Well-known member
May 21, 2007
4,754
562
Seattle
Not having the full service history of my D1, I replaced much of the cooling system as a pre-emptive measure: water pump, fan clutch, hoses, radiator, and thermostat. My local indie Rover shop persuaded me to buy a Nissens aluminum-plastic radiator and since installing it my coolant temperature readings stay in the 189-194 F range. On occasion they'll go a couple degrees higher in certain conditions but drop quickly. Granted, I changed several components at once so I can't isolate the effect of any single part but I also can't complain about the results.

I'm not sure what to expect from this radiator in terms of lifespan. It's been five years of reliable performance so far. I did recently get my hands on an all-aluminum, 4-row radiator that I plan to install at my next scheduled coolant replacement interval.
 

jymmiejamz

Well-known member
Dec 5, 2004
6,008
361
35
Los Angeles, Ca
I’ve been down this road enough times with defenders that I’m going to go with what I know definitely works. My wife’s d1 has one of those aftermarket fan clutches that is locked up 90% of the time. I’m done with that.
 

discostew

Well-known member
Sep 14, 2010
7,706
1,015
Northern Illinois
I’ve been down this road enough times with defenders that I’m going to go with what I know definitely works. My wife’s d1 has one of those aftermarket fan clutches that is locked up 90% of the time. I’m done with that.
Find some old guy who knows how to re core the thing. If you know anybody who restores old muscle cars they should know who does it in your area.
 

jymmiejamz

Well-known member
Dec 5, 2004
6,008
361
35
Los Angeles, Ca
Been down that road too, haha. The radiator shop here sucks. I had a good one in LA. The one here has given me a radiator back that leaked like a sieve.
 

outono

Well-known member
Sep 26, 2020
162
85
Orange, CA
The Ron Davis radiator for D1's is $1,586 and has a 4-5 week lead time. It has 2 rows of 1 inch tubes and includes both oil and transmission coolers.
Render below (sent by Ron Davis).

1-64DI96.jpg

That's a lot of coin, but if you've got it then I don't think you can do better.

For most, Nissens is going to be just fine...
 
Last edited:
  • Like
Reactions: p m

terryjm1

Well-known member
Jan 23, 2011
1,486
375
Hayden have been good in mine. Amazon carries some. The 2991 really screams in the D1

View attachment 62536
Any reason not to try the 2781? It would seem to be less extreme than the 2991, sort of a happy medium?

Also, something I find interesting, Haden shows the 2991 as the equivalent to the stock D2 fan. If you search the 2991 part number at Rock Auto, it lists only 2 OEM part numbers as its equivalent, both are stock D2 numbers - ERR4959, ERR4996.

Was a severe duty clutch standard on a D2?
 
Last edited:

robertf

Well-known member
Jan 22, 2006
4,780
355
-
Ordered a potluck fan clutch off amazon

this truck has a 4 core brass radiator, flowkooler pump, and the most unloved 4.0 that still runs. yesterday it hit 97F. Put about 100 miles on it and truck holds 180ish at speed, climbs to upper 190s-205ish at long stop lights
 
  • Like
Reactions: terryjm1

terryjm1

Well-known member
Jan 23, 2011
1,486
375
This D1 has a factory original radiator with 27,000 ish miles, new flowkooler water pump, and a factory 56,000 ish mile fan clutch. It’s only gotten hot when going up a long incline with the AC on. The AC doesn’t get real cold at low engine rpm and when driving slow in general. I’m only going by the factory gauge but will plug in my scanner to monitor it until this is corrected. When it gets hot (3/4 but still in the so called normal range) if I stop for 5-10 minutes with the engine running it cools back down, both electric fans operating seemingly well.

What temperature do the fans come on and go off without the AC running?
 

terryjm1

Well-known member
Jan 23, 2011
1,486
375
Just went for a test drive with the scanner hooked up. It made it to 215 and the gauge barely moved off its usual mark. Makes me nervous about how hot it was a 3/4 on the dash gauge. My previous experience tells me the radiator is likely the issue. It doesn’t really heat up until under load for a while with the AC running. As soon as i coast for a bit it drops right down. The next trip back from the desert should be revealing.
 
Last edited:

terryjm1

Well-known member
Jan 23, 2011
1,486
375
Ordered a potluck fan clutch off amazon

this truck has a 4 core brass radiator, flowkooler pump, and the most unloved 4.0 that still runs. yesterday it hit 97F. Put about 100 miles on it and truck holds 180ish at speed, climbs to upper 190s-205ish at long stop lights
Mind sharing which pot luck fan clutch you purchased?