DIY low coolant warning lamp

lithium1330

Technical Excellence Contributor
My ‘97 Defender 90 didn’t come with any coolant level warning, and it seems the only way is the DIY... so, I assembled the parts and made this setup over the weekend. Now, if my coolant runs low, I get a warning light on the dash. Here is a write up and some pix of what I did...

Parts & tools you'll need (you don't have to get the exact parts, but these are what I used):
  • a float switch. I decided to spend a little more for one from liquidlevel.com (a company in CT). Their floats have published specs...and that's goodness in my book. part#LS-11-051/2. You can also find cheaper ones (w/ mixed reviews) on amazon.
  • Legines Brass Pipe Fitting, Bulkhead Anchor Coupling, Bulkhead Tank Fitting, Frame Nipple, 1/8" NPT Female, 1-1/2" Length (Pack of 2) from amazon.
  • LED bulb size74 part#74-NW from superbrightled
  • 1'x1'x 1/16" silicone sheet to make my own gasket to seal the bulkhead fitting, also from amazon.
  • metric washer (home depot)
  • Step drill bit to drill the reservoir, round file/sandpaper, and some high temp thread seal (ARP or Permantex 59124) to seal the various threads
Steps:
  1. Find your coolant reservoir/overflow tank. In the Defenders, this is a brass unit, and drill a hole big enough to fit the bulkhead fitting (measure twice, drill once). Also, drill it far enough you can still open/close the filler cap after sensor is installed. File/smooth out any sharp edges - you don't want this to cut into the silicone gasket later.
    8241


  2. Fit the float switch into the bulkhead (apply thread sealant) - noted this pic is different than the final assembly I had. After taking this pic, I found float was sitting too high in the tank.
    8242


  3. Make a gasket for the bulkhead for inside the tank, and another gasket for outside the tank (square orange with round cutout in above pic).
  4. Check the float to make sure it has continuity when float is down (low coolant). If not, remove circ clip, flip the float to make it so.
  5. Thread the float wires through the tank - through the fill hole then out the drilled hole. Then, drop the float into the tank and check fitment and as important, float depth/height. Ideally, you want the float to almost touch bottom of the tank. You can make float sit lower in tank by adding the extra bulkhead nut to the bulkhead fitting, then silicone gasket, and also how much you turn the float into bulkhead fitting (step 2).
    8245


    8243


  6. Once the height is good, you can put the other gasket on the outside, put a washer, lock washer then the nut. I put thread sealant between gasket and also at the nut. Tighten things down.
    8244
  7. (Optional) using some shrink tube/rubber grommet to keep the float wires from rubbing against the threads of bulkhead fitting. Test again for continuity by filling up the tank. If all OK, put the tank back in the truck and connect up all hoses.
  8. Run one of the float wires to ground, the other inside the cab where you can wire up the light and 12v source.
  9. For the in-dash warning light - i used the unused coolant warning lamp in the panel (below turn signal). You'll find the socket and just add the LED bulb. Run power from 12v power source when key is in the on-position.
    8246


  10. Once wired up, test it to make sure light is on when no coolant. Then fill reservoir and the warning light should go out. If you set the float low enough in the tank... filling the overflow reservoir a little more than 1/2 way should not trigger false warnings - even when going around turns, up/down hills, etc. Then run the truck, get up to temp and check for leaks. If you did a good job, things should stay bone dry.
    8247
 

Uncle Douglas

Well-known member
Thanks, and it does.
Was wondering about the 97's.

We use the plastic bottle when retrofitting a gems engine like yours into a defender.
On the 94/95 NAS 90's that brass one isnt a reservoir its just an overflow bottle. It doesnt drain back to the lower radiator hose.
With the plastic coolant res you can use the cap with integral sensor that came on some models,
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
This is nice.

What I did was to use a RRC cap from the plastic type tank. However, when the float gets low, it breaks the circuit! In other words, the light is ON when the tank is good, but the light goes OFF when the tank gets too low. I didn't want a light just always on, so I put a button in the circuit as a Push to Test type of thing. I can push the button, and if the light comes on, the level is good. If no light, I know I need to check the level.

Probably not as good as what you made, but it's something, and it can be tested at any time. I had to pull it out to do some other work, and to make it more permanent. But when I get it back installed, I'll take some photos to show off.
 

Red90

Well-known member
This is nice.

What I did was to use a RRC cap from the plastic type tank. However, when the float gets low, it breaks the circuit! In other words, the light is ON when the tank is good, but the light goes OFF when the tank gets too low. I didn't want a light just always on, so I put a button in the circuit as a Push to Test type of thing. I can push the button, and if the light comes on, the level is good. If no light, I know I need to check the level.

Probably not as good as what you made, but it's something, and it can be tested at any time. I had to pull it out to do some other work, and to make it more permanent. But when I get it back installed, I'll take some photos to show off.
You just need a relay to make this work correctly. My suggestion is to have an audible alarm on this as well. It is usually a critical event.
 

lithium1330

Technical Excellence Contributor
I thought about using the tank from RRC (look almost the same), but didn't have all the hose connections/nipples. I was also hoping to find a plastic tank with integrated sender in the cap... but would have required working up custom hoses. <--I assume custom hose runs is what you do when refreshed with plastic tanks?


Was wondering about the 97's.

We use the plastic bottle when retrofitting a gems engine like yours into a defender.
On the 94/95 NAS 90's that brass one isnt a reservoir its just an overflow bottle. It doesnt drain back to the lower radiator hose.
With the plastic coolant res you can use the cap with integral sensor that came on some models,
 

Uncle Douglas

Well-known member
I just buy the lower hose for a 97 NAS 90. The later Classic's, V8 D1, tdi 90, all use the same plastic tanks, either clear or black plastic are available.
Downside is, the plastic tanks have been known to split with age and if you get the clear ones they can get discolered and ugly.
Upside is they are a bit larger and add coolant capacity. The coolant level sender from a classic is built into the cap and screws right on.
 

rocky

Well-known member
D1's in 94/95 had the plastic tank. I reused mine when dropping the V8 into my truck
 

lithium1330

Technical Excellence Contributor
A friend with the plastic tank (D2) burst mid-way through a 5 days trip. It totally sucked. When he opened the hood, water was everywhere in the engine bay - the plastic tank had cracks in multiple places. We trailed patched it with a full roll of silicone tape. I've never had the plastic tank fail in my other more modern cars...but glad the 90 has a metal tank. I did consider one of those aluminum tanks (allisport knock-offs) on ebay. BUt just couldn't find one with right fittings.
 
Top