KZJ78 temp probe in upper hose?

[kgrove]

Has anyone mounted a coolant temp probe in the upper hose of a KZJ78? It's a relatively short hose with two bend, so I haven't been able to come up with a good solution that allows the hose to match up and provide a solid clamping zone. The only thing I can think of is having somebody fabricate a bent section of hard tubing and then weld a probe bung on the curved section. I'd love to see images of how anyone here has been able to fab a hose together that your happy with.

For reference, here's an image of the upper hose next to a somewhat standard temperature probe adaptor. The hose needs roughly 1-1.5" of straight section at either end to confidently clamp on to the radiator and engine outlet, and then the metal probe housing is a little over 2.5" of straight section itself. There isn't much room to achieve the correct bend by the time you incorporate those straight sections. I've tried allowing some bent sections to attach to the probe housing, but it really doesn't allow for a solid joint... I'd be afraid of developing coolant leaks over time.

 

[AVL KZJ78]

I tried a similar hose adapter and I too was not happy with it- too many clamps and had to be forced into place.

There is a circular boss on top of the coolant outlet neck that I drilled and tapped 1/4-27 for my sensor. There casting is not overly thick, but enough to form threads to hold the sensor leak free. I used thread sealing compound. When I did it, the outlet was available for around 40$, so I took the chance.

 

[chap79]

I have one, been on the truck for the past 2 years with no issues. Mines a 38mm inlet/outlet. I did use a new upper hose when I installed it.

 

[kgrove]

I have one, been on the truck for the past 2 years with no issues. Mines a 38mm inlet/outlet. I did use a new upper hose when I installed it.
View attachment 3725302

This looks like what I’m trying to do. Did you start with an OEM upper and cut pieces off? Or you used sections of other hoses to create the correct bends?

 

[chap79]

I just used an OEM hose and just a section out.

 

[kgrove]

I just used an OEM hose and just a section out.

I'm having to go another direction. When I start with the OEM shaped upper hose, the temperature probe housing ends up joining with the return hose in a sharp bend section, so the hose clamp starts applying a good deal of pressure against the hose with the sharp edge of the clamp. It doesn't cut the hose now, but it makes me uncomfortable about it's longevity ... seems like a few years of vibration and heat would inevitably have the hose cut the hose and cause a leak.

What I'm going to attempt is to fabricate my own temp probe housing that is curved instead of straight. If I either buy an already bent section of aluminum pipe or take a straight section and put a slight bend, then weld a bung into the curved pipe. I can then cut maybe 1" out of the OEM hose and clamp the cut sections on my curved probe housing so the result has more reliable clamp joints and the hose closely duplicates the shape of the OEM hose. Hopefully this would last longer. I haven't seen it done, but already found a radiator guy that is going to fab one up for me and he thinks it will work too. I'll post a followup with results. I likely will have him make an extra one as well in case I get another Prado down the road.

 

[epaul]

Had one in the top hose for three and a half years, 20k miles. I do think the best option though is to drill and tap the coolant outlet piece on the motor.

 

[kgrove]

Had one in the top hose for three and a half years, 20k miles. I do think the best option though is to drill and tap the coolant outlet piece on the motor.

View attachment 3756232

I'm going to be using the coolant outlet location. I went down this path, but I was uncomfortable with that area where the clamp for the temperature probe housing attaches on the curved section of the hose between the probe housing and the coolant outlet on the engine. Yours is the second I've seen here that have worked for multiple years, so clearly it's at least a decent solution, but it does seem like a near certain point of failure given enough time. Sooner or later that clamp would have to bite into the hose and cause a split, so it makes me uncomfortable. I guess it's my OCD speaking.

My plan is to weld an aluminum NPT bung on the coolant outlet piece. I thought about just drilling a hole and tapping the outlet fitting in part because I can do that in my garage with tools I already have, but instead I'm going to find a local machine shop and have them weld in a bung so it's a more robust connection with more than just a couple threads (I don't do welding). I'll post a photo of the result when it's completed and installed.

 

[kgrove]

Just picked the part up from the machine shop. This solution makes me much more confident. I was going to have them weld the bung where you see the X on top, but the machine shop suggested the circular ring instead. They drilled a hole in the center of that thing then welded the bung inside.

I'm not equipped or trained for welding myself, so this cost me $75 for a local welding shop to drill a hole and weld in the bung, plus about $10 for a pair of aluminum bungs (only needed one). Here are the photos... the coolant outlet without the temperature probe, with the probe installed, an internal shot to show how far the probe extends into the coolant stream, and the finished product.

The first version, they drilled a hole just barely bigger than the tip of the temperature probe. I think it would have worked, but I was concerned that if the edge of the coolant outlet was touching the temperature probe at all, then the probe wouldn't react as quickly to changes in the coolant temperature as it would be picking up the thermal inertia of the coolant outlet fitting itself. I had them drill out the hole to be noticeably wider than the temperature probe tip just to be sure.

I'm happy with it... It seems more durable than piecing together an upper hose and keeps all my radiator hoses as OEM part numbers.

Incidentally... before I turned this over to the machine shop, I verified the coolant outlet fitting was available as a new part... roughly $100 with shipping, so my worst case scenario was to delay an extra 10 days and spend $100 and replace the fitting the machine shop screwed up. It always feels better to know you can at least get back to where you started.