BJ70 new radiator - twin pressure caps

[bj70import]

The 3B has a pressure cap as the highest point on the engine. The stock radiator has no cap or holes apart from the inlet/outlet & drain plug.

A new radiator from Toyota is out of the question, and ideally I'd like something with a bit better cooling capacity. Various later models of Landcruiser radiators will fit, however they are all designed for an engine without its own pressure cap.

If a radiator with its own recovery cap was to be fitted, 1. is it possible & 2. how should this be gone about?

The cap on the radiator would be more or less an inch and a half lower than the engine cap.

My initial thoughts was to put a t-piece in the recovery hose, one going to the radiator cap and one going to the engine cap. After further consideration though I thought that when under pressure the coolant would overflow, not out of the engine cap, but out of the radiator cap, decreasing water levels until it was inline with the lower cap on the radiator. This would mean only the bottom 1/3rd of the radiator hose would have coolant going through it.

Then when it gets sucked back in it would take the path of least resistance, that being the one to the radiator filling level instead of right up to the engine level.

My other solution would be to block off the coolant recovery hose of the new radiator and just keep the overflow going solely to the water outlet.

Thoughts?

 

[Chris Harbrow]

The 3B has a pressure cap as the highest point on the engine. The stock radiator has no cap or holes apart from the inlet/outlet & drain plug.

A new radiator from Toyota is out of the question, and ideally I'd like something with a bit better cooling capacity. Various later models of Landcruiser radiators will fit, however they are all designed for an engine without its own pressure cap.

If a radiator with its own recovery cap was to be fitted, 1. is it possible & 2. how should this be gone about?

The cap on the radiator would be more or less an inch and a half lower than the engine cap.

My initial thoughts was to put a t-piece in the recovery hose, one going to the radiator cap and one going to the engine cap. After further consideration though I thought that when under pressure the coolant would overflow, not out of the engine cap, but out of the radiator cap, decreasing water levels until it was inline with the lower cap on the radiator. This would mean only the bottom 1/3rd of the radiator hose would have coolant going through it.

Then when it gets sucked back in it would take the path of least resistance, that being the one to the radiator filling level instead of right up to the engine level.

My other solution would be to block off the coolant recovery hose of the new radiator and just keep the overflow going solely to the water outlet.

Thoughts?

Curious as to what you did here in the end. I’ve just replaced my old leaky brass rad on my 3b and now have two caps in the situation you describe above. Looking for ideas

 

[Nz Nath]

I have a 13bt in a landrover. The landrover radiator cap is higher than the cap on the thermostat housing. The rad cap opens at a lower pressure, I was advised to use a low pressurure cap as the rad was designed for lower pressures (think I've got 8psi cap now). When I got the truck the hose coming from the thermostat housing cap was just left to vent into the engine bay. Eventually I found traces of coolant coming from it, and it seemed to be getting worse as the thermostat housing cap was in poor condition. I replaced the cap, and made a second hole in the overflow bottle and routed the thermostat hose into it.

This works fine, I don't believe the thermostat cap ever vents since replacing it. I use the rad cap for checking coolant etc. If you open both caps together obviously coolant overflows out the lower one. As long as the higher cap opens first (lower pressure) any air sucked in should always get vented out again when hot before coolant is pushed out

 

[dare]

I converted my BJ73 to a HDJ79 radiator so I've been running twin caps for about 3 years. I removed the barb for the overflow hose and tapped the thermostat housing for a bung. I had problems with the aluminuim surface the cap sits on being corroded so the system wasn't holding pressure. I fitted a higher pressure cap on the thermostat housing and I run the overflow hose off the cap on the radiator. This works fine and the height difference isn't as much as it looks, on mine if you open both caps at once on a level surface you don't actually lose any coolant.

 

[Sanyano BJ75]

The 3B has a pressure cap as the highest point on the engine. The stock radiator has no cap or holes apart from the inlet/outlet & drain plug.

A new radiator from Toyota is out of the question, and ideally I'd like something with a bit better cooling capacity. Various later models of Landcruiser radiators will fit, however they are all designed for an engine without its own pressure cap.

If a radiator with its own recovery cap was to be fitted, 1. is it possible & 2. how should this be gone about?

The cap on the radiator would be more or less an inch and a half lower than the engine cap.

My initial thoughts was to put a t-piece in the recovery hose, one going to the radiator cap and one going to the engine cap. After further consideration though I thought that when under pressure the coolant would overflow, not out of the engine cap, but out of the radiator cap, decreasing water levels until it was inline with the lower cap on the radiator. This would mean only the bottom 1/3rd of the radiator hose would have coolant going through it.

Then when it gets sucked back in it would take the path of least resistance, that being the one to the radiator filling level instead of right up to the engine level.

My other solution would be to block off the coolant recovery hose of the new radiator and just keep the overflow going solely to the water outlet.

Thoughts?

Hello, I saw your post, and I would like to ask you how you solved the problem of the double radiator cap.

I bought a BJ75, with a 3B engine, which does not have the original dadiator, it has a radiator with a cap.

How did you solve this problem? I feel like the cooling system is not working properly.

I am thinking of installing a 1.1 bar cap on the radiator, and a 0.9 bar cap on the thermostat.

Balances from Chile, South America