How to properly size constant tension clamps

jrfuda

Member
Original poster
Supporting Member
Joined
Oct 2, 2024
Messages
82
Location
Fayetteville, NC
TLDR: After replacing my cooling system as outlined here the hose connecting the thermostat housing to the radiator blew off at the thermostat housing today. I must have used the wrong size constant tension clamp. How do you properly size these?

The rest of the story.

I drove my TJ today as my F150 daily was supposed to stay home so the family could load it up for the drive to the in-laws' tonight for Thanksgiving.

About 10 minutes into the drive, I noticed white smoke (steam actually) blowing out of what appeared to be the back right but was really from under the hood. I was lucky to notice it when I did as I only had a few seconds to take the last exit before hitting the Fort Liberty access control point which would have had me a good 10 minutes away from being able to safely pull over and do anything. I exited and went to a nearby 7-11.

I popped the hood and saw the hose was disconnected. I'm pretty sure I oversized the clamp. I was able to recompress it enough with my bare hands to get the hose back on the outlet from the thermostat housing. I topped off the radiator with some 7-11 branded prediluted coolant that was labeled as "being able to mix with any coolant" and drove home, monitoring temps on the Torque app just to be safe. Parked the TJ, cleaned up a bit, switched back to the F150, and drove to work.

I thought I had followed the guide on which clamps to use posted elsewhere in the forum, but I likely used the wrong clamp here. I bought at least two of each clamp, so maybe I used a clamp from one of the areas that needed a larger clamp. I do not think I could compress any of the other clamps with my bare hands enough to remove the hose. I yanked on the ones I could easily access without dirtying-up my work clothes and they all seemed tight.

That said. If I want to be sure I am using the correct size constant pressure clamp, how do I do that? Using the thermostat housing as an example, should the clamp be snug on the housing without the hose attached, ensuring it will be tight when the added diameter of the hose is added?

Another observation. I used this housing (Dorman 902-306). I assume the hose should be pushed up against the stop and the clamp should be centered between the stop and the lip on the output. The current clamp sits a little askew when on the hose - there is not enough space between the hose and the engine for the clamp to be fully centered between the stop and the lip all the way around. Is this likely another sign that the clamp is too big? I have a box full of worm gear clamps if I have too.....
 
If in doubt about the quality or size of the constant tension clamp, just use a worm gear clamp. Never had a problem with using a worm gear clamp.
 
  • Like
Reactions: Link
If in doubt about the quality or size of the constant tension clamp, just use a worm gear clamp. Never had a problem with using a worm gear clamp.

Worm gear clamps are the worst. They won't take into account the expansion of the hose when warm.
 
  • Like
Reactions: James9100
TLDR: After replacing my cooling system as outlined here the hose connecting the thermostat housing to the radiator blew off at the thermostat housing today. I must have used the wrong size constant tension clamp. How do you properly size these?

The rest of the story.

I drove my TJ today as my F150 daily was supposed to stay home so the family could load it up for the drive to the in-laws' tonight for Thanksgiving.

About 10 minutes into the drive, I noticed white smoke (steam actually) blowing out of what appeared to be the back right but was really from under the hood. I was lucky to notice it when I did as I only had a few seconds to take the last exit before hitting the Fort Liberty access control point which would have had me a good 10 minutes away from being able to safely pull over and do anything. I exited and went to a nearby 7-11.

I popped the hood and saw the hose was disconnected. I'm pretty sure I oversized the clamp. I was able to recompress it enough with my bare hands to get the hose back on the outlet from the thermostat housing. I topped off the radiator with some 7-11 branded prediluted coolant that was labeled as "being able to mix with any coolant" and drove home, monitoring temps on the Torque app just to be safe. Parked the TJ, cleaned up a bit, switched back to the F150, and drove to work.

I thought I had followed the guide on which clamps to use posted elsewhere in the forum, but I likely used the wrong clamp here. I bought at least two of each clamp, so maybe I used a clamp from one of the areas that needed a larger clamp. I do not think I could compress any of the other clamps with my bare hands enough to remove the hose. I yanked on the ones I could easily access without dirtying-up my work clothes and they all seemed tight.

That said. If I want to be sure I am using the correct size constant pressure clamp, how do I do that? Using the thermostat housing as an example, should the clamp be snug on the housing without the hose attached, ensuring it will be tight when the added diameter of the hose is added?

Another observation. I used this housing (Dorman 902-306). I assume the hose should be pushed up against the stop and the clamp should be centered between the stop and the lip on the output. The current clamp sits a little askew when on the hose - there is not enough space between the hose and the engine for the clamp to be fully centered between the stop and the lip all the way around. Is this likely another sign that the clamp is too big? I have a box full of worm gear clamps if I have too.....

This resource should help.

Thread 'Part numbers and resources for constant tension hose clamps'
https://wranglertjforum.com/threads...urces-for-constant-tension-hose-clamps.28271/
 
I definitely used the wrong sized clamp on the thermostat housing outlet to the radiator. As I said earlier, I ordered the recommended sizes as listed in the thread on constant tension clamps. It appears I used a second 55, meant for the lower hose from the radiator where it connects to the water pump. I was supposed to use a 47. I replaced it with a 47, which - incidentally - fist almost snug around the bare thermostat housing outlet and now have a tight connection. I compared how much each clamp on all the other connections were compressed compared to the uncompressed clamps still in their bags to ensure myself that the remainder of my connections had the correct size clamp. I drained and flushed everything again to get rid of the 7-11 coolant, refilled with zerex g05 and everything seems fine. I drove it to work today and there were zero issues.
 
Last edited:
  • Like
Reactions: Link
Correct me if I'm wrong, but I don't think the spring clamps can be too tight. If you don't have a reference number just the smallest you can get on.