Renix: Losing coolant, no hose/rad leaks, pressure cap? Hey Joe, little help...

Hey all-
I had the pressure bottle filled up to about 2/3 full. After maybe 1k miles I'm down to less than 1/4 full. I replaced all the hoses and check for leaks just about every time I go to drive.

It usually runs at the line before 210 on my gauge. The other day it was getting to 210 and a little above. It got hotter at stops, cooler when moving. I assume this is the fan clutch (will do soon regardless).

Today I filled the bottle back up and it ran at it's normal temp line again just fine.

My question is: if my pressure cap is not sealing right how much coolant could be lost out of it? I sort of worried that the amount I lost is more than could leak out the cap= bigger issues. There is a tiny puddle visible around the base of the cap, but nothing major below it. Could it be evaporating hot vapor and not puddling?

I remember Mr. Joe_Peters had a link to a better cap-
ETA: found it- Volvo Stant 11244 changed to 10224

I'm not able to check compression right now, but the motor runs as it has for the last 5k or so. Hoping it's not the head gasket (no other symptoms-oily coolant, milky oil- that I've noticed).


Oh yeah, my coolant mixture may be a little rich, but it was working great up until it got low.

Thanks...

This is the cap I'm finding


It looks like the threads are on the outside, whereas Renix are on inside of cap.

A bad radiator cap would lead to expelling more liquid into the overflow tank. Repeatedly doing this will lead to a loss of fluid due evaporation.

You should replace your radiator cap approximately every two years. Also, contrary to what many parts houses list, the cap should be a 16lb cap, not a 14lb cap. A 14lb cap can lead to this issue.

There is another not so good possibility. You could have a head gasket leak. Replace the radiator cap first and see if the issue goes away.

Stant is a normally a good brand. There are premium brands out there, but have never found the need to go that route.

you wont loose any coolant with a bad seal at the cap, it just wont build pressure. the problem you are having is that when you replaced the hoses, you may not have filled the system with the proper amount of coolant or you have an bubble/pocket and the system needs to be burped.

when i fill the system in my 89, i do a few things to get the right amount.

first i drill 2 very small holes in the thermostat. 6 oclock and 12 oclock. this allows for the air in the system to pass through.

second, i fill the system by removing the top radiator hose from the radiator and pour the coolant down the hose.

last, i connect the hose and run the engine until hot. shut engine down. remove cap(carefully) to the expansion tank, add coolant if nessacary.

most likely, all you need to do is add more coolant because there was air in the system and you never had the correct amount in the system to begin with.

First, 2/3 is too much. If you look into the opening, you'll see a small molded knotched post sticking up. Fully cold, the coolant level should fall within the knotch. That makes the bottle about 1/2 full.

If your cap is leaking you're not only loosing coolant, but you reduced the pressure which results in reduced cooling capability. How much depends on the size of the leak. You definitely have a bad cap.

I only burped it at the temp sender, so I guess it could have had a little air in it. It ran fine and operated consistently at the line before 210* though.

I guess now I just need to find the right Volvo Stant cap...

Can anyone verify if the photo in the first post is the right one?
I found the same image at AdvancedAuto and PepBoys- Stant 11244

HenryKrinkle said:

I only burped it at the temp sender, so I guess it could have had a little air in it. It ran fine and operated consistently at the line before 210* though.

I guess now I just need to find the right Volvo Stant cap...

Can anyone verify if the photo in the first post is the right one?
I found the same image at AdvancedAuto and PepBoys- Stant 11244

Click to expand...

that is it.

i will getting one in the future, but for now, i have a hose clamp around the cap right to keep it tight. ive been running it this way for a few years without any issues.

A "blown" cap can and do cause coolant loss. The pressure maintained by the cap causes the coolant to boil at a higher temperature - loss of pressure will depress the boiling point again, and that means you'll have steam escaping the system.

You gain 3*F from the normal 212*F boiling point for each 1psig of the cap - so a 16psig cap means you'll be boiling at 212*F + 48*F = 260*F. Design temperature of the 6-242 is 210-215*F, so you're right on the edge of boiling at atmospheric pressure... (The reverse is also true - you lose 3*F margin for each 1psig you lose over the water. I'll leave looking up the decrease in boiling point due to altitude as an exercise for the pupil.)

Given that this is a plastic tank, it's also fairly common for it to crack along a seam line or a mould parting line after a few years. I'll source replacements from Morros 4x4 Center - for a decent price, you get a new tank (by Crown, which is a brand that has always treated me well so far) and a new cap stuck on it (also Crown.) I've been replacing caps every five years without incident.

Other things that can help:
- Drilling the thermostat. As mentioned above, drill the two holes in the tstat. This will help prevent a "steam void" behind the thing, and will help get the initial air pocket out from behind it as well.
- Water Wetter, by RedLine. I love this stuff!
- Make sure your fan clutch is up to scratch. On the XJ, it is not a "lifetime" part, it is a maintenance part. About every five years, and I find it a good habit to pick a flat spot you'll be able to see easily with the thing installed, and write the date you installed it there (ditto the cap. Ditto the mileage on the oil filter. You can eventually accumulate enough vehicles that you lose track, and I have CRS anyhow.)
- If you have the thermostat out, check the inside of that housing. A grinding burr (not a stone!) will work neatly for getting any casting flash and surface irregularities out of the thing - which can impede coolant flow.
- Blast your radiator fins out with a garden hose, from the engine side! I've seen some amazing crud get stuck in there...
- Degrease your engine. You wouldn't normally think of this, but a clean engine is a cool engine - it doesn't get rid of heat simply through the radiator!

Thanks a bunch for the tips! I'm on my way to advance for the volvo stant cap. Will check the bottle for any cracking. Also will do the Napa 272310 Heavy Duty fan clutch soon.

My cap has stripped out before. Right now I tighten it to JUST the point where I think it'll break free.

Can't wait to have a more solid, worry-free system.

Thanks again fellas....


So a system at 16 psi wouldn't boil until 260*. I just read the closed Renix system operates at lower pressure- something like 8 psi when warm. So it would only be good until 236*. I assume the fans help keep that from happening.

5-90 said:

- Blast your radiator fins out with a garden hose, from the engine side! I've seen some amazing crud get stuck in there...
- Degrease your engine. You wouldn't normally think of this, but a clean engine is a cool engine - it doesn't get rid of heat simply through the radiator!

Click to expand...

I'm not sure I should do either of these on my 91. I am certain that I would (a) flush all the fins out of the radiator and (b) bits of the engine would fall off without the dirt and grease buildup holding them in place :roflmao:

I had to push some of the rows of fins back into the radiator last time I was screwing around in that area. It is well beyond its last legs.

Also note that the boiling point of a 50/50 mix of water and Ethylene Glycol is 225F.

HenryKrinkle said:

Thanks a bunch for the tips! I'm on my way to advance for the volvo stant cap. Will check the bottle for any cracking. Also will do the Napa 272310 Heavy Duty fan clutch soon.

My cap has stripped out before. Right now I tighten it to JUST the point where I think it'll break free.

Can't wait to have a more solid, worry-free system.

Thanks again fellas....


So a system at 16 psi wouldn't boil until 260*. I just read the closed Renix system operates at lower pressure- something like 8 psi when warm. So it would only be good until 236*. I assume the fans help keep that from happening.

Click to expand...

The pressure bottle cap number has changed, it is now Stant 10244, fits mid-eighties Volvo 740 with the 2.3 L engine.

Your cap not sealing properly is most likely the coolant loss point. The Stant 10244 will seal very well on the XJ pressure bottle, it has a lower profile so when the pressure bottle expands it won't impact the hood and promote cracking of the bottle--check the underside of your hood, you will most likely see rub marks from the cap; it has a higher pressure rating so it will raise the boiling point of the coolant.