View Full Version : Radiator Cap Issue? SOLVED!
My Blueprint 306 came with a radiator cap rating of 20. Back when I did my first start, I burped the air out of the cooling system.
Now when I drive around and the engine heats up, radiator fluid starts spurting out from around the cap. When the engine cools, I noticed the top and bottom radiator hoses collapse from vacuum. I've read that the likely culprit for this is a bad radiator cap, so I replaced it with new one - also rated at 20. But the same thing occurs.
There is some fluid in the overflow tank and I've confirmed that the overflow line from the filler neck is attached to correct fitting at the bottom of the tank - not the one that extends up into the tank. Both lines are clear from obstruction checked by blowing air through them.
I'm thinking of trying another new radiator cap rated at 16, but is there something else it could be? More air in the system?
Thanks.
Confirm that your radiator cap has a check valve (most but not all do) and that your recovery tank is vented to atmosphere. The problem you describe has nothing to do with the pressure rating on the cap.
AC Bill
10-14-2020, 02:07 PM
You mention nothing about it overheating, or above normal operating temps. Most use a 15-16 psi vented cap. It sounds more like an issue with the overflow bottle set up. Perhaps it's vent is plugged, or it isn't a vented bottle.
That, or your not using a vented rad cap. https://www.coolcatcorp.com/Radiator%20Caps/Radiatorcaps.html
The coolant spurting from the cap, should instead be going down the OF hose to the bottle. If the vent in the bottle is plugged, this would cause pressure to build up. The coolant has to go somewhere, so it comes out the cap.
Likewise when it is cooling down. The suction created, should draw the coolant back out of the bottle, and back to the rad. If the OF hose collapses under vacuum, or the bottle isn't vented, this would cause the rad hoses to collapse.
Now if the intention of Blueprint was for you to use a T filler in the upper rad hose, they may have supplied you with a higher pressure, or non-vented cap to use on the rad, whereas you would use 15 psi cap on the T filler, which is also where your OF hose would be attached. I have that set up, and it works fine. The OF hose spigot on the rad is plugged, and the higher pressure cap is on the rad, so all the pressure release is dealt with at the T-filler.
Thanks for the input everyone.
I'm going to investigate further both Naz and AC Bills responses, but I swapped my 20 out for the 16 and then went for a 10 mile drive - that seemed to do the trick - no spurting from the cap and temp was in the normal range. I'll check to see if the hoses collapse due to vacuum when things cool off.
You mention nothing about it overheating, or above normal operating temps. Most use a 15-16 psi vented cap. It sounds more like an issue with the overflow bottle set up. Perhaps it's vent is plugged, or it isn't a vented bottle.
That, or your not using a vented rad cap. https://www.coolcatcorp.com/Radiator%20Caps/Radiatorcaps.html
The coolant spurting from the cap, should instead be going down the OF hose to the bottle. If the vent in the bottle is plugged, this would cause pressure to build up. The coolant has to go somewhere, so it comes out the cap.
Likewise when it is cooling down. The suction created, should draw the coolant back out of the bottle, and back to the rad. If the OF hose collapses under vacuum, or the bottle isn't vented, this would cause the rad hoses to collapse.
Now if the intention of Blueprint was for you to use a T filler in the upper rad hose, they may have supplied you with a higher pressure, or non-vented cap to use on the rad, whereas you would use 15 psi cap on the T filler, which is also where your OF hose would be attached. I have that set up, and it works fine. The OF hose spigot on the rad is plugged, and the higher pressure cap is on the rad, so all the pressure release is dealt with at the T-filler.
This is really interesting stuff for a novice like me. Thank you and I'm going to take a closer look at everything.
rich grsc
10-14-2020, 05:44 PM
You mention nothing about it overheating, or above normal operating temps. Most use a 15-16 psi vented cap. It sounds more like an issue with the overflow bottle set up. Perhaps it's vent is plugged, or it isn't a vented bottle.
That, or your not using a vented rad cap. https://www.coolcatcorp.com/Radiator%20Caps/Radiatorcaps.html
The coolant spurting from the cap, should instead be going down the OF hose to the bottle. If the vent in the bottle is plugged, this would cause pressure to build up. The coolant has to go somewhere, so it comes out the cap.
Likewise when it is cooling down. The suction created, should draw the coolant back out of the bottle, and back to the rad. If the OF hose collapses under vacuum, or the bottle isn't vented, this would cause the rad hoses to collapse.
Now if the intention of Blueprint was for you to use a T filler in the upper rad hose, they may have supplied you with a higher pressure, or non-vented cap to use on the rad, whereas you would use 15 psi cap on the T filler, which is also where your OF hose would be attached. I have that set up, and it works fine. The OF hose spigot on the rad is plugged, and the higher pressure cap is on the rad, so all the pressure release is dealt with at the T-filler.
The new radiators don't have caps on them.
So, while the Motorad 16 radiator cap seemed to solve the spurting from the cap when the engine came up to temperature, after the engine cooled, vacuum collapsed the lower radiator hose and it was tough to remove the radiator cap because of the vacuum. So it must be an issue with the overflow tank not venting? More troubleshooting to follow.
egchewy79
10-14-2020, 10:14 PM
this is really curious...the overflow tank (if you're using FF provided part) has a metal straw that goes from the bottom of the canister to the middle portion. this straw should be unblocked at both ends, right? If this is the case, it makes me think that the valve connecting your T piece to the overflow tank is not working correctly, which would explain the fluid spurting out of your previous cap and the vacuum condition you're experiencing when it cools down.
I used a larger overflow tank rather than FF5's. Here's my set up. Maybe someone will spot something.
Radiator cap - Motorad 16
136347 136346 136348
Overflow tank is similar to FF5's - overflow from T goes to the bottom of the overflow tank. Excess radiator coolant in the overflow tank would come out the vent. There is fluid in the overflow tank, so the overflow appears to be doing it's job. But the collapsing radiator hoses when the engine cools leads me to believe the vent tube must be blocked.
136349 136350 136351 136352
Ron J
10-14-2020, 10:51 PM
Hi, I had a similar experience. I discovered I didn't have the rad cap tight enough. I thought I did, but I didn't. I know it sounds too simple. When you think the cap is tight, try turning it another quarter turn.
AC Bill
10-15-2020, 03:31 AM
You should have an OF hose designed for the job, as they need to remain open, even when hot. Some rubber hoses can't stay resilient when hot, and get soft, leading to collapse.
The fact that the rad hose is collapsing, indicates that expanded coolant is actually making it into the OF bottle. So as the rad cools, it should suck it back out of the OF bottle. I don't know how much the OF bottle your using actually holds, but you think it would be quite full, when you first shut the hot engine down. Have you ever tried removing the cap at that point? If the bottle is vented there should be no pressure in it even when hot. If there is internal pressure, maybe you have a expansion tank, and not an overflow bottle.
136357136358136359
It's a simple system and from your first description of the issue and your photos, it appears yours is configured correctly. You stated you checked to ensure your recovery tank vent is open (don't assume it is by simply eyeballing it) and the photo of your new cap shows it has a vacuum valve. But the coolant spurting from around the cap (original) should not happen as there is a seal there. Is this still happening with the new cap?
Also, once the system has cooled from normal operating temperature (like over night) does the coolant level in the closed system return to the normal level? I'm assuming you top off the system when filling it??? Note the coolant level in the recovery tank when cold (again, from overnight), is it returning to approximately the same level after each cooling period? These are indications that the recovery system is working properly regardless of the state of the lower radiator hose.
You should have an OF hose designed for the job, as they need to remain open, even when hot. Some rubber hoses can't stay resilient when hot, and get soft, leading to collapse.
Good point. I'll double check that the OF hose is really designed for the job, and not just hose I had laying around.
The fact that the rad hose is collapsing, indicates that expanded coolant is actually making it into the OF bottle. So as the rad cools, it should suck it back out of the OF bottle. I don't know how much the OF bottle your using actually holds, but you think it would be quite full, when you first shut the hot engine down. Have you ever tried removing the cap at that point? If the bottle is vented there should be no pressure in it even when hot. If there is internal pressure, maybe you have a expansion tank, and not an overflow bottle.
Good idea. I'll check the overflow bottle when the engine is hot.
It's a simple system and from your first description of the issue and your photos, it appears yours is configured correctly. You stated you checked to ensure your recovery tank vent is open (don't assume it is by simply eyeballing it) and the photo of your new cap shows it has a vacuum valve. But the coolant spurting from around the cap (original) should not happen as there is a seal there. Is this still happening with the new cap?
No spurting after I swapped the Motorand 16 for the Motorand 20.
Also, once the system has cooled from normal operating temperature (like over night) does the coolant level in the closed system return to the normal level? I'm assuming you top off the system when filling it??? Note the coolant level in the recovery tank when cold (again, from overnight), is it returning to approximately the same level after each cooling period? These are indications that the recovery system is working properly regardless of the state of the lower radiator hose.
Yes, coolant appears to be returning to the same level.
So I think my way forward on this includes:
1. Check the hose from the cap to the overflow bottle and vent to ensure it's designed for the job and not collapsing when hot causing a vacuum.
2. Check the overflow bottle coolant level when the engine is hot and then cool.
If the above items check out, then maybe the collapsing of the lower radiator hose is normal for my system.
Thank you. It may be a day or two before I can check it out but I'll post the outcome.
RBachman
10-15-2020, 06:52 AM
Three other things I did not see mentioned above that may be causing an issue came to mind. One, is the cooling system properly filled? Two, make sure the line from the coolant reservoir is sucking from the bottom of the tank. Three, it sounds like there is excess air in the system or getting onto the system. Water/antifreeze does not expand and contract enough to collapse a hose. For it to collapse like you mention, it's likely due to excess air in, or getting in, the system. When it cools, it can induce a vacuum strong enough to collapse a hose.
FLPBFoot
10-15-2020, 07:39 AM
There is a small petcock on the radiator top on the drivers side. With the system cool I open that and bleed out any air in the system and make sure I get antifreeze out that petcock. Sometimes I have to do several heat cycles and open and bleed it several times to get it all the air out. I add fluid in the cap after each bleed. It seems that the top of the radiator can trap air.
There is a small petcock on the radiator top on the drivers side. With the system cool I open that and bleed out any air in the system and make sure I get antifreeze out that petcock. Sometimes I have to do several heat cycles and open and bleed it several times to get it all the air out. I add fluid in the cap after each bleed. It seems that the top of the radiator can trap air.
Thanks. I'll add this to my troubleshooting list.
More clues: I inspected the overflow and vent hoses for the overflow bottle and they were unobstructed and felt firm - don't think they would collapse with heat. I checked the overflow bottle and there was just a small amount of coolant in it - about the same as in the picture in one of the above posts. I topped off the coolant at the filler neck, secured the cap, and took it out for a spin.
The temperature ran normal and the fan kicked on as programmed. After a while I started to smell coolant - the temp according to my Sniper handheld was 192F; the dash water temp gauge was at 65C (The temp went down below 180F again as the fan continued to run). I pulled over, opened the hood and there was coolant spurting from the radiator cap. I checked the overflow bottle and the level was the same as it was before I took the car out. So, it looks like the overflow function is not operating as it should.
Can it be anything other than a plugged overflow hose or vent? Could the vent not be large enough? Also, back at the garage, I opened the lower petcock and only coolant came out - no air.
Ha! Problem solved. While checking the overflow lines for the third time, I decided to check the filler neck for obstructions and this is what I found. Leftover from the Boig Motorsports cooling tube fabrication? Blueprint Engines testing? Who knows?
136400
It turned out to be some kind of sphere. That's a 1/4 in drill bit for reference.
136401
Crazy! Well, at least I learned a lot about cooling systems. Special thanks to NAZ and AC Bill. Thanks also to everyone else who chimed in with their troubleshooting ideas. Much obliged.
AC Bill
10-20-2020, 01:13 PM
Ha! Problem solved.
That is the craziest damn thing. Is it made of rubber, or? I can't picture where anything looking like that would be used in an engine build, but it would never have passed through the radiator, and I question if it could even squeeze through an open T-stat?
Sabotage perhaps..how you getting along with the little lady?:p
Glad you figured it out finally..
That is the craziest damn thing. Is it made of rubber, or? I can't picture where anything looking like that would be used in an engine build, but it would never have passed through the radiator, and I question if it could even squeeze through an open T-stat?
Sabotage perhaps..how you getting along with the little lady?:p [
Glad you figured it out finally..
Thank you. It was hard plastic I think. I can only guess what it was for. Maybe used to block the overflow spout during leak testing of the Boig coolant tube when it was manufactured?
In any case, the coolant system operates normally now. I've put 30 miles on the car since then and all is well.
TMartinLVNV
10-20-2020, 06:08 PM
Is that something used when mandrel bending the tubes to keep them from getting crimped?
cob427sc
10-21-2020, 07:03 PM
Well, it sure made a perfect backflow preventer valve! One of the roadsters I built a few years ago, I used the plastic radiator cap and "t" that was to go to the overflow tank. Just by luck as hooking everything up I noticed the plastic opening fro the overflow line was plugged with plastic. I would have had the same experience as you trying to figure out what went wrong. Glad you solved it and sorry I didn't read this sooner.
Mark Reynolds
10-22-2020, 10:22 AM
I think that is a ceramic bead that got stuck in the port during the tumble polishing of the silver ceramic coating process.
I think that is a ceramic bead that got stuck in the port during the tumble polishing of the silver ceramic coating process.
I hope that was the only one!
first time builder
10-22-2020, 06:55 PM
I think Mark has the answer !