Radiator Issue

Ron Bartell

Ron Bartell

Well-known member
Caution - Long Post

At Sebring this weekend my first run with a new radiator had no issues with temps and everything was normal with water around 185 to 190. My second run had normal temps for most of the run but towards the end it got hot and boiled over. I couldn't find anything wrong other than being down on water level a little bit, and since the first run was fine I just topped it off for the first race. I overheated on the parade lap and went into the pits, race over.

At this point I was thinking head gasket, but all the vital signs were ok. After it cooled off I started it up and didn't like what I felt for heat dispersion in the radiator. It was hot going in and cold coming out. We thought that it might have been made wrong with a baffle in the wrong place or something. Since the only thing different on the car was the radiator, I put the old one back in for the second race. It seemed to run hotter than normal but didn't overheat.

After thinking it over I remember being hit with water coming out from under the hood as well as steam when it was overheating. The catch tank didn't have that much water in it so it wasn't overflowing. I am now thinking it must be the cap either being bad or somehow not sealing. The little red lever was kind of funky and could look like it was down and not be all the way.

Has anyone got any experience with overheating from a bad cap? If you don't have pressure in the system will it overheat even though it runs cool enough normally? I always thought that having a pressurized system just raised the boiling point, but will you boil over without it?
 
Ron:

Not a direct answer to your question but maybe it will help.

A couple of years ago I put a pressure sensor into the cooling system. It is adjustable and I set it so a warning light will go out when it reaches about 8 psi. I use a 13 psi cap. If I ever lose a hose or the cap doesn't seal I will know immediately as the BIG yellow light (right next to the BIG red oil pressure light) will come on.

John Hewell

#29 GTL/HP Spridget
 
I had a similar problem when the hood would gently poke at the radiator cap at speed. This poke was enough to relieve the pressure from the system.

I've also had more than my fir share of hose clamps loosen up. And yes, I safety wire them and use ABA clamps. They just barely weep at race pressures (22+ psi).

Just a thought.

-Kyle
 
Ron,

Trying to think this through in my head. Early Spridget radiators had deep throat and used special radiator cap only available @ 17 PSI. Later Spridget radiators had standard throat and used same caps as modern cars. Early caps would not tighten in later radiators, but later caps would tighten in early radiators, just not seal/build pressure.

Suspect your radiator is aftermarket aluminum, but is it possible?

RJS
 
Something else to consider IF your cap isn't sealing...
At the higher RPM a race engine runs, it's quite possible that the coolant can be cavitating around the water pump with no pressure in the system. it's an issue on some of the smaller Nissan engines at higher RPM. above 6000rpm with factory pulleys, the pump just turns antifreeze into green foam. since street cars spend so little that high, it's not a problem to occasionally turn 7000rpm on that engine.
As soon as you get to a race track and you're above 5000rpm all the time, cars start to overheat due to cavitation. There's 2 fixes there:
1. higher system pressure. That's a concern with plastic radiator tanks and factory heater core + hoses.
2. underdrive pulley(s) for crank and water pump. slow down the RPM so the impellers don't whip the coolant into a froth. slower fluid flow is better than whipping it into foam and then having zero fluid flow.

If your cap isn't sealing well, I'd consider the cavitation a reasonable scapegoat, even though the system would function normally at 180-190deg when the cap was sealed. even at 180 deg, you're going to be at 7psi of system pressure just from the vapor pressure of water. This pressure helps prevent the pump cavitation..

something else I just ran across makes a ton of sense too... If your radiator cap is on the inlet side of the radiator, your radiator cap is less effective due to the pressure drop across the radiator. i.e. at full fluid flow, there's a (random number) 10PSI drop of water pressure between inlet and outlet of the radiator. So a 22lb cap at the radiator inlet is only as effective as a 12lb cap at the radiator outlet. While not necessarily the answer you're looking for, it's good food for thought when you're considering the cooling system as a whole. It also makes some sense that if your new radiator has more restriction (and thus pressure drop) than the old one, your current cap may be blowing open at lower temps just from the restriction in the radiator.

http://stewartcomponents.com/index.php? ... tion_id=14 Caveat: it's posted on the internet, so it MUST be true. all of this makes for good theory and sounds correct from a theoretical perspective, but I don't know just how exactly true all of it is. It's again simply food for thought.
 
Ron,

Just call C&R racing in Indianapolis and ask to speak to an application engineer. They do all of the NASCAR Cup custom radiators as well as Indy Car. Maybe some F1 behind closed doors. I've been to their shop numerous times and everything is well conceived and built to the highest standards with no excuses. The owner Chris Paulson is recognized as one of the most knowledgeable race car cooling experts in the industry.

C&R designed and built my 2nd SM radiator (the Super HD aftermarket Japanese unit just couldn't handle drafting in hot weather). It was a work of art that performed even better.

http://www.crracing.com/
 
Referencing the John Hewell post.

My car has a Honeywell pressure sensor single pole double throw for water and for oil. A green light for good pressure and a red light for below an adjustable limit pressure.
 
Thanks for the responses. Didn't get an answer on whether a system that normally runs cool will definitely boil over if not under pressure, other than the info about cavitation. I assume cavitation results in the circulation being less than adequate, so the fluid stays in the head and block too long and can boil over because of that?

Some more info on the problem and my system. The radiators are identical, old and new, at least as far as I know. They are from Griffin and are nice pieces. The radiator cap is not on the radiator but on the separate fill tank. There is nothing in the system that is Spridget except for the water pump. The set-up has worked for two years with the old radiator and cap. The cap is 16 lbs I think (not near me at this time).

The pressure sensor is a good idea and would help troubleshoot this problem for sure.
 
Hey Ron - not sure if this will help... I ran the same exact cooling setup as Joel did for many years and had issues from day 1 as long as it was over 70 degrees ambient. This is what led to the overheating, which led to being rope towed at BeaveRun in 2012, which led to... well, you know the end of that story. Joel never had overheating issues, and I'm pretty confident that he ran in hotter ambient temps in the southeast than I was in the northeast. So, it came down to two things being the culprit for the hydrolocking that was occurring... unpressurized system (old/broken cap), or hung thermostat. Unfortunately, I was so pissed with what happened at the aforementioned race that I re-plumbed the entire cooling system with Craig Chima's assistance, put in a thermostat blanking sleeve, and got a new cap, so I never pinpointed the root cause for the overheating. Haven't had an issue since the rebuild.
 
Ron, I would pull the head and check the gasket. No offense to the others who offered advice but I would pull the head. I don't know when the last time it was off, but it couldn't hurt to do an inspection and maybe freshen the valve job before the nationals. Sometimes we over think these things. Good luck.


Kerry Foote
 
Ron in answer to you question i believe it will, due to hot spots in the engine causing local boiling, near 180d with low pressure. This leads to steam pockets. Something similar can happen to hot water heating systems which use steam to water heat exchangers or if they get air in them. i also think the discussion above about cavitation is related. Pump won't move air or steam. I had similar problems until i went to a cross flow and raised the pressure.
 
I have all kinds of problems with caps and cap seal over the years. While I did it for head gasket issue diagnosis, I have a turbo boost gauge on the dash that is plumbed into the cooling system and reads cooling system pressure. Super easy and cheap.

Also, what is the deal with that little hose that runs up from the water pump to the head on the 1275? When I built a 1275 for my Turner a few years back I was told to leave it off and block it off. However, I had difficulty getting the cooling system to bleed until I reinstalled it. Never bothered to think it through further after it worked.
 
Ron... Didn't get a close look at your cooling system last weekend but I've got a Griffin double cross flow, 180 thermostat, high rear mounted flow-through tank from the rear of the head with a 13 lb cap and an expansion tank. I ran 182 degrees in late morning Sunday's race and usually run 185 if the temps are in the 90s. Also have a 2 to 1 pulley ratio on my pump drive. Both radiator hoses are on the left side so I jack up the left side of the car to make sure there aren't any air pockets while filling the system. That said, I wouldn't discount Kerry's head gasket comment. My system must be pretty efficient because the forced air box intake is mounted in the grill and takes at least 1/3rd of the intake air.

Bob
 
Ron, Kerry is right that is makes sense to check the head gasket since it is way easier on your car than some of the OHC cars. To your question, yes, failure to seal at the cap can cause boil over which then causes overheat. The temp of coolant right next to the combustion chamber is way higher than the overall temp at the outlet-where most temp sensors are mounted. The high pressure on race-type caps lets us get prevent localized boil over. Once you get air in the system from boiling, chance of overheat gets much higher.
 
Tom Broring":3m6ok5w1 said:
Ron, Kerry is right that is makes sense to check the head gasket since it is way easier on your car than some of the OHC cars. .
Click to expand...
Kerry is forgetting that I ran a race after the boil over problem so it wasn't the head gasket. As I said in the original post I also thought it was a gasket, but checked vital signs (compression and leakdown) and they were fine so I knew it wasn't that.
 
Ron, good information from every one.

To answer your question, yes. With a loss of pressure, from a defective cap, you will loose coolant and temps will rise. And all the other issues discussed will surface.

You didn't mention if you have done a pressure test on the cap, using a radiator cap tester. You also didn't indicate how much coolant you had lost/replaced. Are you using a header tank, with the cap being the highest point in the cooling system?
 
Ron - saw you at Sebring while I was flagging and you mentioned this at lunch Saturday. Here is the mechanical engineer/former sprite racer's thought: When a formerly working system fails to perform with a new part, you should suspect the new part is defective, or improperly installed. You stated "a NEW Radiator" performed okay for one session, but then the car overheated partly through the second. The good performance in the first session seems to validate that the installation was okay(air pockets, etc and level of coolant)- and we assume nothing else was changed for this weekend other than a new radiator.
All of the comments about pressure and cavitation are valid concerns but I don't think they are the problem here, or you would have had this problem before.
The two keys are 1) your comment about overheating in one lap - it takes time to build up heat in the engine, but even a marginal system would take longer than one lap to overheat...Thus, some LARGE change happened during the second session. 2) You noticed that the top of the radiator was hot but the bottom was cold. This is a double-pass NEW radiator, right?
So what I propose is that some internal baffle was incorrectly welded/brazed and came loose during the second session. The car was trying to pump engine-heated water but there was only a small path through the mid-point of the radiator- thus the top was hot. There was so little of the hot water making it past the obstruction into the lower half that it mixed with the cool water in the lower half and thus the lower half felt cool. But the overall flow rate was small, so the car overheated rapidly.
The fact that it again ran okay later with a different radiator re-validates the rest of the system. Something has come loose internally in the NEW RADIATOR and is blocking most of the flow. You could test both radiators out of the car, held vertically, with a garden hose clamped into the inlet hose and note how much water flows through the outlet... (be careful not to apply too much pressure, of course and leave the outlet open.) Hope this helps! Joel
 
What Joel said. Plus:

Now connect the hose to the outlet and backflush it. If a red rag or a mouse nest pops out, there's the problem. Also, a sometimes problem that can occur is a water pump inlet hose that sucks itself shut (flat) sometimes. Usually if the motor gets wound out when the thermostat is still closed and there is no pressure to keep it inflated, but could happen later if the system loses pressure, or if the radiator is restricted. That's why some OEM lower hoses come with a steel coil spring inside.
 
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