Problems with highway driving, you guys have these issues?

[jizmac]

So have had my 510 for quite a while and have ran a few different setups on the same L20b bottom end and have always some intermittent issues with highway cruising, actually now I don't even take it out of town because of fear that shes going to leave me stranded.

So as you cruising at highway speeds, my idle will slowly increase, after 20mins or so you could stop and have an idle of 1500rpm or so, up from its usual 900-1000. after 40mins you could be as high as 2500rpm. Now you let her cool down and all is back to normal, and this never happens in town, where I am rarely carrying a steady engine or road speed. Also this does not happen everytime, 25% of the time I would say.

Now here is the odd part, whenever this occurs, it is always accompanied with radiator hose collapse, both of them. You can grab both hoses and they are already touching sidewall to sidewall, and don't appear to be overly hot. if you pop the hood while its running, everything looks fine, shut her down, and within a few minutes they tighten right up.

So over the years I have had two different 32/36 DGV's, and I am currently running dual 45DCOE's, a very sporty cam [ powers around 3000-7000], and have changed out water pumps on a few occasions, just to see if that was the issue. I will say the bottom end is getting tired from lots of abuse, but cant really see what might cause this issues there, as I have had this problem for a decade or so. Radiator flows very well, and engine never shows overheating signs when all this is going down.

Is there something stupid that I might be over looking here? Thanks

[okayfine]

What kind of radiator cap do you have? And is it in good condition? If your cooling system pressurizes during operation and, if necessary, blows coolant out the overflow - but then can't pull it back in as the system cools/pressure subsides?

It's a guess, but that's what I'd look at first. I find it peculiar the rev raise corresponds with the hose collapse.

[dislexicdime]

what radiator do you have? and are you using the stock gauge to read
your temps?

[jizmac]

You know what I cannot remember the last time I changed the cap, good call. I also have added a overflow bottle rather than the blow to ground. I do notice the level does change in the bottle so the cap works, but maybe not all the time and I'll check for overflow blockage.

The rad is a custom built high density fin by Stay Cool radiators, its build with the original style tops and bottoms but core was replaced, I had overheat issues when I first got the car, this really knocked it down in temp. And yes I am still using the original gauge. It seems to work well, but guess that should be changed now that you mention it.


And yeah like I said the symptoms seem to go hand in hand.

[okayfine]

The gauge doesn't necessarily need to be changed, but calibrating it so it gives you a meaningful number for the temp would be a good idea.

[duke]

Are you running a throttle cable to the DCOE's? I had a similar problem a few years back, and figured out the it was the throttle cable sticking. My guess was that it was due to heat soak from running at sustained high rpm's on the freeway. I installed another return spring and have never had it happen again.

[jizmac]

So I should just check it against a calibrated gauge? I guess I could just run a test gauge to be sure.

And Duke I did check the throttle to be sure it was firm against its stopper, but I'll double check to make sure I have enough tension anyways. I did switch to a cable though.

[proflex]

If the hoses are collapsing during -cool down- it’s not getting coolant or air back into the cooling system as it cools. A vacuum valve in the rad cap allows it to return back into the system. Things you can check=
-new rad cap!
-check rad cap sealing area on the rad.
-check return hose and overflow tank for blockages. {Test in the direction of the returning coolant flow, towards rad, cap off}
-check the return hose to see that it’s not too soft {collapsing} and that there are no kinks in the hose.
- drain and check for crap inside the overflow tank that can intermittently block the return hole or hose. Also if it has the hose running into the tank from the top, or filler cap, make sure the hose end that goes inside is not too long / touching the bottom of tank. I cut this hose end at a 45 degree angle just to be safe.
-check the top and bottom rad hoses to see if they are overly soft. Age and oil contamination can make them too soft and cause collapsing.
-when engine is cold check the coolant level inside the overflow tank as well as inside the rad. If the overflow has coolant and the rad is low you may have other problems.

High idle- Try checking your base timing when it’s doing the high idle thing. If the mechanical advance is sticking when hot it will increase your idle speed.

[jizmac]

I will do the full check-over on the cooling system, but I think you might be onto something with the timing, I have never checked it while its doing this.
Thanks for the thoughts guys, I appreciate the help!

[banzai510(hainz)]

if your not running a bypass water line from the lower thermosstat housing I just drill a 1/8 hole in the thermostat. Just helps with the airbubbles better.That I notice.

In the old days Gates used to sell the lower hoses with a coil spring in there to prevent collapse.

i bet your gauge is fine

what is bad if the hose collaspes when you rev up the motor and the water pump really starts sucking.

[jizmac]

Yeah I did remove the bypass, but I plumbed in a removable brass cap so I can manually bleed the air right from there. Works well!