First time overheating my '66 BB!!

[Andrew S.]

This probably won't be the last time my BB overheats, but I have a few questions about my experience in my '66 L36 yesterday. Please bear with my lack of automotive knowledge. At least I knew enough not to take off the cap when it was boiling over!

1) Once it started overheating and the coolant started boiling, it pretty much just dumped every last drop of its coolant all over the highway. Is this supposed to happen? I don't have great pics of a completely unmolested L36 radiator (I have a service replacement in mine) to see if that tube under the cap (an over flow tube?) is supposed to be connected to something, and mine's just missing whatever that 'thing' is.

2) Not using lead additives: possible culprit? In the category of "if it ain't broke, don't fix it" I read an old thread on using fuel and lead additives and came away with the impression that there's no need for them. I use pump 93 octane here in Illinois. The incident yesterday happened while I was using my first tank of straight, no lead-additive gas. Could this have contributed to the problem? My brother has a '67 Cougar and notices that it runs much cooler using premium and a lead additive.

I should add that for the 3 weeks I've owned it, it ran just slightly left of 'high noon' on the temp gauge.

And if there's a good source for photos of pristine L36 engines out there, I would appreciate it. I have Noland Adams' Vol. 2 as a photo reference, but that's it.

Thanks for the help!

[John H.]

Re: First time overheating my '66 BB!!

1) Once it started overheating and the coolant started boiling, it pretty much just dumped every last drop of its coolant all over the highway. This is supposed to happen, right? I don't have great pics of a completely unmolested L36 radiator (I have a service replacement in mine) to see if that tube under the cap (an over flow tube?) is supposed to be connected to something, and mine's just missing whatever that 'thing' is.

2) Not using lead additives: possible culprit?

Andrew -

That nipple just below the radiator cap should have a rubber hose on it that goes down next to the frame so coolant dribbles on the ground.

What were the conditions when the overheating occurred? Highway speed, or traffic, or?

Had you topped-off the coolant level recently?

Where did the replacement radiator come from, and does it have the same cooling capacity as the original?

Are the factory fan shroud and fan clutch in place?

Have you verified the ignition timing and advance map and functionality of the vacuum advance?

Your L-36 shouldn't overheat, and fuel/additives have nothing to do with it.

[Andrew S.]

Re: First time overheating my '66 BB!!

1) a rubber hose on it that goes down next to the frame so coolant dribbles on the ground.

2) What were the conditions when the overheating occurred? Highway speed, or traffic, or?

3) Had you topped-off the coolant level recently?

4) Where did the replacement radiator come from, and does it have the same cooling capacity as the original?

5) Are the factory fan shroud and fan clutch in place?

6) Have you verified the ignition timing and advance map and functionality of the vacuum advance?

7) Your L-36 shouldn't overheat, and fuel/additives have nothing to do with it.

1) A nipple-affixed rubber hose, I got. And it was more of a spray than a "dribble" last night.
2) Started getting hot in traffic, then highway didn't make it any better. Total running time was about 5 minutes in traffic, 5 minutes on the highway before it topped out at just below red line temps.
3) No. It took a full gallon last night after the incident, though (And -- stupid me -- I just realized it's been awhile since I checked it). However, after letting it cool for about 4 hours last night and then filling the radiator up and trying to run it again, it still got hot after about 5 minutes of driving around the block. All of the hoses appear solidly clamped and not leaking, but I'll check that, too.
4) Not sure -- will have to verify.
5) Fan shroud = yes. Fan clutch? Briefly, where and what is it? I have Chiltons and the Chassis Service Manual, so I'll look there.
6) No -- but I've seen the recent good posts on that topic, so I will check it out.
7) Good to know. I'll tell my brother he's still wrong.

[Rob M.]

Re: First time overheating my '66 BB!!

Andrew,

I agree with John. 5 minutes of traffic and highway speeds should not be reason to overheat. Like John said, I would ensure that the radiator, fan shroud, and fan clutch are correct and functioning correctly. If they are, it is most likely a timing issue.

If you search the archives you will find many very informative posts on correct timing, correct vacuum advance, etc.

Sounds like you recently purchased the car - congrats! Sorry to hear about your issue. Good luck.

[Steven S.]

Re: First time overheating my '66 BB!!

I would also pull the thermostat out and verify it is opening when it should, if you replace it I suggest checking the new one as well before putting it in.

[Jean C.]

Re: First time overheating my '66 BB!!

Andrew,
Is the fan belt in place?
Best regards,

[Joseph K.]

Re: First time overheating my '66 BB!!

I would also pull the thermostat out and verify it is opening when it should, if you replace it I suggest checking the new one as well before putting it in.

I agree with Steve. To heat up so soon it sounds like the thermostat. If it is not the thermostat it you should look at the other items mentioned in the previous postings.

[Jim T.]

Re: First time overheating my '66 BB!!

Driving on the interstate on a day trip and in my usual scan of the oil and temp guages in my 70 I noticed the temp guage showing hotter temp. Stopped just before it maxed out. Checked the coolant just before the trip and saw no leakage.
I had a new thermostat in the glove box for times like this, and when the engine cooled enough I removed the old thermostat and installed the new one. Was lucky to drive only a couple miles to get more coolant.

[James W.]

Re: First time overheating my '66 BB!!

Driving on the interstate on a day trip and in my usual scan of the oil and temp guages in my 70 I noticed the temp guage showing hotter temp. Stopped just before it maxed out. Checked the coolant just before the trip and saw no leakage.
I had a new thermostat in the glove box for times like this, and when the engine cooled enough I removed the old thermostat and installed the new one. Was lucky to drive only a couple miles to get more coolant.

Andrew

No one has mentioned it yet, so I will. Check your radiator cap. Big blocks are hard to keep cool, even with all the seals and good clutch and radiator. Sometimes people will put on fan spacers to eliminate the fan clutch. Guess it looks cool. 10 minutes of running is pretty quick. It takes a while for all that cast iron to heat up, so it sounds more like a blockage of some type or one of the items mentioned.

Jim

[David C.]

Re: First time overheating my '66 BB!!

You need to have all the shroud to radiator seals installed, plus everything mentioned above. You can find pretty good pictoral reference (online or catalog) of these from some of the better parts suppliers.

I would start the car up cold with radiator cap off, hold at high idle (1500 rpm), look in the fill hole with a flashlight and see if and when coolant starts to circulate, which will happen when the thermostat opens. You will also be able to determine if the radiator is plugged, or has poor flow.

[Jack H.]

Re: First time overheating my '66 BB!!

In addition to what others are saying, you do know that the big brass Harrison radiators employed internal vs. external coolant expansion space... That means you don't fill them all the way to the top because if you do, they'll 'puke' the extra coolant to 'make' the space necessary.

[Nick L.]

Re: First time overheating my '66 BB!!

The fact that the problem seems to be so "sudden" causes me to suspect a thermostat failure as others have stated. I have recently done some restoration work on the cooling system in my 67 427/400 and it absolutely does not run over a confirmed (with two IR guns) 185 degrees F under any circumstances. This is with a correct replacement radiator, NEW GM fan clutch, and NEW Mr. Gasket high flow 180F thermostat. I have also installed the Dewitt's temp sender calibrated correctly to the factory gauge and verified it reads correctly. I have also applied full time manifold vacuum to the distributor.

Where in the Chicago area are you located? I'm in the western suburbs, may be able to offer some help troubleshooting if you need it.

[Stuart F.]

Re: First time overheating my '66 BB!!

To all my old Vette friends in the western suburbs of Chicago (from a former Hinsdale & Aurora resident) - it's time to kiss your cars goodnight for the winter. That means you have about 4 or 5 months to figure out your cooling system problem. Lots of good suggestions here to start with.

Gad zeeks! I'm sure glad to be living here in Florida now so I can continue playing with my baby. Mid to upper 70's low 80's daytime, low 60's at night - just nice top down jacket weather for us.

Stu Fox

[Andrew S.]

Re: First time overheating my '66 BB!!

I went with the suggestion of changing my thermostat, but now my water temp gauge doesn't work! It worked fine before I replaced the thermostat.

I replaced the 180 thermostat with a 160. The thermostat I took out looked fine, but there was a lot of scale behind it when I took it out. Maybe the thermostat became blocked by scale and that caused the overheating. It definitely needs a flush.

Returning from the test drive, there was a steady steam of coolant coming out of the tube, but I can't tell if that was the result of me having just filled it or overheating.

Is there anything I could have mistakenly done while changing the thermostat (I didn't touch anything else...) to cause the temp gauge to stop working?

Thanks again!

Andy

[Joe R.]

Re: First time overheating my '66 BB!!

Andrew,

The temp sending wire is connected to the sending unit right by the thermostat housing. It's a green wire with some black insulation around it.

Reconnect the wire and everything should be OK with the temp. gauge.

My suggestion would be to find a good service department and take your new acquisition to a good mechanic.

JR