C2 L75 - How hot is too hot?

[Mark H.]

I experience the same problem I've seen discussed many times on the board - creeping temp readings at idle. Engine is freshly rebuilt to stock specs. I've got a new replacement DeWitts radiator, proper distributor advance, rebuilt water pump and a fan clutch that appears OK. It's a '64 and I added some insullation between the radiator and shroud but did not see any difference in operation. As long as I'm moving, the gauge stays right at 180, maybe a tick above. This is only slightly off from actual based on an IR thermometer reading. If I sit at idle, though, the needle creeps up to the first hash mark (220?) and sits there over the course of 5 minutes or so. Once I start moving again, she comes right back down to 180, again in about 5 minutes.

Is this as good as it gets? Should it be able to idle for hours w/o an increase in temperature? Most importantly, if it runs at 220 for an extended period, will I do any damage? Thanks.

[Joe C.]

Re: C2 L75 - How hot is too hot?

Mark:

If it only takes 5 min to get to the first mark, then I would say that there is something wrong. Wire your heat riser wide open. Make sure that your vac advance is operating properly. Sometimes an air bubble in the cooling system takes awhile to work its way out. Is your idle mixture too lean? Can you swap in a known good fan clutch as a test?
You should be able to idle the engine for about 45 min, on a 90 degree day, without moving, before it actually boils over. I have never heard of anyone idling the engine indefinately, on a very hot day, without moving, without boilover.

Joe

[Les Jacobs]

Re: C2 L75 - How hot is too hot?

Hi Mark I have an L76 with exactly the same symptoms(?). Ive done everthing I can(except the new rad) to cure it (including wiring the exhaust crossover open, and new fan clutch), and while it has improved it still moves up a hash mark when in stop and go traffic for more than 3 or 4 minutes (or idling on a hot day). I think the temp approaches 205 or so (IR), but Ive never let it go higher than that (usually shut it down, or find a way to get up to speed). I shudder to think what might happen if I get stuck in a real traffic jam. I'll be interested in seeing what other responses you get.

[Mark H.]

Re: C2 L75 - How hot is too hot?

I should add that other than the usual puking when first filled, she has not actually boiled over. I am also not very confident in my use of the IR thermometer - I try to use the upper hose and the water outlet on the top of the engine, but sometimes get varying readings.

Vacuum advance works fine. Heat riser is wired open. What's the best way to check for or purge an air pocket?

[Richard D.]

Re: C2 L75 - How hot is too hot?

Mark, I've been working on an overheat problem on my 68 L79, and got a lot of good advise a few weeks back.

While gathering info. on what to do to address this, I read that if the upper rad. hose is higher than the aluminum fill tank, it will probably have air in it.

So, while filling the system, I manually compressed the hose a couple times, and got coolant to suck back into it.

It did help a bit on the overheat situation, it idled for about 30 minutes before getting to redline, but the problem's not solved yet for me, I'm still trying to get it to idle longer without overheating. According to Duke and others, it's the lack of a vacuum advance on my car, which I am going to address in the next couple weeks.

I always did notice that on coolant refills, the system needed to purge air a couple times before it settled to the half full mark on the fill tank.

Regards,

Rich