L89 Question

[Rich G.]

Any L89 owners, past or present, here's the question. Does a properly maintained L89 suffer from cooling problems? Any difference as to model year? Is it a driveable configuration, or is the threat of over heating worse than an L71?

I'm interested in your observations.

Thanks

Rich Giannotti

[Joe L.]

Re: L89 Question

Rich-----

I've never owned or driven one. However, I can't imagine that the engine cooling for an L-89 would be significantly different than an L-71 of the same year. Except for the cylinder heads, all other components related to the cooling systems are identical. The L-89 aluminum cylinder heads and the L-71 cast iron heads should have approximately equal cooling properties, with the L-89 possibly a very little better due to the aluminum material and SLIGHTLY larger cooling passages. The L-71 and L-89 should be about equally "streetable".

[Duke W.]

Re: L89 Question

Aluminum has less thermal resistance than cast iron, so all other things being equal, it will transfer more heat. You definitely want at least a 180 degree thermostat and higher may be beneficial.

Assuming the radiator and fan are in proper functional order the biggest contributor to big block hot operation is the ported vacuum advance, which eliminates vacuum advance at idle. Converting L72/71/89s to full time vacuum advance will considerably reduce the tendency to overheat at idle and in low speed traffic situations.

The other change I recommend is to swap the '67 vacuum can for the specification used on the '66 L-72. This can has specs of 0 @ 6" and 16 @ 12". Since these SHP big blocks pull about 14" manifold vacuum at about 800-900 idle speed they will keep the vacuum advance "locked" at full advance at idle if full manifold vacuum is used as a siganl. Keeping the vacuum advance locked in at full advance is necessary for best idle stability and minimum heat rejection to the coolant.

The maximum vacuum advacne spec for '67 L-71/89 is 15 @ 15.5" according to the data I have from Corvette News, and idle vacuum is not enough to keep the diaphragm pulled to the limit at idle, however my Corvette P&A catalog shows the 1115360 as the replacement vacuum advance for all SHP big blocks from '65 - '70, and I believe this can has the specs that I quoted above for L-72.

The currect NAPA/Echlin VC1765 vacuum advance control is the same specification as the OE '66 L-72.

Duke

[Joe L.]

Re: L89 Question

Rich-----

One other thing: 1986 Corvettes with L98 were built with both cast iron heads and aluminum heads. The cooling systems were exactly the same for both. As far as I know, there was no significant difference in cooling or "running temperature" for L98s equipped with either type of cylinder head.

All 1987-91 L-98 Corvettes used aluminum cylinder heads with cooling systems pretty much the same as the pre-87 cast iron L98s. As far as I know, there was no difference in cooling or "running temperature" for these engines compared to the earlier cast iron head engines.

I think that any difference in the cooling caused by the aluminum head versus cast iron head are minimal and are easily accomodated by the inherent capacity of the cooling system. I think that the same thing would be true of 67-69 L-89s.

[Ralph E.]

Re: L89 Question

For what is is worth. I owned a 1968 L89 Convertible back then. It ran about the same temperature as my friends L68(400HP) and L71(435HP) cars. They were all hot. With the low ground clearance it would get pretty hot inside the car but it never overheated.

[Joe L.]

Re: L89 Question

Ralph-----

Yes, that's for sure; all big blocks pretty much suffered from marginal cooling capacity, especially at idle. With some carefully selected "tricks", I hope to avoid that when I finally get my "ZL-1" on the road.

What are the "tricks"? Well, a guy has to have some secrets. I MIGHT reveal them later, though. But, ONLY if the actually work.

[Rich G.]

Re: L89 Question

Thanks Joe and Duke et al. Your responses make sense (as usual).

Rich Giannotti

[Ralph E.]

Re: L89 Question

One thing that really will help a C3 temperature inside the car will be sidepipes. Stay away from headers. I speak from experience. Do NOT eliminate the T-stat to keep the car running cooler.

[Geoff C.]

She's Real Fine My L-89

[Steve Antonucci]

Re: L89 Question

Hey Joe,

I'll be looking for those big block overheat prevention tricks
in the future! Don't leave us hanging!!! BTW, thanks for the
info on the L/88.
Steve