I’m beginning the reassembly stage of my Vortec head swap and have run into my 1st. snag. The temperature sender from my old head won’t fit the new Vortec’s. I have reviewed the various posts on the subject and it appears I have two options. http://forums.corvetteforum.com/c3-t...ding-unit.html

One is to use my original sender unit and install it in the intake manifold.
Two is to use a sending unit for an 82 vette. It’s not clear in the post if the 82 unit will work with 78 gauges.

Does anyone know the part number of the 3/8 sending unit that will work with my 78 gauge? Worst case, I can always use option one but would like to find a sending unit that will work when installed in the head.

 

From my research I have not found a sender that will fit the smaller hole and still work with the '78 gauge. The '82 sender, which will fit the heads, will not match the '78 gauge.

You can drill and tap the hole in the head for the larger sender. You can install the stock sender in the intake manifold. You can have a '78 sender machined down and tapped for the smaller hole. You can find and install an '82 temp gauge to replace the '78 gauge.

That's about it, unless someone else knows of an interchange with another car or truck that will work.

 

Thanks Durango_Boy, I’ll probably install the sending unit in the intake manifold. While researching this on the forum, I stumbled across another potential cooling issue around coolant bypass and Vortec heads. http://forums.corvetteforum.com/c3-t...at-bypass.html
Do I need to run a coolant bypass on my stock L-82 block with Vortec heads installed?

 

No bypass that I am aware of and I don't recall anyone with Vortec heads on a Gen1 engine having any problems with keeping the engine cool. Usually if there is an overheating problem there are other issues that need to be solved and they have little to nothing to do with the head choice.

If you're worried about pressure under the T-stat just drill one or two small 1/8" holes in the brim of the T-stat to allow pressure and hot air pockets to seep through. Then when the coolant is hot enough the T-stat will open normally.

 

Maybe its just an issue with the later block designs. Here's a link that provides more info on a TPI setup. http://www.camaroperformers.com/tech...photos5-1.html

http://www.camaroperformers.com/tech...photos6-1.html
My heads are on now so I cant check the bypass passage.

 

I ran vortecs on my stockcar for several years, as well as the 406 which has yet to be installed in my vette. Never had any problems with overheating like you describe (and I beat on it hard). The intake manifold outlet is the best place for your temp sender, because this is the last spot the coolant can be measured before going to the rad for cooling. I gives the best temp indication of your engine.

 

I found pictures that I made of both my stock and Vortec heads.
http://picasaweb.google.com/Walllparty/CoolantBypass#

Notice the difference outlined in yellow. The Vortec heads appear not to have the water bypass hole drilled. To play it safe, I would think you would want to run a thermostat with a few 1/8 holes in it or a Stant SuperStat with the v-notch to allow a small initial flow before the engine reaches operation temp. It may not be a big problem but I would hate to overheat during my initial engine start and cam break in.

 

Don't worry about it.....The vortecs are a straight bolt on!!

 

I had the same issue with my Vortecs and mine is also a 78. I had my buddy in his machine shop turn the 1/2" npt to 3/8" put it in and works fine. If you dont have the access to a machinist, send it to me and I'll have it turned down for you.

 

I ended up using a 79 3/8" sending unit in the standard location on the head and it works OK?
Had a 190 stat and it read 190-200, then i put a 180 stat in and now it reads 180 to 190.
Well I think it dose, it is on my list to test the resistance at temp as compared to the 78 1/2" unit next spring and check the engine temp with heat gun.

 

I just pulled my 76 L48 and installed a Year one crate with vortec heads and found the same problem. I went to Checker auto and they suggested this sending unit. not sure if it will work yet but it fit the hole, 3/8, and supposed to be the same temp but i cant prove it.

 

I reread that old thread ... I have a OE pickup w/ OE vortec ... I understand the water hose from intake to pump issue ... I also know about the bypass hole in older blocks' passenger side wp flange. I know plenty of racers who plug this off w/ no problem ... lotsa hipo pumps don't have the hole either. Also, look at GMPP circletrack crate x602 ... it's an iron head vortec motor with an aluminum carb intake ... I've seen dozens of them and not one is running a bypass hose & no problems ... I've also read the manual that comes w/ x602 & it does not mention any bypass scheme hose or drilled t'stat. However, few run a t'stat, most have a simple restrictor in place of t'stat.

As for the OE wp hose ... it simply routes to the heater core while the other hose at heater core routes to Int manifold. I've seen plenty plugged at both wp & intake ... both older & vortec blocks ... no overheating problems. Like db said ... drill the t'stat if you think you may have an issue.

I cannot know, but suspect any "extra" holes in vortec deck are more likely related to improved coolant flow around cylinder-chamber rather than for bypass. Very much engineering done & continues toward equilizing temps from cylinder top-to-bottom so to reduce wall distortion so that tighter piston fit & less ring tension possible ... it does markedly help efficiency. Call em "green holes" ?? Some other mfg with open decks have introduced plastic inserts fitted in water jackets ... to assist control of passing coolant's dwell & path. I'm routinely astonished by their ingenuity ... almost as often as I curse em for mixing sae & metric threads.

 

Thanks for the feedback on the temperature sending unit guys. I’m about done with my cam and head swap so I’m going to stick with my stock sending unit and install it in the intake manifold to get me through the initial start and cam break in. That way I know what I’m working with and not changing too many things at once. There does seem to be a resistance difference between the 78 and 79 sending units from what I can find out on the web. The unit for a 78 WT203/TS6469 is 72 - 88 ohms @ 220F. The unit for a 79 WT359/TS6641 is 138 – 156 ohms @ 220F.

Jackson, thanks for the information on the coolant bypass differences between stock and Vortec heads. After all the research I did on Vortec heads, I never saw it mentioned either. It’s something other folks who are planning a Vortec swap should know about. I don’t expect to have any problems on my initial start after the swap but I will pay close attention to the cooling system temperature and operation. I did use the opportunity while I had the radiator out of the car to have it checked out at the radiator shop. The back flushed it and repaired 2 pin holes. Good as new!