[Blocked Exhaust Crossover] [RADIATOR HOSES] [MANIFOLD GASKET]


UPPER   (455) 689922 7726 689922 60964 20598
               (403) 2015466

LOWER (455) 689921 8796 689921 85114
               (403) 2015465

I went to the NAPA wherehouse in San Diego.  The guy let me thumb through a book of radiator hoses.  The NAPA number for the lower is 8796.  I bought two of them so I can carry a spare.  It came with the inner spring.  They cost me $16.71 each after my AAA discount.  You need to cut
about 4 to 5 inches off one end.  Just hold it up next to your old hose and, you will see how much to cut.  Once you get it on, it fits like a glove.

  the NAPA number for the upper is 7726.Bob Sobrito,

BTW There was mention of the radiator hoses some time ago. Cinnabar 455
numbers are- Lower rad hose #689921 ($26.00) and Upper #689922 ($24.00)Richard

Larger Radiator Core

I had my radiator re cored here in San Diego a few years  back.  In talking with the radiator repair shop about a heating problem I was having, he asked if I wanted a larger radiator core.  There is a core available that will fit the tanks on our GMCs which has 53 rows of tubes compared the stock 42 rows.  It has the same 14 fins per inch and the same tube size as the OEM core; the tubes are a little closer together.
This core will provide around 20% more cooling capacity then the OEM core.  With this larger core, I can not force by engine temperature above 195 degrees F (when the fan clutch kicks in), even when towing my Tracker up a 7 % grade under full throttle with an outside temperature of 110 degrees F and with the A/C running.  Try one-you will like it.Chuck Aulgur
First radiator guy said 14 fins per inch would restrict the flow to the rear tube, I said that was the GMC stock and that was what I wanted, he argued a bit and then  he looked it up found that was the stock configuration.

Then he said the 53 tubes would restrict the air flow and should go with 10 fins per inch, I said nope, I know I want  14 fins per inch and just wonder what the cost difference would be...... the cost was more than I thought and others might get a better deal but this is what he came up with

10 fins per inch 42 tubes (what I had)  $360
14 fins per inch 42 tubes (stock)          $380
14 fins per inch 53 tubes                       $440

I had mine done at Cat's Radiator here in California. Gene
Do not depend upon any number, ask for what you want, the numbers do not seem to get it all done

    Some of the old line radiator manufacturers, like Modine, have gotten out of the business of supplying custom-spec cores for rebuilding.
One company, GO/DAN Industries, which has now been bought by Transpro still does this.  (As of Dec 02 they are still in the process of name change.)  They say they can make just about any combination of rows, fins per inch and tubes on a custom order in 3 or 4 days.  

They offer two different core designs:  the VT and the MX cores.  Their stock VT core corresponds to the stock GMC motorhome when ordered as a 4 row, 14 fins per inch, 42 tubes in the GMC size of 24 inches tall by 28.25 wide.  The radiator shop will put this new core into your existing side tanks.

The MX core is GO/DANS "killer ap" .....the best they make re: cooling capacity, and it meets all the specs and dimensions of the VT core except that it has 59 vs 42 tubes.  I spoke to the manufacturing plant in San Bernadino and the bottom line is "this can't be beat" as it is the ultimate in cooling capacity..

Further, the factory says either the VT or MX cores can be had with "dimpled" tubes which give additional area for more cooling.  At a cost increase of 15% for a 3 % gain in cooling.  After talking with the factory, I came away with the impression that the MX core with "dimpled" tubes could not be beat IF one could afford it.  HOWEVER , the local radiator shop told me that the dimpled tubes can not be "rodded out" (cleaned) in the future.  (I did not ask the factory if this was true)..  Based on that input, I decided against the "dimpled" tube, and the 15%cost increase and went with the MX core, which is about 35% more expensive than the stock-equivalent VT core.  This custom MX core was available to the radiator shop overnight from San Bernadino to Fresno at no freight cost .  (I didn't ask how or why, perphaps they have the GMC size in stock?  Maybe there was one already in Fresno?)  Or they can make it VERY quickly.

I inquired about the GO/DAN part number 128751 listed on your site as "a 16 fin" and was told by GO/DAN that:   (a) it is a 12 fin, and therefore has less cooling capacity  than a 14 fin and (b) can not be had in "dimpled" tubes.  Consequently I ordered the MX core with the OEM spec of 14 fins/inch, 4 row,  and of course it has 59 tubes over the OEM of 42 for more water tube-to-air contact.

IMPORTANT:  One point to be aware of:  I was told by GO/DAN that most, if not all, GM OEM radiators in the past, (including the 1970's that we are concerned with) were constructed with what is known as "GM side plates" (which in the case of the motor home are on the top and bottom, due to side tanks).  These are more or less "C" shaped brass pieces that run the full width of the core.  These are strengthening plates to prevent "balooning" of the core under heat and pressure..  GO/DAN no longer has any GM side plates.  None of their factories across the US has any in inventory (I had them check), and their supplier no longer makes them.  So, it is important to bring this up with your shop doing the work.  As of this writing, (Dec 02) GO/DAN does supply what they term a generic "C" channel  which is included in the cost of the core IF specified.   This is not the same as the OEM "GM side plate", but used in place of it.  I was advised by the radiator shop not to try and reuse the original...mainly due to the cost of the labor to R&R the original,  as I understood it.).  In my case, the local shop offered two solutions to prevent "balooning" of the core...which over time will weaken it and cause leaks.  BOTH choices include using the GO/DAN-supplied "C" channel.  The two choices were (1) to band it with metal strapping (as used on crates) or (2) to braze strengthening rods, top to bottom, between the two new "C" channels.  This shop uses the metal banding all the time on big industrial radiators and said either would work just as well.   I choose to go with the rods.  (For no other reason than the rods have less surface area than the steel banding to block airflow, which probably isn't critical with either VT or MX core, especially the MX core.)  There are two vertical rods, evenly spaced, i.e. dividing the core into thirds, that are about 1/4 inch in diameter.  These are brazed to the new "C" channels on the top and bottom on both the front and back of the radiator core.  Positively locating the top and bottom "C" channels to prevent "balooning".

A final comment:  there is a listing of NAPA part numbers for top and bottom radiator hoses.  It is mentioned that the bottom hose (p/n 8796) has as a spring in it.  I purchased one from NAPA on Dec 11, 02 and it does NOT have a spring in it.  Either NAPA has dropped the spring, or we need to find a substitute hose with a spring.

GO/DAN REFERENCE:  (1)  On the web.  go to www.transpro.com  (2) click on 'skip intro', (rather faint 2/3rds down)  (3) on the home page, click on LOCATIONS (the black bar near the top of the page) (4) choose and click on MANUFACTURING LOCATIONS and find the location in the state  nearest to you.  I suggest you call them for any technical information as that is who your local radiator shop should call.  Its best you know more than the shop doing the work to begin with. 

The LOCATIONS link will also give you a map of the local distributors across the U.S.   As of Dec 02 there is no link to their local addresses, only stars on a map, but there are email links to the Eastern and Western sales managers that might locate a local distributor for you.  If you call your nearest manufacturing location (San Bernadino for Calif) they will give you the local distributor nearest to you.  For me, it turned out that there was one in my own city of Fresno.  They DO NOT sell to anyone but radiator shops, however.  They will probably give you a list of shops they do a lot of business with if you don't know where to turn for quality work.

I hope this saves someone a lot of time.  It won't be cheap but it will be right.

 My recommendation:  Find more than one radiator shop whose work you trust and get a firm price quote on the core you choose.  The cores are priced by GO/DAN to the radiator shops by the square inch (678 sq in for the GMC) for each different core model.  Depending on the shop, they may have different cost structures based on their purchasing voluume which determines their unit-cost.  In my case I went to  a shop I have used many times as a long-time customer and know their work, AND because I had a seasonal-promotional 20% discount cupon (recently arrived in the mail), on parts and labor, that was to expire in one week!   I did not take my advise to "shop it around" as I figured I could not do any better.   (The shop was not expecting the 20% discount but had to honor it to their chagrin.)I  hope someone comes up with an equally effective solution for less money!!!   Stephen Dean.

Took my radiator to Cannfield Radiator in Utica NY this morning. I was told they use cores from Go dan Industries (GDI)(http://www.godan.com/  ) which is a standard used all over the country. When I told him I wanted a 14 fin/inch, 4 row, 53 tube radiator core or better he selected a GDI 12-8751 which has 16 fins per inch. with the same other specs.  It is used in the large GMC top kick trucks 

Total cost is $295 which includes the new core, complete boiling and bead blasting of the end caps and painting of the completed radiator.

I cant imagine overheating with this new radiator. Not the time to do it, but luckily it developed a leak here and not 1/2 to florida. He told me that  the bottom started to rot out and I was lucky to see the small drips when I inspected it.

If you do replace your radiator be sure and also replace the old  radiator supporting pads (shown on page 6-2 of the parts book as item 2, part number 3901449). The supports can be ordered from your CMC truck dealer under new part number 15502586 and they cost $3.30 each and come in a bag of 5. You need 4.Tom
on a 1977 Palm Beach with the 455 engine, the rubber supporting pads had to be cut to allow the radiator to fit between them (insufficient space between the upper and lower support pads). Approximately 1/4" of thickness had to be removed from the "back" of the pads and the corners cut at 45 degrees to clear the radius in the brackets.  If the pads are installed as a direct replacement for the original ones there is insufficient room for the radiator. I could not get the top part of the core support to bolt up to the lower U-bracket until the pads were altered. Others
may have this same problem. The prices are also out of date as you might imagine, you might want to say "about $4 each".Bob Burkitt  

Radiator Removal (6/13/06)

Go look at these pictures to see how to remove the radiator and the difference in the cores.  There is also some text there.

Out-the-bottom pictures-- the easy way out

To remove the radiator you do not have to remove the cage.  Disconnect everything going to the radiator & items in front of radiator. (you also have to loosen but not remove the top plate of the frame over the radiator) You don't have to remove the connections to the AC just pull the condenser forward.  Lift radiator up & then out at the bottom (toward bumper) & down & out it comes.  Simple item to remove ..... shroud etc. stays in place. Duane

On my '73 I renewed all body mounting rubbers and now have adequate room to loosen the top bracket and lift the radiator enough to slip it out at the bottom. Takes me no more than 20 minutes to take out the radiator, no matter where I am. Marc Hogenboom

 If your mounting rubbers are in bad shape, you might have to modify the frame so that you can remove the radiator.  Here is a great example.

 This is how I modified the radiator frame to makei t easy to remove and install the radiator.   Took less than 45 minutes to install. J.R. Wright


Blocked Exhaust Crossover

The exhaust crossovers in the 455 heads and intake manifold are entirely too big for their design purpose:  quick carburetor warm-up in cold weather and prevention of carburetor icing, primarily the former. Consequently, the carburetor gets entirely too hot, causing vapor lock and boiling out the gas in the float bowl after engine shutdown.  In fact, there is so much heat
conveyed to the top of the engine that it's the second most significant contributor (perhaps even the first) to hot engine compartments.  A look at the intake manifold in the lateral area of the carburetor, where the crossover passes from one head, under the carb, to the other head will show the paint literally burned off -- that probably takes 300F+.  Any wires, rubber hoses, etc., in that area are probably baked hard, even if not touching the manifold.

Inside the engine, the standard intake manifold gasket is a "turkey tray" -- a sheet metal shield which extends all the way across the underside of the intake manifold.  That's there to provide some protection for the camshaft area, and the engine oil circulating in that area, from the intense heat on the underside of the intake manifold.  That underside is guaranteed to be black with carbonized engine oil.
This  carbonized engine oil is a big problem.  Here is a picture by Kelvin that shows the debris falls into the engine and plugs the oil pump

A frequent problem with 455s is cracking of the intake manifold, with resultant fuel mixture disturbance and performance problems.  The cracks are caused by overheating from the exhaust crossover. Blocking the exhaust crossover eliminates all those problems.  It has some possible ill effects, the foremost, and far most likely, is slower warmup during cold weather.  I personally have heard no complaints about that. Plugging the crossover also renders the carburetor choke inoperative because
it obtains its heat from air circulating through a tube inserted in the intake's crossover.  That is easily corrected with an inexpensive electric heating element for the choke.

There are a number of ways to plug the exhaust crossover.  Undoubtedly the best way if the heads are removed, is to have plugs welded into the ports in the heads.  That should only be done by an  engine machine shop which is highly experience at welding and machining engine cylinder heads.  Richard Archer did that to his, as did several others I know.  Pictures are
available somewhere that I don't recall now.

Another method is to insert loose plugs in those head ports.  I strongly recommend against that method.  The pictures referenced below will show why: 




I will only tell you what I have done and my perceptions of what I have accomplished. I blocked off my crossovers.

There seems to be two options on how you can do this. First there are the SS plates sold by Mondello, and Patterson.

The second  option. Mondello sells a aluminum alloy you can pour into the cross
overs. Saw somewhere that burned out too.

Here are Pictures of  how Mondello does it:

Here are pictures on how it is done at home by Ken

I did have an email discussion with one person that said that his plugs had eroded around the edges  after 5 years--they were not welded in. (Motorhome Marketplace magazine, P-6, 1993)  I decided to take my own path. I have a shop here that does nothing but weld up heads for the mines around here. He does it everyday. My engine had been rebuilt and two valve seats were leaking into the water jacket---very little but it was there. The shop said that welding up the valve seats would be no problem. Well, my thought was if you are going to weld on a head you may as well go all the way. We shortened down the plugs and welded them in place.

This  can be seen in photos at:

Do I recommend this----no. I have no idea if this is going to work or not. Do I trust the guy who did it--yes. He heats up the heads then welds on them----then he heats them hotter and brings them down to room temperature overnight. The next day we CCed the heads down to a  uniform 69 ccs. Right now I am very happy. I have only run the engine for 3500 miles so I have no idea what the long term holds.

Here is what I think I know: The bright blue manifold you saw in the pictures is still the same color. No discoloration what so ever. When I got my lady there were melted wires and conduit on top of the engine. For this trip I laid a piece of wire, conduit and vacuum hose on top of the manifold. All survived the trip with no damage. I can touch a manifold runner and it  is very warm but not hot. The heat coming off the top of the engine has been reduced by a large margin. I installed an electric choke. I also made sure that all of the systems that draw air from around the exhaust manifold while the engine is cold were working. While I was in Houghton, MI. there
were several mornings that it was only in the upper 30s. I started the engine each morning. It would take about 1 min of playing with the throttle to keep her running then she would settle down and run fine on her own with no  help from me.

Another thought about all of this. When we tore down the engine I was not happy about what I found under the valley pan. There was a whole lot of burned oil caked on it. By blocking off the crossovers I was able  to do away with the valley pan. It was also the source of one intake
manifold leak. Mondello sells a sheet metal gizmo that shields the push rods so you dont need the valley pan. With the crossovers blocked oil should not get burned up there. While we were at it we milled the  exhaust ports on the heads and the exhaust manifolds----well yeah we did a little more. Put it all back together with no gaskets---still no leaks. Going to say one last thing that may get me thrown out of here. There is no way I would put grade 8 bolts in an exhaust manifold.

Jim I dont do this very often but there is one thing I have to say that you have to do. Take your intake manifold down and have it magnafluxed. The people I trust around me say that most of the intake manifolds of that era with crossover are cracked. Mine looked good after hot tanking and bead blasting but it had so many cracks it was unbelievable. One shop I worked with on this project even told me that in that era when somebody brought in warped or cracked exhaust manifolds that he would not even work on them unless they brought in their intake manifold to be checked. Hope this is not a lot more than you wanted to know.  Take Care Arch

When I purchased my '77 Classo last year - it had a burned #4 exhaust valve. The manifold had a crack right under the carb. when you have a burned exhaust valve in one of the middle cylinders - it seems that is almost always because exhaust gases are mixing with the charge and leaning out the mixture - it also seems to effect the middle cylinders first. I replaced the manifold with a part from a junk yard. The 403 manifold is the same in the motorhome as the passenger cars (I also believe that any 350 manifold also fits) - this is not true for the 455 manifold  (which is special for the motorhome). Just my experience Pete


I must sadly report that the Edelbrock iron exhaust port plugs are NOT a good way to block the intake manifold exhaust crossover.  When I got the manifold off this morning I found that the plugs had been eroded by the exhaust gases and that they had damaged the cylinder heads.  That despite
the facts that I had them fitted tightly 25,000 miles ago and that the crossover passage in the manifold itself was completely sealed with Mondello Metal.
I've posted pictures at:

The plugs themselves were considerably smaller than when I installed them. They originally had as-cast surfaces except where I'd ground them to fit snugly into the ports.  Now they're smooth all over except where they've had chips broken out of them.  Rather than being cast iron gray or black, they're brick red (the pictures don't show that well because my greasy hands had been all over them), as are the stems of my exhaust valves.

The ports are eroded, especially at the bottom where they look as if they've been attacked with a ball peen hammer.  At the backs of the exhaust ports the plugs have worn through the iron of the head and into the head bolts located there.  See photos 2-4 (my 10, 11, & 12).

At first I was a bit panicked by the damage I saw but after looking at it for a while, I think the engines' OK to use.  Those two head bolts may be a problem to remove by the time they've been exposed to exhaust gases for another 100,000 miles -- but I'll worry about that then! :-)

Since I'm getting 800+ miles per quart of oil I'm surprised how much oily deposit I have in the intake ports and on the intake valve stems.  How does that look to you engine experts?

The first picture shows a plastic object I found lying on the turkey pan. Can anyone identify it?

The Mondello Metal in the intake manifold stood up well.  Other than being darkened, it looks just like it did when I installed the manifold.  The fact that the Mr. Gasket 404 didn't have exhaust ports cut into it is now corrected -- the material has been completely burned away there -- I've no idea whether they expected otherwise.

At one place in Mondello's Technical Manual (which book I can't locate at the moment) he suggests using a turkey pan with the gasket flanges cut off as a windage tray when using a fiber gasket.  That was specifically for a 403, for which he didn't offer a windage tray, but I took it as a valid option for the 455.  It was not a good idea.  As can be seen in the last photo in the album, some of the "ears" left on to hold the tray in place broke off.  Two of them were laying in the tray.  I've got to hunt the others -- hopefully they're laying in the bottom of the oil pan.  Another BAD IDEA!

One idea that did work good is the silicone sealant at the ends of the intake manifold.  As suggested here by someone, I dimpled the gasket bearing surface thoroughly with a center punch.  A large-enough bead of silicone was allowed to skin over and then the manifold was set into place carefully.  If I couldn't have gotten a putty knife into the ends to cut that silicone, I don't know how I'd have removed the manifold because it was securely locked in place!

 Consider using a "Mr. Gasket" #404 intake gasket. It is a composition gasket without the "turkey pan" and will seal an imperfect fit. This gasket comes with no holes cut for the exhaust to come into the intake manifold. Ideal if you have this blocked but easy to cut if not.DENNY