Over heat issue 105 HP 1974 chrysler

Hello Guys

Need a little help, my 105 hp motor over heated a week or so ago, found out the pump was defective, housing pitted and replaced both the housing and the impeller, took it to the lake , tested it in the water still on the trailer and it worked just fine till i put it in gear and hit about 2800 rpm, pump stoped pumping again anf got hot , backed off the throttle and started pumping again, now im new to boat motors so are you not supose to run like that in the water on the trailer to test, the reason i did it that way is didnt want to get stranded out on the river, figured id trailer test it first. Any ideas. OH and i also replaced the check valve/relief valve for the pump on the side of the motor/ exaust manifold.

Re: Over heat issue 105 HP 1974 chrysler

High RPM , especially in gear, in a barrel will roil the water. You may have been sucking in exhaust gases through the pump, thus not delivering much water to the engine. Best to use Muffs or try it at the river.

Re: Over heat issue 105 HP 1974 chrysler

It was at the lake In 2 1/2 foot of water, I'll try the river before I do anything else .

Re: Over heat issue 105 HP 1974 chrysler

I think that engine has a bypass relifevalve. If you have problem with that you can loose water at high speed.

Re: Over heat issue 105 HP 1974 chrysler

I allready replaced the check valve/ relief valve, it was weak, retested it at the lake sitting on the trailer and did the same thing.

Re: Over heat issue 105 HP 1974 chrysler

When you had the water pump off, did you reach down, pull up the plastic screen and clean it?

I know it is almost impossible to do wrong, but did you place the stainless plate on correctly? Are you certain that the drive key is still in position? It is possible to pop them out of the slot when installing the impeller.

Did you use the gasket below the stainless plate? Did the new pump come with a top seal? If not, did you install one?

There are two different length bypass valve covers and two different matched springs. Did you get the correct spring with the cover you have?

BTW: Force eliminated that bypass so you could plug the 3/8 hole woth a short length of rod epoxied in. Don't go in too far though or you will restrict the water passage. Use the plastic valve plug as a guide.

Water intake on that engine is rather high, above the gearcase, and testing on a trailer may just cause loss of pick-up. Test it on the water and don't go too far from the dock. If she still heats up at 2800, then go back slowly.

Re: Over heat issue 105 HP 1974 chrysler

Didnt see a screen, looked all up and down the lower unit and ran a coat hanger down to the opening to make sure it was clear, the water comes out at idle like gang busters out the two holes . but i will put the plug in the relief valve, this is a great running motor and want to keep it running as long as i can, baybe rebuild this winter. the compresson is 120 115 115 105. but it is getting hard to find parts, it looks very easy to rebuild,

Re: Over heat issue 105 HP 1974 chrysler

Took it out to the river last night, ran fine for about an hour, then bam it over heated again, was running about 10 minutes at WOT , engine died, but did restart, let it cool down at idle, then made my way back to the trailer, looks like the check valve / relief valve even though i did replace it, maybe the wrong one ? I see in Franks post that I can plug the passage , this looks to be a very simple thing to do, ill give it a try and let you know, thanks frank !!!!!!!!!!